This document discusses the history of determining the age of the Earth. It describes how early estimates ranged from thousands of years based on biblical interpretations to hundreds of millions of years based on experiments measuring cooling of materials and sediment accumulation. The development of radiometric dating in the early 1900s allowed for more precise measurements by analyzing the decay of radioactive isotopes. Radiometric dating of the oldest rocks and minerals has provided evidence that the Earth is approximately 4.5 billion years old and the solar system formed around 4.6 billion years ago.
The document discusses the history of determining the age of the Earth. Early estimates ranged from thousands to billions of years based on different methods and assumptions. In the late 19th century, radioactive dating methods were developed that provided evidence the Earth was millions to billions of years old, conflicting with a literal reading of the Bible. This sparked debates around assumptions made in dating methods and their application to estimating the Earth's age. While techniques have improved, disagreement remains on interpreting results within biblical or long-age frameworks.
1) The oldest rocks on Earth are around 3.7-3.8 billion years old based on radiometric dating.
2) Even older zircon crystals around 4.0-4.2 billion years have been found embedded in younger rocks.
3) The best estimate for the age of the Earth itself comes from lead isotope dating of meteorites, yielding an age of 4.54 billion years.
1) The document discusses the origin of the universe according to the Big Bang theory. It describes how the universe began as a very small, dense point and has been expanding ever since.
2) The Big Bang theory gained support in 1964 with the discovery of cosmic microwave background radiation by Penzias and Wilson. This provided evidence that the universe had a hot, dense beginning.
3) The theory proposes that nearly 14 billion years ago, the entire visible universe was condensed into a very high density and high temperature condition, and then began rapidly expanding.
Astrochemists study the chemistry of other planets and stars by working with astronomers and geologists. They analyze the chemistry of atmospheres, elemental makeup of stars and asteroids. This involves studying the chemistry and any organic compounds that may be present on other celestial bodies both near and far from Earth, including detecting organic molecules in very young galaxies over 10 billion light years away using infrared spectroscopy. A key finding is that over 90% of the mass of the human body consists of stardust from elements created in supernovas and scattered across the universe.
Surface exposure dating is a collection of techniques used to estimate how long geological materials have been exposed at Earth's surface. It dates events like glacial advances, erosion history, lava flows, and meteorite impacts. There are two main methods: absolute dating provides accurate ages, while relative dating determines the sequence of events without specific dates. Examples of absolute techniques include radiocarbon dating, potassium-argon dating, and luminescence dating. Relative techniques include stratigraphy, seriation, and fluorine absorption dating. Surface exposure dating has applications for reconstructing glacial chronologies, shoreline changes, landscape development rates, and volcanic and archaeological timelines.
In 1953, Francis Crick and James Watson discovered the double-helix structure of DNA, publishing their findings in Nature. In 1955, Louis Essen invented the first accurate atomic clock based on the caesium-133 atom. In 1957, the Soviet Union launched Sputnik 1, the first artificial satellite, demonstrating their capability to launch objects into space.
The document provides an overview of cosmological theories and astronomers throughout history. It discusses Ptolemy's geocentric model, Aristarchus and Copernicus proposing heliocentric models, Tycho Brahe's observations, Galileo discovering Jupiter's moons and sunspots, Kepler's laws of planetary motion, Newton's law of universal gravitation, Gamow's Big Bang theory, Hubble confirming other galaxies, the steady state theory, and old earth creation theory accepting the age of the Earth but questioning evolution.
This document provides an introduction and overview of an astrochemistry course. It defines key terms related to astrochemistry including astronomy, chemistry, physics, biology and their intersections. It describes how astrochemistry emerged from the early universe following the formation of the first atoms, and how stars then formed and spread heavier elements through nebulae and supernovae. The course will examine astrochemistry from the early universe to present day, exploring topics in astrophysics, astrochemistry and astrobiology within our solar system and beyond. It will include both traditional coursework and hands-on demonstrations to provide an interactive learning experience.
The document discusses the history of determining the age of the Earth. Early estimates ranged from thousands to billions of years based on different methods and assumptions. In the late 19th century, radioactive dating methods were developed that provided evidence the Earth was millions to billions of years old, conflicting with a literal reading of the Bible. This sparked debates around assumptions made in dating methods and their application to estimating the Earth's age. While techniques have improved, disagreement remains on interpreting results within biblical or long-age frameworks.
1) The oldest rocks on Earth are around 3.7-3.8 billion years old based on radiometric dating.
2) Even older zircon crystals around 4.0-4.2 billion years have been found embedded in younger rocks.
3) The best estimate for the age of the Earth itself comes from lead isotope dating of meteorites, yielding an age of 4.54 billion years.
1) The document discusses the origin of the universe according to the Big Bang theory. It describes how the universe began as a very small, dense point and has been expanding ever since.
2) The Big Bang theory gained support in 1964 with the discovery of cosmic microwave background radiation by Penzias and Wilson. This provided evidence that the universe had a hot, dense beginning.
3) The theory proposes that nearly 14 billion years ago, the entire visible universe was condensed into a very high density and high temperature condition, and then began rapidly expanding.
Astrochemists study the chemistry of other planets and stars by working with astronomers and geologists. They analyze the chemistry of atmospheres, elemental makeup of stars and asteroids. This involves studying the chemistry and any organic compounds that may be present on other celestial bodies both near and far from Earth, including detecting organic molecules in very young galaxies over 10 billion light years away using infrared spectroscopy. A key finding is that over 90% of the mass of the human body consists of stardust from elements created in supernovas and scattered across the universe.
Surface exposure dating is a collection of techniques used to estimate how long geological materials have been exposed at Earth's surface. It dates events like glacial advances, erosion history, lava flows, and meteorite impacts. There are two main methods: absolute dating provides accurate ages, while relative dating determines the sequence of events without specific dates. Examples of absolute techniques include radiocarbon dating, potassium-argon dating, and luminescence dating. Relative techniques include stratigraphy, seriation, and fluorine absorption dating. Surface exposure dating has applications for reconstructing glacial chronologies, shoreline changes, landscape development rates, and volcanic and archaeological timelines.
In 1953, Francis Crick and James Watson discovered the double-helix structure of DNA, publishing their findings in Nature. In 1955, Louis Essen invented the first accurate atomic clock based on the caesium-133 atom. In 1957, the Soviet Union launched Sputnik 1, the first artificial satellite, demonstrating their capability to launch objects into space.
The document provides an overview of cosmological theories and astronomers throughout history. It discusses Ptolemy's geocentric model, Aristarchus and Copernicus proposing heliocentric models, Tycho Brahe's observations, Galileo discovering Jupiter's moons and sunspots, Kepler's laws of planetary motion, Newton's law of universal gravitation, Gamow's Big Bang theory, Hubble confirming other galaxies, the steady state theory, and old earth creation theory accepting the age of the Earth but questioning evolution.
This document provides an introduction and overview of an astrochemistry course. It defines key terms related to astrochemistry including astronomy, chemistry, physics, biology and their intersections. It describes how astrochemistry emerged from the early universe following the formation of the first atoms, and how stars then formed and spread heavier elements through nebulae and supernovae. The course will examine astrochemistry from the early universe to present day, exploring topics in astrophysics, astrochemistry and astrobiology within our solar system and beyond. It will include both traditional coursework and hands-on demonstrations to provide an interactive learning experience.
Earth is the third planet from the Sun and the largest of the terrestrial planets. Unlike the other planets, Earth's name comes from the Anglo-Saxon word "erda" meaning ground or soil. The Earth formed approximately 4.54 billion years ago and is the only known planet capable of supporting life. Additional facts: the Earth has one natural satellite (the Moon); it has a powerful magnetic field generated by its nickel-iron core that protects the planet; and it has the greatest density of all planets in the solar system.
Astronomy is one of the oldest sciences, with early civilizations like those in ancient China and at Stonehenge making careful records of astronomical phenomena. The field advanced significantly with Greek philosophers and scientists developing early mathematical models. Claudius Ptolemy created an influential geocentric model of the Solar System in his work The Almagest. Later, Nicolaus Copernicus developed the first heliocentric model placing the Sun at the center. Johannes Kepler then established his three laws of planetary motion, and Isaac Newton later formulated his law of universal gravitation and invented calculus, greatly advancing our understanding of astronomy.
This document provides information about the planet Saturn. It discusses Saturn's distance from the sun, diameter, temperature, rotation period, number of moons, composition and other key facts. It specifically mentions that Saturn is known for its prominent ring system, which was discovered by Christian Huygens in 1665 and that the Cassini Division, a gap within the rings, is named after Giovani Cassini who discovered it. The rings extend from 6,630 km to 120,700 km from Saturn's equator and are composed primarily of ice particles.
1) Early civilizations made observations of celestial objects to predict seasons and aid in navigation. The geocentric model proposed by Aristotle placed Earth at the center of the universe.
2) Planets were observed to move irregularly compared to other celestial bodies. Ptolemy proposed epicycles to explain retrograde motion within his geocentric model.
3) Copernicus suggested a heliocentric model where Earth and planets orbit the sun. Galileo's observations with a telescope supported this model.
4) Kepler developed his laws of planetary motion describing elliptical orbits with the sun at one focus. Newton later described universal gravitation explaining the forces at work.
This document discusses galaxies and our cosmic future. It begins by describing our own Milky Way galaxy and showing images of other galaxies, including spiral and elliptical galaxies. It then discusses galaxy luminosity functions and observations made using large telescopes. The document concludes by noting it was presented by Charles Liu at the American Museum of Natural History on September 23, 2011 and was about galaxies and our cosmic future.
- Dinosaurs lived on Earth for over 165 million years from the late Triassic period until the end of the Cretaceous period 65 million years ago. They varied greatly in size and appearance.
- Extinction occurs when a species can no longer adapt to environmental changes, leading to their death. A popular theory is that an asteroid impact caused the mass extinction that killed the dinosaurs. However, some evidence challenges this and suggests massive volcanic eruptions may have been responsible.
- The document discusses and provides evidence for both the asteroid impact theory and volcanic eruption theory for the cause of the dinosaur extinction. While the asteroid theory was widely accepted, newer evidence is increasingly supporting the volcanic eruption theory as well.
1. Astronomers detected a planet orbiting Proxima Centauri, the star closest to our sun, that is 1.3 times the mass of Earth and sits within the star's habitable zone.
2. Scientists from LIGO detected gravitational waves from the collision of two black holes over a billion years ago, confirming Einstein's theory of relativity.
3. Archaeological discoveries in Australia have shown that humans have inhabited the continent's interior for at least 49,000 years, 10,000 years longer than previously thought.
The document traces the development of scientific understanding of the solar system from ancient times to the modern era. It describes early geocentric models proposed by Anaximander and Ptolemy that placed Earth at the center. Later thinkers such as Aristarchus, Copernicus, and Galileo proposed heliocentric models with the Sun at the center. Kepler determined orbits were elliptical rather than circular, and Newton explained planetary motion through universal gravity. Edwin Hubble's discovery of an expanding universe led to the development of the Big Bang theory.
This document discusses biosignatures and the search for habitable exoplanets. It begins by reviewing Earth's biosignatures like oxygen, ozone, methane, and vegetation reflectance. It then explains that life exploits chemical energy gradients and metabolic reactions have an energy yield that can be quantified. The search for habitable worlds involves finding transiting exoplanets using ground and space telescopes to measure atmospheres. Direct imaging from space is also needed to find and characterize Earth analogs, with external occulters showing promise to block starlight. The overarching goals are to understand possible biosignatures on non-Earth worlds and find the most promising planets for atmospheric study.
The document discusses the history of Earth and how its environment has changed over billions of years. It describes how astronauts saw Earth as a single moment in time, and how the continents have shifted locations over hundreds of millions of years. It also explains how climate changes, like ice ages, have significantly altered Earth's surface and influenced human migration patterns in the past.
Spiral galaxies consist of a flat, rotating disc containing stars, gas and dust, with a central bulge. Elliptical galaxies are the most common type of galaxy and contain less gas and dust. Irregular galaxies have an irregular, chaotic appearance without distinct structure. Edwin Hubble proved in 1925 that the universe is expanding based on the relationship between galaxy distance and velocity.
- The Galileo probe explored Jupiter and its moons from 1995-2003, discovering evidence of subsurface oceans on Europa and volcanic activity on Io. It was the first spacecraft to fly by an asteroid and discover a moon orbiting an asteroid.
- Col. Eileen Collins was the first female shuttle commander, commanding missions STS-93 in 1999 and STS-114 in 2005. She has logged over 872 hours in space.
- The Mars Pathfinder mission in 1997 proved that a rover could be placed on Mars cheaply, sending back over 17,000 photos and 15 chemical analyses before ending in 1997.
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of pre-history: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy, and not completely disentangled from it until a few centuries ago in the Western World (see astrology and astronomy). In some cultures, astronomical data was used for astrological prognostication.
Ancient astronomers were able to differentiate between stars and planets, as stars remain relatively fixed over the centuries while planets will move an appreciable amount during a comparatively short time.
SideriusNuncius, also known as The Starry Messenger, was a 56-page scientific treatise published in 1610 by Galileo Galilei describing his astronomical observations using the newly invented telescope. In it, he described observing the surfaces of the moon, the Milky Way resolved into individual stars, and four of Jupiter's moons, which provided evidence against the Ptolemaic geocentric model of the universe. The work was important as the first scientific treatise addressing the telescope and its observations, demonstrating the scientific method and establishing observational astronomy as a field.
Galileo Galilei was one of the first people to make quality telescopes, which he used to make important astronomical discoveries such as the moons of Jupiter. He observed that Venus has phases and that Copernicus' heliocentric model of the solar system was more accurate than the geocentric model endorsed by the Catholic Church. Galileo openly challenged the Church's teachings, which led to conflict between science and religion. His discoveries and willingness to question established beliefs were pioneering and helped advance astronomy.
This document discusses the fine-tuned universe theory, which argues that the universe appears carefully designed to support life. It outlines several factors that must be precisely tuned for life, such as the organization of matter into atoms and precise mass relationships between subatomic particles. The document also reviews ideas about the origin of the universe, such as the Big Bang theory and biblical creation account. It provides illustrations of astronomical objects and facts about the immense scale of the universe.
1. The document discusses the history of astronomy from ancient Greek ideas of a geocentric universe to Copernicus' heliocentric model.
2. Key figures discussed include Ptolemy, who developed the geocentric model that dominated for over 1000 years, and Copernicus, who proposed placing the Sun at the center.
3. Kepler later determined that planets orbit in ellipses rather than circles, establishing his three laws of planetary motion.
This document provides a history of astronomy from ancient Greece to modern times. It describes how early Greek astronomers like Aristotle and Hipparchus made early observations of celestial objects but believed in a geocentric model where Earth is the center. Ptolemy later created an elaborate geocentric model, though Copernicus, Kepler, and Galileo provided evidence supporting a heliocentric model through observations, Kepler's laws of planetary motion, and Galileo's discoveries with the telescope. Newton later unified physics and astronomy by formulating the law of universal gravitation. Einstein then revolutionized our understanding of motion, space, and time through his theory of relativity.
This summary provides the high-level information from the lengthy document:
- The document discusses various topics related to nuclear energy and radioactive materials, including nuclear reactors, radioactive waste, and nuclear accidents.
- Specific events mentioned include the Chernobyl disaster, the Columbia space shuttle accident, and nuclear weapons accidents involving B-52 bombers.
- The document also references different types of nuclear facilities and technologies, such as nuclear power plants, research reactors, nuclear weapons, and medical uses of radioisotopes.
The document provides a timeline of important figures and events in astronomy from 3000 BC to 1727 AD. It summarizes the key contributions of figures like Aristarchus, who proposed the heliocentric model of the solar system; Ptolemy, who proposed the geocentric model; Tycho Brahe, who built important observatories; Galileo, who used telescopes to study astronomy; Kepler, who discovered the laws of planetary motion; and Isaac Newton, who discovered the law of universal gravitation and helped prove the heliocentric model. The timeline also notes the invention of the telescope in 1608, which greatly advanced the study of astronomy.
Este documento es una guía de compras publicada por el periódico El Universal en marzo de 2015. La guía contiene múltiples artículos sobre diferentes productos y servicios disponibles en ese mes para los lectores.
Earth is the third planet from the Sun and the largest of the terrestrial planets. Unlike the other planets, Earth's name comes from the Anglo-Saxon word "erda" meaning ground or soil. The Earth formed approximately 4.54 billion years ago and is the only known planet capable of supporting life. Additional facts: the Earth has one natural satellite (the Moon); it has a powerful magnetic field generated by its nickel-iron core that protects the planet; and it has the greatest density of all planets in the solar system.
Astronomy is one of the oldest sciences, with early civilizations like those in ancient China and at Stonehenge making careful records of astronomical phenomena. The field advanced significantly with Greek philosophers and scientists developing early mathematical models. Claudius Ptolemy created an influential geocentric model of the Solar System in his work The Almagest. Later, Nicolaus Copernicus developed the first heliocentric model placing the Sun at the center. Johannes Kepler then established his three laws of planetary motion, and Isaac Newton later formulated his law of universal gravitation and invented calculus, greatly advancing our understanding of astronomy.
This document provides information about the planet Saturn. It discusses Saturn's distance from the sun, diameter, temperature, rotation period, number of moons, composition and other key facts. It specifically mentions that Saturn is known for its prominent ring system, which was discovered by Christian Huygens in 1665 and that the Cassini Division, a gap within the rings, is named after Giovani Cassini who discovered it. The rings extend from 6,630 km to 120,700 km from Saturn's equator and are composed primarily of ice particles.
1) Early civilizations made observations of celestial objects to predict seasons and aid in navigation. The geocentric model proposed by Aristotle placed Earth at the center of the universe.
2) Planets were observed to move irregularly compared to other celestial bodies. Ptolemy proposed epicycles to explain retrograde motion within his geocentric model.
3) Copernicus suggested a heliocentric model where Earth and planets orbit the sun. Galileo's observations with a telescope supported this model.
4) Kepler developed his laws of planetary motion describing elliptical orbits with the sun at one focus. Newton later described universal gravitation explaining the forces at work.
This document discusses galaxies and our cosmic future. It begins by describing our own Milky Way galaxy and showing images of other galaxies, including spiral and elliptical galaxies. It then discusses galaxy luminosity functions and observations made using large telescopes. The document concludes by noting it was presented by Charles Liu at the American Museum of Natural History on September 23, 2011 and was about galaxies and our cosmic future.
- Dinosaurs lived on Earth for over 165 million years from the late Triassic period until the end of the Cretaceous period 65 million years ago. They varied greatly in size and appearance.
- Extinction occurs when a species can no longer adapt to environmental changes, leading to their death. A popular theory is that an asteroid impact caused the mass extinction that killed the dinosaurs. However, some evidence challenges this and suggests massive volcanic eruptions may have been responsible.
- The document discusses and provides evidence for both the asteroid impact theory and volcanic eruption theory for the cause of the dinosaur extinction. While the asteroid theory was widely accepted, newer evidence is increasingly supporting the volcanic eruption theory as well.
1. Astronomers detected a planet orbiting Proxima Centauri, the star closest to our sun, that is 1.3 times the mass of Earth and sits within the star's habitable zone.
2. Scientists from LIGO detected gravitational waves from the collision of two black holes over a billion years ago, confirming Einstein's theory of relativity.
3. Archaeological discoveries in Australia have shown that humans have inhabited the continent's interior for at least 49,000 years, 10,000 years longer than previously thought.
The document traces the development of scientific understanding of the solar system from ancient times to the modern era. It describes early geocentric models proposed by Anaximander and Ptolemy that placed Earth at the center. Later thinkers such as Aristarchus, Copernicus, and Galileo proposed heliocentric models with the Sun at the center. Kepler determined orbits were elliptical rather than circular, and Newton explained planetary motion through universal gravity. Edwin Hubble's discovery of an expanding universe led to the development of the Big Bang theory.
This document discusses biosignatures and the search for habitable exoplanets. It begins by reviewing Earth's biosignatures like oxygen, ozone, methane, and vegetation reflectance. It then explains that life exploits chemical energy gradients and metabolic reactions have an energy yield that can be quantified. The search for habitable worlds involves finding transiting exoplanets using ground and space telescopes to measure atmospheres. Direct imaging from space is also needed to find and characterize Earth analogs, with external occulters showing promise to block starlight. The overarching goals are to understand possible biosignatures on non-Earth worlds and find the most promising planets for atmospheric study.
The document discusses the history of Earth and how its environment has changed over billions of years. It describes how astronauts saw Earth as a single moment in time, and how the continents have shifted locations over hundreds of millions of years. It also explains how climate changes, like ice ages, have significantly altered Earth's surface and influenced human migration patterns in the past.
Spiral galaxies consist of a flat, rotating disc containing stars, gas and dust, with a central bulge. Elliptical galaxies are the most common type of galaxy and contain less gas and dust. Irregular galaxies have an irregular, chaotic appearance without distinct structure. Edwin Hubble proved in 1925 that the universe is expanding based on the relationship between galaxy distance and velocity.
- The Galileo probe explored Jupiter and its moons from 1995-2003, discovering evidence of subsurface oceans on Europa and volcanic activity on Io. It was the first spacecraft to fly by an asteroid and discover a moon orbiting an asteroid.
- Col. Eileen Collins was the first female shuttle commander, commanding missions STS-93 in 1999 and STS-114 in 2005. She has logged over 872 hours in space.
- The Mars Pathfinder mission in 1997 proved that a rover could be placed on Mars cheaply, sending back over 17,000 photos and 15 chemical analyses before ending in 1997.
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of pre-history: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy, and not completely disentangled from it until a few centuries ago in the Western World (see astrology and astronomy). In some cultures, astronomical data was used for astrological prognostication.
Ancient astronomers were able to differentiate between stars and planets, as stars remain relatively fixed over the centuries while planets will move an appreciable amount during a comparatively short time.
SideriusNuncius, also known as The Starry Messenger, was a 56-page scientific treatise published in 1610 by Galileo Galilei describing his astronomical observations using the newly invented telescope. In it, he described observing the surfaces of the moon, the Milky Way resolved into individual stars, and four of Jupiter's moons, which provided evidence against the Ptolemaic geocentric model of the universe. The work was important as the first scientific treatise addressing the telescope and its observations, demonstrating the scientific method and establishing observational astronomy as a field.
Galileo Galilei was one of the first people to make quality telescopes, which he used to make important astronomical discoveries such as the moons of Jupiter. He observed that Venus has phases and that Copernicus' heliocentric model of the solar system was more accurate than the geocentric model endorsed by the Catholic Church. Galileo openly challenged the Church's teachings, which led to conflict between science and religion. His discoveries and willingness to question established beliefs were pioneering and helped advance astronomy.
This document discusses the fine-tuned universe theory, which argues that the universe appears carefully designed to support life. It outlines several factors that must be precisely tuned for life, such as the organization of matter into atoms and precise mass relationships between subatomic particles. The document also reviews ideas about the origin of the universe, such as the Big Bang theory and biblical creation account. It provides illustrations of astronomical objects and facts about the immense scale of the universe.
1. The document discusses the history of astronomy from ancient Greek ideas of a geocentric universe to Copernicus' heliocentric model.
2. Key figures discussed include Ptolemy, who developed the geocentric model that dominated for over 1000 years, and Copernicus, who proposed placing the Sun at the center.
3. Kepler later determined that planets orbit in ellipses rather than circles, establishing his three laws of planetary motion.
This document provides a history of astronomy from ancient Greece to modern times. It describes how early Greek astronomers like Aristotle and Hipparchus made early observations of celestial objects but believed in a geocentric model where Earth is the center. Ptolemy later created an elaborate geocentric model, though Copernicus, Kepler, and Galileo provided evidence supporting a heliocentric model through observations, Kepler's laws of planetary motion, and Galileo's discoveries with the telescope. Newton later unified physics and astronomy by formulating the law of universal gravitation. Einstein then revolutionized our understanding of motion, space, and time through his theory of relativity.
This summary provides the high-level information from the lengthy document:
- The document discusses various topics related to nuclear energy and radioactive materials, including nuclear reactors, radioactive waste, and nuclear accidents.
- Specific events mentioned include the Chernobyl disaster, the Columbia space shuttle accident, and nuclear weapons accidents involving B-52 bombers.
- The document also references different types of nuclear facilities and technologies, such as nuclear power plants, research reactors, nuclear weapons, and medical uses of radioisotopes.
The document provides a timeline of important figures and events in astronomy from 3000 BC to 1727 AD. It summarizes the key contributions of figures like Aristarchus, who proposed the heliocentric model of the solar system; Ptolemy, who proposed the geocentric model; Tycho Brahe, who built important observatories; Galileo, who used telescopes to study astronomy; Kepler, who discovered the laws of planetary motion; and Isaac Newton, who discovered the law of universal gravitation and helped prove the heliocentric model. The timeline also notes the invention of the telescope in 1608, which greatly advanced the study of astronomy.
Este documento es una guía de compras publicada por el periódico El Universal en marzo de 2015. La guía contiene múltiples artículos sobre diferentes productos y servicios disponibles en ese mes para los lectores.
Minnesota Turns Away Hungry Kids from School Lunchendhunger
In Minnesota, 62,000 students from families making between $30,000 and $43,000 per year are eligible for reduced-price school lunches of $0.40 per meal. However, when some families cannot afford the co-payment, their children are either given an alternative meal like a cheese sandwich or have their lunch thrown straight into the trash in front of them. While four lunch employees were recently fired in Massachusetts for similar practices of denying food or shaming children, Minnesota law currently allows for students to be turned away if they do not pay the full co-payment amount.
1. The document discusses SignWriting, a writing system for sign languages that is supported by the Center for Sutton Movement Writing.
2. SignWriting uses a grid-based system of glyphs and can be encoded in Unicode, with some sign languages encoded in Plane 15 and others in Plane 16.
3. The Center for Sutton Movement Writing aims to provide standardized, stable, and free specifications for encoding various sign languages in fonts and Unicode for wide accessibility across operating systems and devices.
NRM International is a real estate services company established in 2008 that assists multinational companies with their real estate needs. They have over 100 employees from various countries working in their 12,000 square foot office in Gurgaon, India. NRM offers various real estate services including corporate and residential leasing, serviced offices and apartments, commercial and industrial property leasing, interior fit-outs and construction management. They pride themselves on transparency, efficiency, and world-class customer service.
The document describes a 4-day online SignWriting Symposium held from July 21-24, 2014 to celebrate 40 years of the SignWriting script. The symposium included over 50 presentations covering topics like SignWriting education, research, literature and software from participants in over 12 countries. Each day consisted of opening and closing sessions with moderators as well as multiple timed presentations in categories such as education, research, literature and software development related to SignWriting.
The document provides contact information for two Cambodia teams promoting World Capital Market 777 (WCM777). It lists mobile numbers, Skype, email addresses, and social media pages. It then shows numerous pages advertising WCM777's cloud services, digital products, investment opportunities, and multi-level compensation plan with bonuses for recruiting others and product sales. WCM777 is presented as a global financial network and new digital economy.
Evidence based Advocacy-Do's and Donts from Ilm Ideas on Slide Shareilmideas
The document discusses evidence-based advocacy for education reforms. It defines what constitutes evidence, such as data produced by the government or independent organizations. Evidence can inform policy actions like showing a reduction in block grants over time based on financial data. High quality, relevant evidence presented strategically to different stakeholders like politicians, bureaucrats and the public can help advocate for issues and create impact. The document emphasizes using government data and engaging non-confrontationally to productively support reforms through advocacy.
Background information about the International community of SignWriting users: their standards and projects.
Background information about the efforts to encode SignWriting in Unicode and the issues that need to be addressed.
Este documento es la guía de compras del periódico El Universal para el mes de julio de 2015. Contiene 8 páginas de recomendaciones y consejos para las compras del mes. La guía abarca diferentes categorías como electrónica, moda, belleza, deportes y ocio.
O documento discute o uso de hidrogéis na agricultura, destacando seus benefícios como condicionador de solo que melhora a retenção de água e nutrientes, reduz a lixiviação e aumenta a disponibilidade hídrica para as plantas. Vários estudos mostram que cultivos irrigados com hidrogéis necessitam de menos irrigação, têm maior crescimento e produtividade.
Explore how to identify, research and harness the niche or target market you want to work in.
Use the INSPIRE model to explore who your ideal client might be.
Explore simple ways to conduct market research in to your market.
This document discusses banking basics and choosing the right bank account. It explains that there are different types of accounts for different savings goals, like savings accounts, tax-free savings accounts, GICs and term deposits. When choosing a bank, you should consider factors like ease of access, simplicity, personalization and fees. The document provides a sample comparison of RBC and TD Canada Trust casual savings accounts, and notes the importance of reviewing bank statements regularly for accuracy. In the end, the author realizes through this research that TD Canada Trust may better suit their needs over their current bank, RBC.
1st Web Cross Channel Seminar - Fremtidens Forbruger (Asger)1st Web
The document discusses the changing consumer behaviors and the need for retailers to adopt an omni-channel approach. It notes that future generations of consumers are highly connected and move seamlessly between channels. To succeed, retailers need to provide consistent inventory, purchase options like buy online pickup in store, and customer service across all channels including mobile. Small pilot programs can help retailers test omni-channel strategies as consumers now expect to shop how they want, when they want, across any device.
Assessment of business plan session 24 28 november 2014 step by stepGodfrey Tshimauswu
1) The document outlines the step-by-step process for assessing business plans from 2015/16-2017/18 over five days from November 24-28, 2014 in all districts.
2) Session leaders from Social Work and Community Development will lead the process and ensure logistics and documentation are in place, and compile required reports. Panels will be set up to conduct assessments.
3) A daily and comprehensive final report will be compiled to track the number of NPOs assessed and recommended or not recommended for funding, along with any challenges.
To graduate with a Dogwood Diploma, students must complete certain core courses in subjects like English, math, science, and social studies. They need a minimum of 80 credits total, including 28 elective credits. Students also require 30 hours of volunteer or work experience and must complete the Grad Transitions program. To receive their diploma, students must pass provincial exams in certain subjects in grades 10 through 12.
Estimates of the Earth's age have varied widely over time, from thousands of years based on biblical interpretations to billions of years according to modern scientific dating methods. Early estimates relied on assumptions that could not be proven, while later experiments and calculations from physics and geology led to ages of millions to billions of years. Modern radiometric dating techniques have precisely measured the ages of the oldest rocks and minerals to establish the Earth formed approximately 4.5 billion years ago.
The document discusses different estimates of the Earth's age throughout history. It describes how Aristotle believed the Earth was eternal, while Bishop Ussher calculated the Earth's age as 4004 BC based on the Bible. Later scientists like Buffon, Helmholtz, and Lord Kelvin used experiments involving cooling of materials and the Sun's condensation to estimate ages of 75,000 years, 20 million years, and 20 million years, respectively. Lyell argued for a much older age based on geological records. Finally, Joly estimated the age as 80-150 million years based on salt accumulation in the oceans.
The document discusses methods that scientists use to determine the age of the Earth. It explains that radiometric dating is used to measure the decay of radioactive isotopes in rocks and minerals to estimate their age. While this provides a means to directly date some igneous rocks, most rocks cannot be directly dated and must be bracketed between dated materials. The document reviews several examples of dated rocks and materials. Though radiometric dating provides a framework, determining the exact age of the Earth remains an ongoing effort as techniques are refined.
The document discusses estimates of the age of the Earth and universe over time. Early estimates based on biblical interpretations placed the Earth's age at around 6000 years. The development of modern geology in the 18th century, led by James Hutton, established that geological processes occurred gradually over long periods, indicating a much older Earth. Radiometric dating techniques now provide precise measurements of billions of years for the Earth, meteorites, and universe based on the decay of radioactive isotopes.
This document provides an overview of geologic time and the development of the geologic time scale. It discusses how the time scale is divided into eons, eras, periods, and epochs based on changes in fossil records. Key principles that helped establish the time scale are described, such as superposition, horizontality, original lateral continuity, and biologic succession. Important scientists like Steno, Hutton, and Smith who contributed to understanding geologic time and stratigraphy are also mentioned. Absolute and relative dating methods are briefly introduced.
Time scale and plate techtonic theory-Geomorhology ChapterKaium Chowdhury
The document discusses the history and development of the geological time scale. It describes how Scottish geologist James Hutton advanced the theory of uniformitarianism in the late 18th century. It also mentions how British geologist William Smith discovered in the early 19th century that fossils are found in a definite order within sedimentary rock layers, which helped develop the geological time scale. The time scale provides a system to chronologically measure stratigraphy and relate it to time periods used by geologists and paleontologists. Radiometric dating indicates the Earth is approximately 4.57 billion years old.
Plate tectonic geologic time scale-Geomorhology ChapterKaium Chowdhury
The document discusses the history and development of the geological time scale. It describes how Scottish geologist James Hutton advanced the concept of uniformitarianism in the late 18th century, laying the foundation for the time scale. It also discusses how British geologist William Smith discovered in the early 19th century that fossils are found in a consistent order in rock layers, allowing them to be used to date the rocks. The development of radiometric dating methods in the 20th century further enabled geologists to assign absolute ages to rocks and develop the modern geological time scale.
The document provides an overview of a course on Earth science and the universe. It includes 12 lessons covering topics like mapping the seafloor, plate tectonics, earthquakes and volcanoes, the origin of the universe, the solar system, what we are made of, the extinction of dinosaurs, and whether life exists elsewhere. The first lesson introduces concepts of time, space, the structure of Earth, and the rock cycle. Subsequent lessons will explore these topics in more depth.
Geologists have divided Earth's history into intervals of geologic time based on significant events. The largest divisions are eons, which are subdivided into eras, periods, and epochs. The Precambrian eon covers most of Earth's history and saw the emergence of life. The Phanerozoic eon began 540 million years ago and is divided into the Paleozoic, Mesozoic, and Cenozoic eras, which are further subdivided and defined by important developments in life and changes in Earth's geology.
Chapter 2 Geology of Ethiopia and the Horn. The geology of Ethiopia includes rocks of the Neoproterozoic East African Orogeny, Jurassic marine sediments and Quaternary rift-related volcanism. Events that greatly shaped Ethiopian geology is the assembly and break-up of Gondwanaland and the present-day rifting of Africa.
This power point is important for all Ethiopian first year freshman universities students for the common course of Geography of Ethiopia and the Horn (GeES 1011), It is prepared on the bases of the module with additional explanations, important maps & explanatory images are included.
This power point mainly focuses on the geological history of the Earth in general and Ethiopia in particular. It is the best source of for all first year university freshman student of Ethiopia. if you are studying this course for A+ this material will definitely help. this material proven to be helpful by students of number of universities for the past four years.
Earth History 2: Changes in AtmosphereRobin Seamon
The document discusses the various factors that cause changes in Earth's atmosphere and climate over time. It explains that changes in one climate variable, such as the atmosphere, will affect others as they are all interconnected. The key factors identified are 1) biotic processes, 2) variations in solar radiation, 3) plate tectonics, 4) volcanic eruptions and large igneous provinces, 5) the cryosphere, 6) Milankovitch cycles, and 7) greenhouse gases. The document traces the history of scientific understanding of these climate change causes and how different evidence and techniques verified theories about ice age triggers being linked to orbital variations amplified by greenhouse gas feedbacks.
Fossils provide evidence about Earth's history by allowing geologists to correlate and date sedimentary rock layers. Fossils are the preserved remains or traces of ancient plants and animals. Index fossils, which existed for short periods of time, are particularly useful for correlating rock layers between locations. By comparing fossil assemblages, geologists can match rock layers of the same age, even when exposed in different areas. For example, fossils found in the Grand Canyon's Redwall Limestone layer match fossils found in Indiana and Kentucky, indicating all were deposited at the same time approximately 350 million years ago. Radiometric dating techniques like potassium-argon dating also provide numerical dates for when igneous and metamorphic rocks formed
This document discusses key concepts in relative dating of geologic materials. It introduces important figures like James Hutton and Charles Lyell who were influential in developing theories of geology. The key principles of relative dating are described, including the law of superposition, law of original horizontality, and law of cross-cutting relationships. The document also discusses using index fossils and unconformities to correlate rock layers between locations and determine their relative ages.
Marine geology is the study of the Earth below the oceans and seas. It examines the character and history of ocean floors and coastal areas. Major developments in marine geology include the HMS Challenger expedition in the 1870s which made the first systematic survey of ocean basins, and the Lamont-Doherty Geological Observatory founded in 1948 which advanced techniques like precision depth recording and piston coring. Deep-sea drilling projects from the 1960s-1980s using vessels like the Glomar Challenger confirmed theories of seafloor spreading and plate tectonics through ocean floor sampling and drilling.
This document provides an overview of geologic time and Earth's biological history. It begins with objectives to understand geologic change over Earth's history, factors that shaped the atmosphere and lithosphere, and creating a journal describing local physical features. The rest of the document details principles of the geologic time scale including superposition, cross-cutting relations, and index fossils. It provides a table of the geologic time scale with major life forms and tectonic events. Radiometric dating techniques like carbon dating are introduced for obtaining absolute ages. Major periods of Earth's history are summarized with changing life and environments.
_'2.12,13 Geologic Time and Relative Ages ' .pptxMOHAMADKAMAL35
Geologic time refers to the scale scientists use to measure Earth's history. It is divided into eons, eras, periods, and epochs based on evolutionary events in Earth's history recorded by fossils. Scientists use radioactive dating of rocks to determine absolute ages by measuring the decay of radioactive elements into daughter products. This has shown that Earth is approximately 4.6 billion years old. Key events in Earth's early history included the formation of the core, mantle, and crust, and the development of an atmosphere.
THE GEOLOGIC TIME SCALE OF THE HISTORY OF.pptxmargiebartolome
The document discusses the geologic time scale used to classify Earth's history. It is divided into eons, eras, periods, and epochs based on fossil and rock evidence. The two eons are the Precambrian and Phanerozoic. The Precambrian consisted of the Archean and Proterozoic eras when life first evolved. The Phanerozoic eon began when conditions allowed an explosion of life and is divided into the Paleozoic, Mesozoic, and Cenozoic eras. Scientists developed this time scale to bring order and meaning to Earth's 4.6 billion year history based on studies of rock formations and layers around the world.
Geologists used various dating methodologies involving ocean chemistry, erosion rates, and radiometric dating to determine that the Earth is billions of years old, contradicting earlier estimates by physicists like Kelvin of only millions of years based on cooling models. The discovery of radioactivity provided a major new heat source inside the Earth and revealed processes like radioactive decay that allowed for much older dating of rocks and minerals, establishing the age of the Earth to be over 4 billion years.
This document provides an overview of archaeology and studying the past. It discusses the differences between history and archaeology, with archaeology focusing on analyzing ancient objects and evidence uncovered through excavation. The document then discusses important archaeological techniques like excavation, mapping sites, screening soil, and carbon dating. It explains how archaeologists use these methods to better understand human origins and prehistory. Overall, the document serves as an introduction to the field of archaeology and how it can provide information about earlier periods of human existence.
The document discusses evidence that supports continental drift theory and plate tectonics theory. Alfred Wegener originally proposed continental drift in 1912 and provided evidence like matching coastlines, fossil and rock distributions, and coal deposits across continents. Plate tectonics improved upon this by explaining continental movement via the movement of rigid tectonic plates driven by convection currents in the mantle.
Natural selection occurs through a 5 step process: 1) Variation exists within populations, 2) Organisms compete for limited resources, 3) Organisms produce more offspring than can survive, 4) Genetic traits are passed to offspring, 5) Those organisms with traits most beneficial to survival and reproduction are more likely to survive and reproduce. The document also lists key terms related to biological evolution such as mass extinction, homologous structures, and vestigial structures.
This document provides an overview of the key concepts and evidence for the theory of evolution through natural selection. It explains that evolution means change over time as life adapts to survive obstacles. Charles Darwin observed variations between populations and that traits enabling survival and reproduction were selected for. His theory of natural selection and evidence like vestigial organs, homologous and analogous structures, and speciation have supported evolution as the foundation of biology.
The metric system is used by the scientific community and has basic units of length (meter), volume (liter), and mass (gram). It uses a metric staircase to represent prefixes for larger and smaller units, such as kilo, hecto, deka, centi, milli. To convert between units, move the decimal place left to go from smaller to larger units or right to go from larger to smaller units.
The document discusses the Cretaceous-Tertiary (K-T) extinction event that occurred 65 million years ago. It notes that this was a mass extinction where over 50% of all species died, including non-flying dinosaurs, many marine invertebrates, flying pterosaurs, mosasaurs, and plesiosaurs. The main proposed cause is the Chicxulub impact crater, evidence for which includes the rare metal iridium and shocked quartz found in K-T boundary layers worldwide. The impact would have released huge amounts of energy, darkened skies for years with dust and ash, and caused global climate changes that disrupted ecosystems.
The document describes the four main layers that make up the Earth - the crust, mantle, outer core, and inner core. The crust is the top-most layer where life exists, ranging from 5-25 miles thick. Below is the mantle, a semi-liquid layer 3000 km wide that causes convection currents moving the continents. Deepest are the solid inner core and surrounding liquid outer core, both composed primarily of iron.
Rocks are classified into three major groups: igneous rock forms when magma or lava cools, sedimentary rock forms when particles are pressed together, and metamorphic rock forms when heat and pressure change any existing rock.
The document discusses the three main types of rocks: sedimentary, metamorphic, and igneous. Sedimentary rocks are formed from the compression of sediment layers over time. Metamorphic rocks were once sedimentary or igneous rocks, but were changed by heat and pressure. Igneous rocks form either underground from cooled magma or above ground from volcanic eruptions. Examples of each rock type are also provided.
The rock cycle describes how rocks are continuously transformed between three main types - igneous, sedimentary, and metamorphic rocks - through geological processes such as erosion, deposition, burial, melting, and crystallization. Igneous rock is weathered into sediment and deposited to form sedimentary rock, which is then buried and altered by heat and pressure into metamorphic rock. Metamorphic rock can be melted into magma and erupt as new igneous rock, restarting the cycle.
Geological evolution refers to gradual changes in the Earth over time, including through plate tectics. Plate tectonics involves large pieces of the Earth's outer layer called plates that move and change position. One aspect is continental drift, where the shifting plates cause continents to gradually change location. Scientists believe the continents were once joined in a supercontinent called Pangaea. Relative dating uses rock layers and fossils to determine the age of rocks, such as the law of superposition that the top layer is youngest and bottom oldest.
Rocks form in different ways and are classified based on their composition and how they are formed. The rock cycle shows how rocks continuously change over time through geological processes like weathering, erosion, deposition, and metamorphism. Scientists use various methods to determine the relative and absolute ages of rocks, including analyzing rock layers and fossils. Index fossils in particular allow scientists to relatively date rock layers based on the period of time specific fossils existed.
The document discusses the Geological Time Scale which is used to divide Earth's history into eras, periods and epochs based on fossil and rock evidence. It describes the major eras - Precambrian, Paleozoic, Mesozoic and Cenozoic - along with key environmental conditions and lifeforms that existed during each era, noting major extinction events. The timeline shows how life on Earth has evolved and changed dramatically over its approximately 4.5 billion year history.
Earth's history can be determined through relative and absolute dating methods. Relative dating uses the law of superposition to determine the relative age of rocks and fossils by their position in rock layers, with lower layers being older. Absolute dating provides specific numerical ages by using radiometric dating techniques to measure the decay of radioactive elements. Together these methods are used to construct geologic timescales that reveal the order and ages of events in Earth's development.
Alfred Wegener proposed the theory of continental drift in 1912, which stated that approximately 250 million years ago, all the continents were joined together in a supercontinent called Pangaea. Over time, the continents gradually drifted apart to their current locations. The key evidence for continental drift included the matching coastline shapes of continents, the presence of matching fossil distributions on different continents, identical rock patterns found across continents, and evidence of past shared climates from fossil evidence.
Scientists study Earth's past environments and lifeforms by examining fossils. Fossils form when organisms are buried and their remains are replaced with minerals over time. There are different types of fossils including molds, casts, petrified remains, preserved fossils like those trapped in ice or amber, carbonized remains, and trace fossils like footprints. Together, the analysis of these various fossil types provides evidence about ancient organisms, environments, behaviors and evolutionary relationships.
Sanatan Vastu | Experience Great Living | Vastu ExpertSanatan Vastu
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A375 Example Taste the taste of the Lord, the taste of the Lord The taste of...franktsao4
It seems that current missionary work requires spending a lot of money, preparing a lot of materials, and traveling to far away places, so that it feels like missionary work. But what was the result they brought back? It's just a lot of photos of activities, fun eating, drinking and some playing games. And then we have to do the same thing next year, never ending. The church once mentioned that a certain missionary would go to the field where she used to work before the end of his life. It seemed that if she had not gone, no one would be willing to go. The reason why these missionary work is so difficult is that no one obeys God’s words, and the Bible is not the main content during missionary work, because in the eyes of those who do not obey God’s words, the Bible is just words and cannot be connected with life, so Reading out God's words is boring because it doesn't have any life experience, so it cannot be connected with human life. I will give a few examples in the hope that this situation can be changed. A375
A Free eBook ~ Valuable LIFE Lessons to Learn ( 5 Sets of Presentations)...OH TEIK BIN
A free eBook comprising 5 sets of PowerPoint presentations of meaningful stories /Inspirational pieces that teach important Dhamma/Life lessons. For reflection and practice to develop the mind to grow in love, compassion and wisdom. The texts are in English and Chinese.
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The Hope of Salvation - Jude 1:24-25 - MessageCole Hartman
Jude gives us hope at the end of a dark letter. In a dark world like today, we need the light of Christ to shine brighter and brighter. Jude shows us where to fix our focus so we can be filled with God's goodness and glory. Join us to explore this incredible passage.
The forces involved in this witchcraft spell will re-establish the loving bond between you and help to build a strong, loving relationship from which to start anew. Despite any previous hardships or problems, the spell work will re-establish the strong bonds of friendship and love upon which the marriage and relationship originated. Have faith, these stop divorce and stop separation spells are extremely powerful and will reconnect you and your partner in a strong and harmonious relationship.
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The Book of Ruth is included in the third division, or the Writings, of the Hebrew Bible. In most Christian canons it is treated as one of the historical books and placed between Judges and 1 Samuel.
The Enchantment and Shadows_ Unveiling the Mysteries of Magic and Black Magic...Phoenix O
This manual will guide you through basic skills and tasks to help you get started with various aspects of Magic. Each section is designed to be easy to follow, with step-by-step instructions.
2. Outline of Talk
Part 1. The Age of the Earth
Practical: Saltiness of Ocean
Part 2. The History of the Earth
Practical: Dawn of a New Age
Part 3. Radiometric dating
4. Age of the Earth (2): The Bible
4004 BC
• In 1654 Bishop Ussher calculated that the
Earth was created in 4004 BC
• He got this figure using evidence from the
Bible and other Middle Eastern literature
• The date became so popular that it was
printed with the Book of Genesis
Bishop Ussher
(1581-1656)
en.wikipedia.org/wiki/Image:Ussher.jpg
en.wikipedia.org/wiki/Image:Genesis.jpg
5. Age of the Earth (3): Experiments
Comte de Buffon
(1707-1788)
• In 1760, Buffon
measured the cooling
time of red-hot iron
balls of different sizes
• He scaled up to the
size of the Earth
(75,000 years to cool)
http://en.wikipedia.org/wiki/Image:
Buffon_1707-1788.jpg
One of
Buffon’s iron balls
6. Age of the Earth (4): The Sun
http://en.wikipedia.org/wiki/Image:
Hermann_von_Helmholtz.jpg
http://upload.wikimedia.org/wikipedia/en/9/93/Cropped_Earth_with
NG
Hermann von
Helmholtz
(1821-1894)
• In 1858, calculated the time it would
take for the sun to condense to
present diameter from gas nebula
(around 20 million years)
7. Age of the Earth (5): More Physics
http://en.wikipedia.org/wiki/Image:Lord_
Kelvin_photograph.jpg
Lord Kelvin
(1824-1907)
• In 1862, Lord Kelvin
assumed that Earth
originally had a
temperature of 7000°F
• Knew geothermal
gradient (1°F/50 ft)
• Calculated cooling age
(20 million years)
Geothermal
gradient
8. Age of the Earth (6): Geology
Charles Lyell
(1797-1875)
• Sediment accumulates at the same rate
today as in the past so Earth must be really
ancient to account for geological record
(hundreds of millions of years)
http://en.wikipedia.org/wiki/Image:Charles_Lyell.jpg http://en.wikipedia.org/wiki/Image:Colorado_River_edit.jpg
9. Age of the Earth (7): Evolution
Lord Kelvin’s “views on the recent age of the world have been
for some time one of my sorest troubles” (Darwin to Wallace)
• In 1869, Thomson
argued that there was
not enough time
for Darwin’s evolution
by natural selection
http://en.wikipedia.org/wiki/Image:
Lord_Kelvin_photograph.jpg
Charles
Darwin
Lord Kelvin
http://en.wikipedia.org/wiki/Image:
Darwin aged 54.jpg
10. Age of the Earth (8): Sea Salt
• In 1899, John Joly calculated the Earth’s
age using the saltiness of the ocean
(80-150 million years)
• How much salt was in the Ocean?
• How much did rivers add each year?
Obituary Notices of F.R.S., 1, 260 (1933)
John Joly (1857-1933)
http://www.bigfoto.com/miscellaneous/photos-16/index.htm
salt
crystals
11. Age of the Earth (9): Assumptions
• All these estimates
were based on
assumptions that
couldn’t be proven
12. Practical Exercise 1
Calculating the Age of the Earth using
the Saltiness of the Ocean
http://www.bigfoto.com/miscellaneous/photos-16/index.htm
16. Geological History (4): Maps
William Smith
(1769-1839)
http://en.wikipedia.org/wiki/Image:
William_Smith.g.jpg
The Map that
changed the World
http://en.wikipedia.org/wiki/Image:
Geological_map_of_Great_Britain.jpg
Some of
Smith’s fossils
http://en.wikipedia.org/wiki/Image:Smith_fossils2.jpg
17. Geological History (5): Fossils
Cuvier
• Cuvier showed that
some animals had
gone extinct
• Lyell used the
proportion of living
fossils to divide up
geological time
• Older rocks contained
more extinct types
than younger rocksCharles Lyell
(1797-1875)
Georges Cuvier
(1769-1832)
en.wikipedia.org/wiki/Image:Georges_Cuvier.jpg en.wikipedia.org/wiki/Image:Charles_Lyell.jpg
18. Geological History (6): Stratigraphy
A tug-of-war as rocks got sorted into geological periods in the
new science of stratigraphy
commons.wikimedia.org/wiki/Image
:Adam_Sedgwick.jpg
en.wikipedia.org/wiki/Image:Roderick
_Murchison.jpg
en.wikipedia.org/wiki/Image:Geological_map_of_Great_Britain.jpg
MurchisonSedgewick
19. Geological History (7): Periods
Carboniferous
en.wikipedia.org/wiki/Geologic_time_scale
Cambrian
Ordovician
Silurian
Devonian
Permian
Triassic
Jurassic
Cretaceous Tertiary
Quaternary
20. Geological History (8): The Column
Geological Time: Eons, Eras, Periods and Epochs
http://en.wikipedia.org/wiki/Geologic_time_scale
21. Geological History (9): Example
Impact
http://en.wikipedia.org/wiki/Image:KT_boundary_054.jpg
http://en.wikipedia.org/wiki/Image:Impact
_event.jpg
en.wikipedia.org/wikiImage:Palais_de_la_Decouvert
e_Tyrannosaurus_rex_p1050042.jpg
en.wikipedia.org/wiki/Image:Tyrannosaurus_BW.jpg
Extinction
Cretaceous
Paleogene
22. Practical Exercise 2
The Anthropocene: The Dawn of a New Age?
http://en.wikipedia.org/wiki/Image:Midtown_Manhattan_Oct_2007.jpg
New York skyline
23. Radiometric dating (1): Discovery
http://en.wikipedia.org/wiki/Image:
Henri_Becquerel.jpg
Henri Becquerel
(1852-1908)
• In 1896, Discovery of radioactivity paved
the way for the precise dating of events
in the geological record
24. Radiometric dating (2): Decay
en.wikipedia.org/wiki/Image:Alpha_Decay.svg
• Radioactive ‘parent isotopes’ spontaneously emit protons and
neutrons and decay into ‘daughter isotopes’
• E.g., Uranium-238 decays into Lead-206
25. Radiometric dating (3): Half life
• The rate of decay from parent to daughter isotope depends on
its half life. The half life is the amount of time needed
for half the parent isotope to decay to daughter isotope
Half life: 0
Half life: 1
Half life: 2
Linear
Exponential
26. Radiometric dating (4): Clocks
• Different radioactive isotopes have different half lives
• Isotopes with long half lives are useful for dating old rocks. It is
important to use the right tool for the right job
Decay series Half life
40
K to 40
Ar 1250 Ma
147
Sm to 143
Nd 1060 Ma
235
U to 207
Pb 704 Ma
238
U to 206
Pb 4468 Ma
14
C to 14
N 5370 years
Geological
timescales
Archaeology
27. Radiometric dating (5): Pioneers
Arthur Holmes
(1890-1965)
Ernest Rutherford
(1871-1937)
en.wikipedia.org/wiki/Image:
Ernest_Rutherford2.jpg
en.wikipedia.org/wiki/Image:
A Holmes.jpg
• Rutherford figured out a
technique to date the age
of rocks in 1904
• Holmes developed this
kind of ‘radiometric dating’
still further.
• In 1913 Holmes dated
some rocks from Ceylon
to 1600 million years
30. Radiometric dating (8): Meteorites
• Radiometric age of meteorites
date the formation of the
Solar System and Earth
(4550 million years old)
en.wikipedia.org/wiki/Image:Canyon-diablo-meteorite.jpg
http://upload.wikimedia.org/wikipedia/commons/0/00/Crab_Nebula.jpg
Crab Nebula
Canyon Diablo meteorite
Presenter notes: Planet Earth is more than 4500 million years old (that is, 4.5 billion years old). Such a vast abyss of time is hard to comprehend. When geologists talk about this kind of ‘deep time’ they use the term geological time to distinguish geological ages from the shorter timescales involved in human history. In this talk we will learn about geological time and how geologists first discovered the deep history of our planet. Background notes: One way to convey the vastness of geological time is to use the analogy of a 24 hour clock. If the earth was formed at midnight, then life did not appear until 06:00, the first animals and plants only made it onto land as late as 22:00, and humans evolved about 23:59, less than one minute before midnight.
Presenter notes: There are three parts to this talk. In the first part we will learn about early ideas concerning the age of the Earth. It was through trying to work out the age of the Earth that geological time was first discovered. In Exercise 1, you will have a go at calculating the age of the Earth using a nineteenth century method (now considered incorrect) based on the saltiness of the ocean. In the second part we will learn about how geologists divide up geological time into different eons, eras, periods and epochs based on fossils and other evidence. This is important for sorting out the order that events occurred through the history of the Earth. In Exercise 2, you will investigate whether humans have altered the planet to such an extent that we are now entering a new geological age. In the final part, we will explore how a twentieth century technique called radiometric dating revolutionized our understanding of the age of the Earth. As a result we will see how geologists can now precisely date events like the extinction of the dinosaurs rather just talk about the relative order that events occurred.
Presenter notes: So let’s begin by looking at early ideas about the age of the Earth. As we do so, its worth reminding ourselves that this fundamental question did not arise for many of the earliest societies. In Hindu thought and especially in the classical Greek world most people thought the Earth was eternal. For Greek philosophers like Aristotle time was a circle and there was no beginning or end. To him, the question of the age of the Earth was entirely irrelevant.
Presenter notes: In a sense, thinking about the age of the Earth began with birth of Judaism and the belief in a God that had created the world out of nothing. Following the rise of Christianity, interest in God’s creation increased further and most early attempts to establish the age of the Earth were based on the Bible. Scholars used the chronological records in the Bible, together with dates found in other Middle Eastern literature to establish the amount of time between the creation of Adam and the birth of Jesus. The first person known to attempt this kind of calculation was Theophilus of Antioch in AD169 but other notable attempts were made by the physicist, Sir Isaac Newton (1643-1727), and most famously by Bishop James Ussher (1581-1656). All these calculated dates were roughly the same (as they relied on the same method) but Ussher’s date of 4004 BC became so popular that it was printed as a marginal note in the Book of Genesis. Background note: Although often ridiculed today, in their time, these Biblical calculations were the height of good academic scholarship (see Stephen Jay Gould, "Fall in the House of Ussher." Natural History 100 (November 1991): 12-21 ). That said, creationist groups that promote a Young Earth today (often citing Ussher’s 4004 BC) are examples of bad scholarship. They ignore or distort the advances in understanding that have accumulated since Ussher’s day.
Presenter notes: Following the Renaissance and the birth of modern science, thoughts about the age of the Earth moved away from Biblical evidence. Instead it became popular to rely on the new science of Physics for answers. In 1760, a French naturalist called Comte de Buffon, aka Georges Louis Leclerq (1707-1788), hypothesized that the Earth had originated as a fiery ball after a comet had collided with the Sun. He experimented by heating iron balls of different sizes and then measured how long they took to cool down. Using this information, he scaled up to the much larger size of the Earth and predicted that would have taken about 75,000 years for the planet to cool down from a molten state. This seemed like an eternity to the people of Buffon’s day who were used to hearing that the Earth was only 6,000 years old based on the Bible.
Presenter notes: By the mid-nineteenth century, physicists were proposing ingenious new ways to date the age of the Earth. In 1858, a German scientist, Hermann von Helmholtz (1821-1894) started to think about the origin of the Sun. He thought that the Sun had formed by the contraction of a nebula of gas and dust. He calculated that if would have taken about 20 million years for the Sun to shrink to its current diameter and brightness. Therefore the Earth could be no younger than 20 million years.
Presenter notes: In 1862, William Thomson (1824-1907), aka Lord Kelvin, tried a different approach based on Physics. Kelvin knew that the temperature of the Earth increased by 1 degree of Fahrenheit for every 50 feet you went into the ground. He also assumed that the temperature of the early Earth had been around 7000 degrees of Fahrenheit when molten. Applying his knowledge of how fast heat is conducted through rocks he calculated that it would have taken around 20 million years for the Earth to cool to its present state. The fact that two independent approaches had arrived at roughly the same answer gave Physicists a lot of confidence that they were right. However, as we will see later their age calculations were quite wrong because they assumed that the Earth was steadily losing heat. In fact the discovery of radioactivity in the early twentieth century showed that the Earth was also producing some heat. Therefore the Earth must have been much older than allowed by Lord Kelvin’s calculations
Presenter notes: One group of scientists who had a hunch that Lord Kelvin’s age of the Earth was far too young were the geologists. The geologist Charles Lyell (1797-1875) thought that the key to understanding the age of the Earth might lie in the way that mountains slowly erode down. Lyell thought that the rate at which the erosion and deposition of sediment occurs had stayed more or less constant through geological time. If he was correct and ‘the present was the key to the past’ then it must have taken many hundreds of millions of years to form the vast repository of sediment seen in the geological record, much longer than the ages allowed by Lord Kelvin and the Physicists. Background notes: Through the nineteenth century there was many attempts to use this approach to estimate the age of the Earth. To do this calculation one needed to know the total thickness of sediment on the Earth’s surface and also the average rate at which sediment accumulates today. However, it proved enormously difficult to get hard numbers for either of these figures. The main problem was than sediment accumulates at widely differing rates in different environments so in the deep sea a single millimetre of mud might take a thousand years to build up whereas in an active river channel, a metre of sand might be deposited in a few hours. These problems made geological estimates of the age of the Earth seem very inaccurate compared to the precise numbers put forward by the Physicists.
Presenter notes: One nineteenth century scientist who anxiously followed the debate about the age of the Earth was Charles Darwin (1809-1882). Darwin had argued in 1859 that life had evolved through small incremental changes by a process called natural selection. As he envisaged that this process acted extremely slowly, the Earth had to be really really old; in fact much older than Kelvin’s calculations allowed. Lord Kelvin repeatedly attacked Darwin’s theory of evolution and, in 1869, Darwin confided to his supporter Alfred Wallace that Kelvin’s “views on the recent age of the world have been for some time one of my sorest troubles”. Evolution by natural selection was an enormously controversial idea in the nineteenth and wasn’t widely accepted by the scientific community until the 1920s. If the Earth was relatively young, as Kelvin argued, then there simply wasn’t enough time for the kind of evolutionary change that Darwin proposed.
Presenter notes: At the end of the nineteenth century, a new approach to understand the age of the Earth was put forward by the Irish geologist, John Joly (1857-1933). This approach relied on Edmund Halley’s work on the saltiness of the ocean. Halley (who is more famous for his comet) had earlier shown how salt is weathered out of rock on land and carried by rivers to the oceans, where it gradually builds up. In 1899, Joly argued that if you knew how salt was in the ocean and you knew how much salt was being added each year by rivers then you could work out the time when there was no salt in the the oceans, and hence the age of the Earth. After several attempts the figure he finally came up with was an age ranging between 80-150 million years. Unfortunately, what Joly didn’t realize is that salt doesn’t simply accumulate in the oceans over time. Rather there are geological processes that are constantly taking salt out of the oceans. Hence, Joly’s age was far too low.
Presenter notes: As we have seen, all the methods put forward in the nineteenth century to figure out the age of the Earth relied on certain assumptions that couldn’t necessarily be proven. Kelvin assumed the Earth was steadily cooling from a molten state, Lyell assumed that the rate of sedimentation had been constant through history, and Joly assumed the saltiness of the ocean was being added to year after year. This meant that all these estimates of the age of the Earth were highly uncertain.
Presenter notes: To illustrate some of the problems and uncertainties in nineteenth century calculations of the age of the Earth, let’s look at an example. As we have seen, John Joly tried to determine the age of the Earth using the saltiness of the ocean. In Exercise 1 we will attempt to reproduce Joly’s calculation and think about why it was flawed.
Presenter notes: So far we’ve looked at early attempts to determine the age of the Earth, let’s now consider how other scientists were trying to work out its history. The term geological history refers to the sequence of historical events from the formation of the Earth to the present day. One of first people to try and understand the history of our planet was a Danish priest called Nicolas Steno (1638-1686). In 1669 he argued that sediment gradually built up on the sea floor as layers which are both laterally continuous and horizontal. The sediments at the bottom of the pile are the oldest and the sediments at the top are the youngest. Steno showed that in much the same way that the pages of a book are read from left to right, the history of the Earth must be read from bottom to top in a layered succession of rocks. Background note: Steno’s insight that sediments accumulate in continuous horizontal layers is known as the Principle of Horizontality and the Principle of Lateral Continuity. His insight that the oldest sediments are at the bottom and the youngest at the top is known as the Principle of Superposition. These three principles are fundamental to understanding the order that events occurred through Geological Time.
Presenter notes: A century later, Abraham Werner (1749-1817), a mining engineer from Saxony, started to apply some of Steno’s principles to understand the history of the Earth. He thought that all the Earth’s rocks had been deposited from a worldwide ocean (think Noah’s Flood in the Bible). This idea was later dubbed ‘Neptunism’ after the Roman god of the sea (Neptune). Werner thought that crystalline rocks like granite were the first to form in this worldwide ocean while the most recent sands and muds on top had been deposited by rivers after the great sea had withdrawn. On this basis, Werner’s supporters divided the Earth’s rocks into four groups – Primary, Secondary, Tertiary and Quaternary – representing four intervals of geological time. Background notes: Two Wernerian terms are still widely used today for the youngest rocks on our planet: Tertiary and Quaternary
Presenter notes: Hot on the heels of Werner came another influential geologist called James Hutton (1726-1797). In the late eighteenth century, Hutton realized that there were ‘big gaps’ in the geological record of time. At several places like Siccar Point in Berwickshire, Scotland, Hutton’s noticed beds of layered rocks that stood on their end overlain by other layered rocks that dipped away at a shallow angle. Hutton was quick to realize what this meant. In the real world, sediment is not deposited continuously. Rather through convulsions of the Earth’s crust, sediments laid down as horizontal layers in the sea might be pushed up to form mountains. The layers might then be tilted at an angle and partly eroded away before new horizontal layers accumulated on top. Hutton’s name for this kind of angular contact between two sets of sedimentary layers was an unconformity. In the time between the formation of the lower and upper layers of rocks, a mountain had been born and eroded down. This would have taken tens of millions of years. Therefore the unconformity represented a massive time gap in the geological record. Hutton referred to this phenomenon as ‘the abyss of time’.
Presenter notes: At the turn of the nineteenth century, ‘maps’ followed ‘gaps’ in the discovery of geological history. In Britain railways and canals were being constructed all over the place. More than ever before, rocks were being exposed all over the country. William Smith (1769-1839) was a surveyor who saw more than his fair share of rocks. He realized that sequences of different rocks occurred in the same order in different places. To be sure that a rock type in one place was the same as a rock type in another place, he compared the fossils that they contained. Soon he started to draw maps of where the different rock strata occurred and by 1815 he had produced a complete geological map of Britain. Building on the insights of Steno, Werner and Hutton, William Smith’s map showed the relative order in which the rocks of Britain formed and whether there were any big time gaps within the succession. For the first time, the geological history of a whole country was known. Background notes: Simon Winchester’s book titled “The Map That Changed The Whole” (HarperCollins 2002) give a lively introduction to William Smith and his geological map. Poor old Smith had the intellectual rights to his map stolen and never really received due reward for his remarkable achievements.
Presenter notes: As we have just seen, William Smith used fossils to check that the age of rocks in one area was the same at the rocks in another. But why should rocks of different ages contain the remains of different life forms? It fell to two other scientists, Georges Cuvier (1769-1832) and Charles Lyell (1797-1875) to answer this question and in doing so discover the concept of extinction. Cuvier was a French naturalist. In 1796 he studied remains of fossil and living elephants. He convincingly showed that animals like the woolly mammoth had gone extinct. This was a pretty radical idea because up to that point people thought extinction was impossible. After all, if God’s creation was perfect why would He let species like the mammoth die out? A little later in 1828, Lyell studied fossil seashells in Tertiary rocks in France. He showed that the oldest rocks contained mostly extinct shells while the youngest rocks contained shells similar to those living today. He divided up these Tertiary deposits into three epochs which he named, from oldest to youngest, the Eocene, Miocene, and Pliocene. At last here was an explanation as to why the rocks of different time periods contained distinctively different types of life forms Background notes: Eocene means “Dawn of the Recent” by which Lyell meant that the rocks contained remains of life distinctive of early times. Miocene means “Less Recent” by which Lyell meant that the rocks contained remains of life that were less similar than those present today. Pliocene means “More Recent” by which Lyell meant that the rocks contained remains of life that were more similar to those present today.
Presenter notes: Although William Smith had worked out a general geological history of Britain in 1815, that record still was only vaguely understood. In the mid-nineteenth century British geologists started to argue amongst themselves about the precise order in which the strata were arranged. One famous argument was between Adam Sedgewick (1785-1873) and Roderick Murchison (1792-1871). Both these men mapped the rocks in Wales, which were thought at that time to be the oldest rocks that contained fossils. Both wanted to be the first to name this ancient geological period. Sedgewick proposed the name Cambrian for the the geological period represented by his rocks in Central Wales. Murchison proposed the name Silurian for the the geological period represented by his rocks in North Wales. As the Cambrian and Silurian strata overlapped, Murchison wanted all of Sedgewick’s Cambrian to be included in his Silurian. Based on the fossils they contained, Murchison didn’t think there was much age difference between the two time periods. Murchison and Sedgewick had a real tug-of-war over the rocks of Wales and afterwards didn’t speak to each other for years to come. Eventually, in 1879, Charles Lapworth (1842-1920) sorted out the Welsh problem. He carried on using the names, Cambrian and Silurian, but re-named the overlapping beds in the middle as the Ordovician. Hence the oldest rocks in Britain that contain ‘visible fossils’ comprise three geological periods which are, from oldest to youngest, the Cambrian, Ordovician, and Silurian. The science of mapping rocks and working out their age relative to one another became known as stratigraphy
Presenter notes: It wasn’t just in Wales that disputes raged about the naming and relative age of different rock types. Throughout the nineteenth century, geologists all over Europe were describing the geological record, eager to be the first to name the different geological periods. The Devonian Period was named after rocks in Devon that were a little younger than Sedgewick’s Silurian. The Carboniferous Period was named after the coal-rich rocks in Yorkshire. The Jurassic Period was named after the rocks of the Jura Mountains of Switzerland, and so on.
Presenter notes: Eventually, as geological mapping continued apace, the geological column became sorted into a series of orderly and ever more finely sliced divisions. The largest of these divisions is known as an Eon, which in turn is subdivided into Eras, Periods and Epochs. Hence, we can talk of Charles Lyell’s oldest tertiary rocks of France as belonging to the Eocene epoch of the Paleogene Period of the Cenozoic Era of the Phanerozoic Eon. The subdivision of the geological record continues today overseen by the International Commission on Stratigraphy.
Presenter notes: Before we finish this look at Geological History, its worth thinking about exactly how geologists decide to place the boundary between one geological period and the next. Boundaries are usually positioned where there is an abrupt change in the kinds of fossils in the rock or a change in the ancient climate or environment. To give an example, let’s take a look at the Cretaceous-Paleogene boundary. One of the most important changes that happened at the end of the Cretaceous Period is that dinosaurs like Tyrannosaurus rex went extinct. However, it wasn’t just the dinosaurs that disappeared at this time but a whole load of other animals and plants as well. Geologists now believe this ‘mass extinction’ was caused by a giant meteorite colliding with the Earth. This event led to a dramatic change to the kinds of animals and plants on the planet and therefore can be recognized in rock successions all over the world. We’ll further explore how geologists divide up geological time in the next practical exercise.
Presenter notes: We’ve just seen how geologists divide geological time into eons, eras, periods and epochs. The boundary between two geological intervals is always marked by some recognizable change in the ancient environment, climate or life. In the Cretaceous-Paleogene example we’ve just discussed, the boundary is marked by a mass extinction event probably triggered by a huge meteorite impact In this practical we will consider whether we have just crossed the threshold of a new geological interval. Today, human beings are radically altering the face of the planet including its climate and ecosystems. We’ve build gigantic megacities like New York and Shanghai and farm more than a third of the Earth’s surface. All this raises an interesting question. Have we changed our planet sufficiently to have embarked on a new geological age? Some geologists think we have and have called this new epoch, The Anthropocene. All the information you need to complete Practical Exercise 2 is found on the handout sheet and you should spend about 35 minutes on this task.
Presenter notes: So far we have looked at early ideas about the age of the Earth and how geologists gradually discovered the relative order that events had occurred through the history of the Earth. However what was still unknown was the precise age of each geological period while the total of the age of the Earth was still uncertain. In 1896, the discovery of radioactivity by Henri Becquerel (1852-1908) was to begin answering these questions and revolutionize our understanding of geological time.
Presenter notes: Radioactivity refers to the way that some chemical isotopes are inherently unstable and slowly lose mass by emitting particles called protons and neutrons (radiation). In the diagram, the original isotope, or parent isotope, has decayed into a daughter isotope by emitting alpha radiation. An example of this phenomenon in nature is the way that Uranium-238 spontaneously decays into Lead-206.
Presenter notes: The rate at which a parent isotope decays into a daughter isotope depends on its half life. The half life is the amount of time it takes for half of the parent isotope to decay into the daughter isotope. To illustrate this, look at the image on the left. If we imagine that the Red Isotope decays to the Green Isotope with a half life of one hour, how much of the Red Isotope will be left after two hours? The answer is, of course, that after 1 hour there will be 50% left, and after 2 hours there will be 25% left, and so on. Because of this repeated halving, the rate of decay of the parent isotope is said to be exponential. To illustrate this look at the image to the right where the exponential decay of an isotope is shown in blue. Compare it with a linear rate of change as seen, for example, when sand runs through an hour glass. The amount of sand in the upper vessel of an hour glass is eventually exhausted, but the exponential decay of an isotope means the parent isotope is never completely used up.
Presenter notes: Different isotopes have different half lives. For example, it takes 4486 million years to convert half of the Uranium-238 in a sample to Lead-206 but only 704 million years to convert half of the Uranium-235 in a sample to Lead-207. If you know the proportion of parent to daughter isotope in a rock sample and you know the half life of the isotope then you can work how long ago there was only parent isotope present, and hence the age of the rock. It works a bit like a natural clock. To illustrate this look at the diagram on the right. Here the relative proportion of different isotopes have been measured in a rock sample. Half of the Uranium-238 has been converted to Lead-206 (1 half life) but 98.8% of the Uranium-235 has decayed to Lead-207 (6.4 half lives). This tells us that the rock is around 4500 million years because one half life of Uranium-238 equals 4468 million years and 6.4 half lives of Uranium-235 indicates a similar age. Most of the isotopes shown in the list on the left have half lives that last hundreds of million years. Consequently they are good for measuring the age of really old thing (i.e. the geological timescale). However, C-14 decays in N-14 with half life of only 5370 years. After about eight half lives there is too little parent isotope left in the sample to measure. Consequently C-14 can only be used to date thing up to about 40,000 years old (8 half lives) and is only used in Archaeology.
Presenter notes: The first person to try and use radioactive decay as a natural clock to date rocks was the physicist Ernest Rutherford. In 1904 he named this technique radiometric dating. Unfortunately, Rutherford ran into all sorts of problems with his geological dating and eventually gave up. However, his work was followed up by a bright young student called Arthur Holmes. In 1913, when Holmes was only 23, he dated some rocks from Ceylon to be more than 1600 million years ago. This age was much older that the estimates of the age of the Earth made by nineteenth century physicists like Lord Kelvin and caused a great deal of controversy. But Holmes’s work was so good that there was no getting round the matter and eventually geologists had to get used to the idea that the Earth was billions of years old, not just a few tens of millions of years in age. Background note: Remember that a billion years is one thousand million years. Hence Holmes’s age of 1600 million years was equal to 1.6 billion years.
Presenter notes: As time went on, the use of radiometric dating became more and more widespread. Very soon, the precise age of different eons, eras, periods and epochs was figured out, but one question remained elusive: what was the exact age of the Earth? The big problem in answering this question was caused by the fact that the Earth has a dynamic crust that is constantly recycling itself. No rocks have survived intact from the earliest phase of planetary evolution. So far the oldest rock known on our planet is the Acasta Gniess which is found in Arctic Canada. Radiometric dating of isotopes trapped in zircon crystals in the rock have shown that this is an incredible 4030 million years old.
Presenter notes: Although the Acasta Gniess is the oldest known rock on our planet, even older fragments of earlier rocks have survived. In 2004, a single grain of a zircon mineral was dated from the Jack Hills of Australia. It was found to be an incredible 4404 million years old. This mineral formed in a rock that made up the Earth’s first crust, but was subsequently eroded away and an incorporated into a new rock. So although no actual crust has survived from this ancient time, tiny mineral flakes have been preserved.
Presenter notes: And yet, radiometric dating had identified even older materials on our planet: meteorites. Meteorites are debris left over from the formation of the solar system. One large meteorite was found in the Canyon Diablo region of Arizona in southwest USA. Studies show that it probably crashed to Earth about 20,000 years ago but that it had been wandered through space for much longer than that. Radiometric dating showed, in 1956, that the Canyon Diablo meteorite is around 4550 million years ago. Studies of many other meteorites have subsequently shown similar maximum ages. This tells us that the solar system – and the Earth in it – had formed by 4550 million years ago (4.55 billion years ago). The mineral flake found at Jack Hills Australia therefore tells us that the Earth had cooled down sufficiently to form a crust as early as 4404 million years ago, as little as 150 million years after the formation of the Earth.
Presenter notes: Radiometric dating has transformed our understanding of the age and history of our planet. Not only do we know the relative order in which events happened, but now we know precisely when they occurred on an absolute timescale. We know that our solar system – and the Earth in it – formed out of a nebula about 4550 million years ago. We know from well-dated fossils that the first life had appeared by 3800 million years ago and had evolved into complex cells by 2500 million years ago. We know than the first large animals arrived on the scene 800 million years and the famous dinosaurs had their day about between 65 and 180 million years ago. Finally we know that humans are a dramatic late arrival appearing only in the last blink of geological time, some 2 million year ago. However, although late arrivals, we have seen how human have transformed the Earth’s biosphere and climate to a unique degree and ushered in a new geological age – the Anthropocene.
Presenter notes: And that brings us to the end of this talk. Over the course of this session, we have discussed the age of the Earth and its geological timescale. We’ve seen how geologists have slowly chipped away at the Earth’s rocks for three centuries and in doing so uncovered the extraordinary geological history of our planet. We now know that Earth is not just a few thousand years old as Biblical scholars once believed, but more than 4500 million years old. This extraordinary discovery of geological time ranks as one of the most important scientific discoveries of all time. It has huge implications for our understanding of the origin of human beings and their place in the universe.