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Op ch12 lecture_earth3, geological time

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T he geologic time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used bygeologists, paleontologists, and other earth scientists to describe the timing ...

T he geologic time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used bygeologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history. The table of geologic time spans presented here agrees with the dates and nomenclature set forth by theInternational Commission on Stratigraphy standard color codes of the International Commission on Stratigraphy.
Evidence from radiometric dating indicates that the Earth is about 4.54 billion years old. The geology or deep time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the GTS are usually delimited by changes in the composition of strata which correspond to them, indicating major geological or paleontological events, such as mass extinctions.
Geological time, Understanding of Earth history,
Solar technologies , Mineral resources , Igneous rock .definition of a mineral , Alfred Wegener Earth's lithosphere,plate tectonics, Abraham Ortelius , The continents drift, the Earths interior, drrobisawesome, ESE 11, Bronx Community college

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Op ch12 lecture_earth3, geological time Op ch12 lecture_earth3, geological time Presentation Transcript

  • Chapter 12 Deep Time: How Old Is Old? LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Deep Time: How Old Is Old? Prepared by Ronald Parker Earlham College Department of Geosciences Richmond, Indiana
  • Geologic Time Discovering the magnitude of the Earth’s past was a momentous discovery in the history of humanity.  This discovery forever altered our perception of ourselves within nature and the Universe.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? View slide
  • Geologic Time  Understanding time permits assigning an age to… Rocks.  Fossils.  Geologic structures.  Landscapes.  Tectonic events.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old? View slide
  • Geologic Time Deep time – The immense span of geologic time.  It is so vast that it is difficult for people to grasp.   We think of time in terms of our lives… The lives of our parents and grandparents. The lives of our children or grandchildren.  Human history is tiny compared to geologic time. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  Prior to the late 17th century, geologic time was thought to be the same as historical time.  Archbishop James Ussher of Armagh, Ireland, 1654. He added up generations from the Old Testament. He determined that Earth formed on October 23, 4004 BCE. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  Scientists began to find clues to an ancient Earth.  Nicolaus Steno (1638–1686) – Danish physician. Observed marine fossils high in the Apennines. Deduced that these were ancient animals in loose sediment. Lithification and uplift suggested long periods of time. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  James Hutton (1726-1797) – Scottish physician. Called “the Father of Modern Geology.”  First to articulate the “Principle of Uniformitarianism.”  Of the abyss of time, Hutton wrote: “we find no vestige of a beginning; no prospect of an end.”  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  James Hutton’s Principle of Uniformitarianism.  “The present is the key to the past.” Processes seen today are the same as those of the past. Ancient mudcracks formed as mudcracks do today. Geologic change is slow; large changes require large times. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  There are two ways of dating geological materials.  Relative ages – Based upon order of formation. Qualitative method developed 100s of years ago. Permit determination of older vs. younger relationships.  Numerical ages – Actual number of years since an event. Quantitative method developed recently. Age is given a number. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative vs. Absolute Relative ages assign order to events.  Numerical ages assign exact dates to events.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Logical tools are useful for defining relative age. Principle of uniformitarianism.  Principle of superposition.  Principle of original horizontality.  Principle of original continuity.  Principle of cross-cutting relationships.  Principle of inclusions.  Principle of baked contacts.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  Uniformitarianism – The present is key to the past. Physical processes that we observe today operated in the same way in the geological past.  Modern processes help us understand ancient events.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Defining Relative Age  Superposition.  In an undeformed sequence of layered rocks… Each bed is older than the one above and… Younger than the one below.  Younger strata are on top; older strata below. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Horizontality and continuity. Strata often form laterally extensive horizontal sheets.  Subsequent erosion dissects once-continuous layers.  Flat-lying rock layers are unlikely to have been disturbed.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Cross-cutting relations. Younger features truncate (cut across) older features.  Faults, dikes, erosion, etc., must be younger than the material that is faulted, intruded, or eroded.  A volcano cannot intrude rocks that aren’t there yet.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Inclusions – A rock fragment within another. Igneous xenoliths – Country rock that fell into magma.  Weathering rubble – Debris from pre-existing rocks.   The inclusion is older than the material enclosing it. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Baked contacts. Thermal metamorphism occurs when country rock is invaded by a plutonic igneous intrusion.  The baked rock must have been there first (it is older).  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Relative Age  Determining relative ages empowers geologists to easily unravel complicated geologic histories. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Deposition of horizontal strata below sea level in order 1, 2, 3, 4, 5, 6, 7, and 8 (oldest to youngest). Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Igneous intrusion of a sill. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Tectonic compression and folding.   Beds had to be present to be folded. Uplift above sea level and erosion. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Intrusion of a granitic igneous pluton. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Extensional normal faulting.  Faulting cross-cuts the older granitic pluton. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Intrusion of a dike.  Dike cross-cuts the normal fault. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History  Erosion to present landscape configuration.  Erosion removed the volcano and cross-cuts the dike. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic History Relative ages help to unravel a complicated history.  Simple rules permit one to decipher this diagram.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Fossil Succession Fossil remnants, or traces of once living organisms, are often preserved in sedimentary rocks.  Fossil are useful for relative age determination.  Several types of fossils will occur as an assemblage.  Fossils are time markers.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Fossil Succession Species evolve, exist for a time, and then go extinct.  First appearance, range, and extinction dates rocks.  Fossils succeed one another in a known order.  A time period is recognized by its fossil content.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Fossil Succession  Fossil range – First and last appearance. Each fossil has a unique range.  Overlapping ranges provide distinctive time markers.   Permit correlation of strata. Locally.  Regionally.  Globally.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Unconformities  An unconformity is a time gap in the rock record. Nondeposition.  Erosion.   There are three types of unconformity. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Unconformities  Three unconformity types:  Disconformity – Parallel strata bracketing nondeposition. Due to an interruption in sedimentation. May be difficult to recognize. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Disconformities
  • Unconformities  Three unconformity types:  Nonconformity – Metamorphic or igneous rocks overlain by sedimentary strata. Crystalline ig/met rocks were exposed by erosion. Sediment was deposited on this eroded surface. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Nonconformity
  • Unconformities  Three unconformity types:  Angular unconformity – Represents a huge gulf in time. Horizontal marine sediments deformed by orogenesis. High mountains are eroded away to below sea level. Sediments deposited horizontally on the erosion surface. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Angular Unconformity  James Hutton was the 1st to realize the enormous time-significance of angular unconformities. Mountains created.  Mountains completely erased.  New sediment deposition.   Incomprehensible time. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Angular Unconformity  “Hutton’s Unconformity” on Siccar Point, Scotland, is a common destination for geologists. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Unconformities Earth history is recorded in strata.  Missing strata = missing history.  The Grand Canyon.  Thick layers of strata.  Numerous gaps.  A partial record of geological history.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Stratigraphic Correlation  Stratigraphic columns depict strata in a region. Drawn to scale to accurately portray relative thicknesses.  Rock types are depicted by graphical fill patterns.  Divided into formations.  Mapable rock units.  Formations are separated by contacts. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Stratigraphic Correlation  In 1793, William “Strata” Smith was the first to note that strata could be matched across distances. Similar rock types in a similar order.  Rock layers contained the same distinctive fossils.   After years of work, he made the 1st geologic map. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Stratigraphic Correlation  Lithologic correlation is based on rock type. Sequence – The relative order in which the rocks occur.  Limited to correlation between nearby regions.   Fossil correlation – Based on fossils within rocks.  Applicable to much broader areas. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Stratigraphic Correlation  National parks of Arizona and Utah. Formations can be traced long distances.  Overlap is seen in the sequences of rock types.  Overlapping rock columns are used to build a composite.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Correlation among rock strata in 3 national parks.
  • The Geologic Column  A composite stratigraphic column exists. Constructed from incomplete sections across the globe.  It brackets almost the entirety of Earth history.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time The composite column is divided into time blocks.  This is the geologic time scale, Earth’s “calendar.”   The structure of the geologic time scale. Eons – The largest subdivision of time (100s to 1000s Ma). Eras – Subdivisions of an eon (65 to 100s Ma). Periods – Subdivisions of an era (2 to 70 Ma). Epochs – Subdivisions of a period (0.011 to 22 Ma). Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time  Time scale subdivisions are variously named. The nature of life (“zoic” means life); i.e., Proterozoic.  A characteristic of the time period; i.e., Carboniferous.  A specific locality; i.e., Devonian.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • The Geologic Time Scale Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time and Life      Life first appears on Earth ~ 3.8 Ga. Early life consisted of anaerobic single-celled organisms. Oxygen from cyanobacteria built up by 2 Ga. ~ 700 Ma, multicellular life evolved. ~ 542 Ma marks the 1st appearance of hard shells.   Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Shells increased fossil preservation. Life diversified rapidly – the “Cambrian Explosion.” Chapter 12: Deep Time: How Old Is Old?
  • The Geologic Time Scale  Names of the eons.  Phanerozoic – “Visible life” (542 Ma to the present). Started 542 Ma at the Precambrian – Cambrian boundary. Marks the 1st appearance of hard shells. Life diversified rapidly afterward.  Proterozoic – “Before life” (2.5 to 0.542 Ga). Development of tectonic plates like those of today. Buildup of atmospheric O2; multicellular life appears.  Archean – “Ancient” (3.8 to 2.5 Ga). Birth of continents. Appearance of the earliest life forms.  Hadean – “Hell” (4.6 to 3.8 Ga). Internal differentiation. Formation of the oceans and secondary atmosphere. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • The Geologic Time Scale  Names of the eras.  Cenozoic – “Recent life.” 65.5 Ma to present. The “Age of Mammals.”  Mesozoic – “Middle life.” 251 to 65.5 Ma. The “Age of Dinosaurs.”  Paleozoic – “Ancient life.” 542 to 251 Ma. Life diversified rapidly. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Numerical Age The relative age of geologic events is established.  Based on radioactive decay of atoms in minerals.  Radioactive decay proceeds at a known, fixed rate.  Radioactive elements act as internal clocks.   Numerical dating is also called geochronology. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Radioactive Decay Isotopes – Atoms with the same # of protons, different # of neutrons.  Isotopes have similar but different mass numbers.  Stable – Isotopes that never change (i.e., 13C).  Radioactive – Isotopes that spontaneously decay.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Radioactive Decay  Radioactive decay progresses along a decay chain. Decay creates new unstable elements that also decay.  Decay proceeds to a stable element endpoint.  Parent isotope – The isotope that undergoes decay.  Daughter isotope – The product of this decay.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Radioactive Decay  Half-life (t½) – Time for ½ unstable nuclei to decay.   After one t½ half of the original parent remains.   t½ is a characteristic of each isotope. After three t½ an eighth of the original parent remains. As the parent disappears, the daughter “grows in”. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Radiometric Dating  The age of a mineral can be determined by… Measuring the ratio of parent to daughter isotopes.  Calculating the amount of time by using the known t½.  Must pick the right mineral and the right isotope.  Geochronology requires analytical precision.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • What Is a Radiometric Date?  Radiometric dates give the time a mineral began to preserve all atoms of parent and daughter isotopes. Requires cooling below a “blocking temperature.”  If rock is reheated, the radiometric clock can be reset.  Ig / Met rocks are best for geochronologic work.  Sedimentary rocks cannot be directly dated.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Other Numerical Ages  Numerical ages are possible without isotopes. Growth rings – Annual layers from trees or shells.  Rhythmic layering – Annual layers in sediments or ice.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Other Numerical Ages  Magnetostratigraphy – Magnetic signatures in strata are compared to the global reference column. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Other Numerical Ages  Fission-track analysis – Measuring decay paths. Radioactive decay particles scar crystals.  The number of scars is proportional to age.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Dating the Geologic Column Geochronology less useful for sediment deposits.  It can, however, constrain these deposits.  Sediments can be bracketed by absolute dates.  Yields age ranges that improve as data accumulates.  Defines major boundaries in the geologic column.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • The Age of the Earth  Before radioactivity-based dating methods… 20 Ma – From Earth cooling.  90 Ma –Ocean salinization.  Assumed oceans were initially freshwater. Measured the mass of dissolved material in rivers.  Uniformitarianism and evolution indicated an Earth older than ~100 Ma. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • The Age of the Earth The oldest rocks on Earth’s surface date to 3.96 Ga.  Zircons in ancient sandstones date to 4.1-4.2 Ga.  Age of Earth is 4.57 Ga based on correlation with…  Meteorites.  Moon rocks.  Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time The immensity of time is beyond comprehension.  Metaphors illustrate the scale of time.  The age of Earth (4.6 Ga) can be compared to pennies.  Lined up, 4.6 billion pennies would be 87,400 km long.  More than twice around Earth. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • Geologic Time Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?
  • This concludes the Chapter 12 Deep Time: How Old Is Old? LECTURE OUTLINE earth Portrait of a Planet Third Edition ©2008 W. W. Norton & Company, Inc. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 12: Deep Time: How Old Is Old?