History of Life on Earth

Spontaneous Generation Spontaneous generation is the proposal that living organisms can arise from nonliving matter Medieval beliefs Microbes were thought to arise from broth Maggots were thought to arise from meat Mice were thought to arise from mixtures of sweaty shirts and wheat

Spontaneous generation is the proposal that living organisms can arise from nonliving matter

Medieval beliefs

Microbes were thought to arise from broth

Maggots were thought to arise from meat

Mice were thought to arise from mixtures of sweaty shirts and wheat

Spontaneous Generation Refuted The maggots-from-meat idea was disproved by Francesco Redi in 1668 He kept flies away from uncontaminated meat The broth-to-microorganism idea was disproved by Louis Pasteur and John Tyndall in the mid-1800s

The maggots-from-meat idea was disproved by Francesco Redi in 1668

He kept flies away from uncontaminated meat

The broth-to-microorganism idea was disproved by Louis Pasteur and John Tyndall in the mid-1800s

Spontaneous Generation Refuted Broth in flask is boiled to kill preexisting microogranisms As broth cools, condensing water collects, sealing the mouth of the flask If neck is later broken off, outside air can carry microorganisms into broth

Spontaneous Generation Refuted Did spontaneous generation occur on early Earth? Pasteur did not prove that spontaneous generation never happened He only showed that it does not happen under present-day conditions in an oxygen-rich atmosphere

Did spontaneous generation occur on early Earth?

Pasteur did not prove that spontaneous generation never happened

He only showed that it does not happen under present-day conditions in an oxygen-rich atmosphere

The First Living Things Alexander Oparin and John Haldane (1920s and 1930s) Noted that an oxygen-rich atmosphere would not have permitted the spontaneous formation of complex organic molecules Speculated that the atmosphere of early Earth contained little oxygen Proposed that prebiotic chemical evolution gave rise to life

Alexander Oparin and John Haldane (1920s and 1930s)

Noted that an oxygen-rich atmosphere would not have permitted the spontaneous formation of complex organic molecules

Speculated that the atmosphere of early Earth contained little oxygen

Proposed that prebiotic chemical evolution gave rise to life

The First Living Things Oparin and Haldane envisioned that prebiotic chemical evolution occurred in four stages Prebiotic synthesis and accumulation of small organic molecules Small organic molecules combined to form larger molecules Origin of self-replicating molecules Packaging of molecules within some kind of enclosing membrane

Oparin and Haldane envisioned that prebiotic chemical evolution occurred in four stages

Prebiotic synthesis and accumulation of small organic molecules

Small organic molecules combined to form larger molecules

Origin of self-replicating molecules

Packaging of molecules within some kind of enclosing membrane

Organic Molecules Stanley Miller and Harold Urey (1953) Noted that the atmosphere of early Earth probably contained methane, ammonia, hydrogen, and water vapor, but no oxygen

Stanley Miller and Harold Urey (1953)

Noted that the atmosphere of early Earth probably contained methane, ammonia, hydrogen, and water vapor, but no oxygen

Organic Molecules Miller and Urey (1953) Simulated early Earth’s atmosphere by mixing the above gases in a flask and adding an electrical discharge to simulate lightning Simple organic molecules appeared after a few days

Miller and Urey (1953)

Simulated early Earth’s atmosphere by mixing the above gases in a flask and adding an electrical discharge to simulate lightning

Simple organic molecules appeared after a few days

The Experiment of Miller & Urey Electric spark simulates lightning storm Organic molecules appear after only a few days Condenser Cool water flow Electric spark chamber CH 4 NH 3 H 2 Boiling chamber Gases of primeval atmosphere Purified water H 2 O H 2 O

Organic Molecules Similar experiments by Miller and others have produced amino acids, short proteins, nucleotides, and ATP Exact composition of “atmosphere” was unimportant Must contain carbon, hydrogen, and nitrogen, and exclude oxygen Type of energy source was unimportant Electrical discharge, UV light, and heat were equally effective

Similar experiments by Miller and others have produced amino acids, short proteins, nucleotides, and ATP

Exact composition of “atmosphere” was unimportant

Must contain carbon, hydrogen, and nitrogen, and exclude oxygen

Type of energy source was unimportant

Electrical discharge, UV light, and heat were equally effective

Organic Molecules Accumulate The lack of both life and oxygen gas on early Earth allowed large quantities of organic molecules to accumulate in areas protected from UV radiation (beneath rock ledges, in oceans) UV radiation bombarded early Earth’s surface because there was no ozone to block it UV radiation can break apart organic molecules Accumulated simple organic molecules combined to form complex organic molecules

The lack of both life and oxygen gas on early Earth allowed large quantities of organic molecules to accumulate in areas protected from UV radiation (beneath rock ledges, in oceans)

UV radiation bombarded early Earth’s surface because there was no ozone to block it

UV radiation can break apart organic molecules

Accumulated simple organic molecules combined to form complex organic molecules

RNA May have been the first self-reproducing molecule Thomas Cech and Sidney Altman (1980s) discovered an RNA molecule ( ribozyme ) that could catalyze a chemical reaction, a role that was thought to be performed only by protein enzymes

May have been the first self-reproducing molecule

Thomas Cech and Sidney Altman (1980s) discovered an RNA molecule ( ribozyme ) that could catalyze a chemical reaction, a role that was thought to be performed only by protein enzymes

RNA Since Cech and Altman’s initial discovery dozens of naturally-occurring ribozymes have been found that catalyze reactions including Cutting other RNA molecules Splicing together different RNA fragments Attaching amino acids to growing proteins

Since Cech and Altman’s initial discovery dozens of naturally-occurring ribozymes have been found that catalyze reactions including

Cutting other RNA molecules

Splicing together different RNA fragments

Attaching amino acids to growing proteins

RNA Since Cech and Altman’s initial discovery researchers have synthesized ribozymes that catalyze the replication of small RNA molecules Discovery of ribozymes led to hypothesis that RNA preceded the origin of DNA RNA served as The information-carrying genetic molecule The enzyme catalyst for its own replication

Since Cech and Altman’s initial discovery researchers have synthesized ribozymes that catalyze the replication of small RNA molecules

Discovery of ribozymes led to hypothesis that RNA preceded the origin of DNA

RNA served as

The information-carrying genetic molecule

The enzyme catalyst for its own replication

RNA Over time, DNA replaced RNA as the information-carrying genetic molecule and RNA took on its present role as an intermediary between DNA and protein

Over time, DNA replaced RNA as the information-carrying genetic molecule and RNA took on its present role as an intermediary between DNA and protein

Membrane-Like Vesicles Vesicles are small, hollow spheres formed from proteins or proteins complexed with other compounds Have been formed artificially by agitating water-containing proteins and lipids

Vesicles are small, hollow spheres formed from proteins or proteins complexed with other compounds

Have been formed artificially by agitating water-containing proteins and lipids

Membrane-Like Vesicles Vesicles resemble living cells Have a well-defined outer boundary that separates internal and external environments Depending on composition, membrane may be remarkably similar to that of a real cell Under certain conditions, may absorb material from the external solution, grow, and divide

Vesicles resemble living cells

Have a well-defined outer boundary that separates internal and external environments

Depending on composition, membrane may be remarkably similar to that of a real cell

Under certain conditions, may absorb material from the external solution, grow, and divide

Membrane-Like Vesicles Certain vesicles ( protocells ) may have been the precursors of living cells

Certain vesicles ( protocells ) may have been the precursors of living cells

Microspheres as Proto-Cells

When Did Life Arise on Earth? Earth formed about 4.5 billion years ago Life arose 3.9 to 3.5 billion years ago during the Precambrian era Oldest fossil organisms found to date are estimated to be about 3.5 billion years old

Earth formed about 4.5 billion years ago

Life arose 3.9 to 3.5 billion years ago during the Precambrian era

Oldest fossil organisms found to date are estimated to be about 3.5 billion years old

Earth's History Projected on a 24-hour Day Formation of Earth First Earth rocks 12 1 2 3 4 5 8 9 10 11 12 a.m. 6 7 1 2 3 4 5 7 8 9 10 11 MIDNIGHT NOON 6 p.m. First prokaryotes First atmospheric oxygen First eukaryotes First multicellular organisms First flowers First humans (11:59:40) First humans (11:59:40) Billions of years ago 4 3 2 1

Capturing the Sun’s Energy The first photosynthesizing organisms (ancestors of cyanobacteria) appeared about 3.5 billion years ago Photosynthesis requires sunlight, CO 2 , and hydrogen Earliest source of hydrogen believed to be hydrogen sulfide Eventually, water replaced hydrogen sulfide as the source of hydrogen and photosynthesis became water-based

The first photosynthesizing organisms (ancestors of cyanobacteria) appeared about 3.5 billion years ago

Photosynthesis requires sunlight, CO 2 , and hydrogen

Earliest source of hydrogen believed to be hydrogen sulfide

Eventually, water replaced hydrogen sulfide as the source of hydrogen and photosynthesis became water-based

Increased Oxygen in Atmosphere Water-based photosynthesis resulted in the release of oxygen gas as a by-product Initially, oxygen combined with iron in the Earth’s crust to form iron oxide Subsequently, oxygen began accumulating in the atmosphere Chemical analysis of rocks suggests that significant levels of atmospheric oxygen first appeared about 2.2 billion years ago

Water-based photosynthesis resulted in the release of oxygen gas as a by-product

Initially, oxygen combined with iron in the Earth’s crust to form iron oxide

Subsequently, oxygen began accumulating in the atmosphere

Chemical analysis of rocks suggests that significant levels of atmospheric oxygen first appeared about 2.2 billion years ago

Aerobic Metabolism The accumulation of oxygen in Earth’s atmosphere probably Exterminated many anaerobic organisms Provided the environmental pressure for the evolution of aerobic metabolism The evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms

The accumulation of oxygen in Earth’s atmosphere probably

Exterminated many anaerobic organisms

Provided the environmental pressure for the evolution of aerobic metabolism

The evolution of aerobic metabolism was significant because aerobic organisms can harvest more energy per food molecule than anaerobic organisms

Membrane-Enclosed Organelles The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis )

The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago

Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis )

Probable Origin of Mitochondria & Chloroplasts Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium Aerobic bacterium Descendents of engulfed bacterium evolve into mitochondria Photosynthetic bacterium Mitochondria-containing cell engulfs photosynthetic bacteria Descendents of photosynthetic bacteria evolve into chloroplasts

Evolution of Mitochondria Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest Predatory cell and bacterium gradually enter into a symbiotic relationship Descendants of engulfed bacterium evolve into mitochondria

Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest

Predatory cell and bacterium gradually enter into a symbiotic relationship

Descendants of engulfed bacterium evolve into mitochondria

Evolution of Chloroplasts Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium Predatory cell and bacterium gradually enter into a symbiotic relationship Descendants of engulfed bacterium evolve into chloroplasts

Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium

Predatory cell and bacterium gradually enter into a symbiotic relationship

Descendants of engulfed bacterium evolve into chloroplasts

Evidence for Endosymbionts Many biochemical features are shared by eukaryotic organelles and living bacteria Mitochondria, chloroplasts, and centrioles contain their own supply of DNA Living intermediates (modern cells that host bacterial endosymbionts) Pelomyxa palustris harbors aerobic bacteria Paramecium harbors photosynthetic bacteria

Many biochemical features are shared by eukaryotic organelles and living bacteria

Mitochondria, chloroplasts, and centrioles contain their own supply of DNA

Living intermediates (modern cells that host bacterial endosymbionts)

Pelomyxa palustris harbors aerobic bacteria

Paramecium harbors photosynthetic bacteria

Modern Intracellular Symbiosis Paramecium sp. Chlorella sp, a green alga

Cell Size Once predation evolved, increased cell size became an advantage Larger cells could more easily engulf smaller cells and they could move faster However, organisms larger than a millimeter in diameter can survive only in one of two ways Have a low metabolic rate Be multicellular

Once predation evolved, increased cell size became an advantage

Larger cells could more easily engulf smaller cells and they could move faster

However, organisms larger than a millimeter in diameter can survive only in one of two ways

Have a low metabolic rate

Be multicellular

Some Algae Become Multicellular The first multicellular organisms appeared in the seas about 1 billion years ago For plants, multicellularity allowed: Some protection from predation Specialization of cells (plants were able to anchor themselves in the brightly lit waters of the shoreline)

The first multicellular organisms appeared in the seas about 1 billion years ago

For plants, multicellularity allowed:

Some protection from predation

Specialization of cells (plants were able to anchor themselves in the brightly lit waters of the shoreline)

Some Algae Become Multicellular For animals, multicellularity allowed More efficient predation More effective escape from predators

For animals, multicellularity allowed

More efficient predation

More effective escape from predators

Animal Diversity Fossil traces of animal tracks and burrows have been found in 1 billion-year-old rocks Fossils of invertebrate animals (animals lacking backbones) have been collected from rocks 610 million to 544 million years old The oldest rock layers included fossils of ancestral sponges and jellyfish Subsequent rock layers revealed fossils of ancestral worms, mollusks, and arthropods

Fossil traces of animal tracks and burrows have been found in 1 billion-year-old rocks

Fossils of invertebrate animals (animals lacking backbones) have been collected from rocks 610 million to 544 million years old

The oldest rock layers included fossils of ancestral sponges and jellyfish

Subsequent rock layers revealed fossils of ancestral worms, mollusks, and arthropods

The Cambrian Explosion Most of the major phyla of animals had made their appearance by the Cambrian period of the Paleozoic era (544 million years ago) The Cambrian period was marked by an “explosion” in animal diversity (may have resulted from coevolution of predator and prey) Great diversity of ocean life arose during the Silurian period…

Most of the major phyla of animals had made their appearance by the Cambrian period of the Paleozoic era (544 million years ago)

The Cambrian period was marked by an “explosion” in animal diversity (may have resulted from coevolution of predator and prey)

Great diversity of ocean life arose during the Silurian period…

The Appearance of Fishes Fishes appeared in the fossil record about 530 million years ago They were the first vertebrates (animals with backbones) Over time, fish became the dominant predators in the oceans Faster than invertebrates Possessed more acute senses and larger brains than invertebrates

Fishes appeared in the fossil record about 530 million years ago

They were the first vertebrates (animals with backbones)

Over time, fish became the dominant predators in the oceans

Faster than invertebrates

Possessed more acute senses and larger brains than invertebrates

The Transition to Land The evolution of land plants The first land plants Mosses and ferns Continued water dependency Conifers - the invasion of dry habitats Flowering plants The dominant plant form today Pollination by insects

The evolution of land plants

The first land plants

Mosses and ferns

Continued water dependency

Conifers - the invasion of dry habitats

Flowering plants

The dominant plant form today

Pollination by insects

Evolution of Terrestrial Animals Arthropods Lobefin fish to amphibians Amphibians to reptiles The age of the dinosaurs Reptiles and maintenance of body temperature Birds Insulating feathers retain body heat Evolution of feathers for flight Mammals Insulating hair retains body heat Live births and mammary glands

Arthropods

Lobefin fish to amphibians

Amphibians to reptiles

The age of the dinosaurs

Reptiles and maintenance of body temperature

Birds

Insulating feathers retain body heat

Evolution of feathers for flight

Mammals

Insulating hair retains body heat

Live births and mammary glands

Multicellular Organisms Advantages of multicellularity Challenges of multicellularity The first multicellular organisms Plants - primitive marine algae Animals - marine invertebrates The transition to land

Advantages of multicellularity

Challenges of multicellularity

The first multicellular organisms

Plants - primitive marine algae

Animals - marine invertebrates

The transition to land

Diversity over Time 200 0 400 600 800 Millions of Years Ago Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Tertiary Number of Families Mass Extinctions 500 400 300 200 100 0 600

Plate Tectonics & Climate Change

Human Evolution Primate evolution Grasping hands - precision grip and power grip Binocular and color vision with overlapping fields of view Large brain - allows fairly complex social systems

Primate evolution

Grasping hands - precision grip and power grip

Binocular and color vision with overlapping fields of view

Large brain - allows fairly complex social systems

Hominid Evolution I The evolution of Dryopithecines - between 20 and 30 million years ago Australopithecines - the first true hominids Appeared 4 million years ago (fossils) Walked upright Large brains Homo habilis - 2 million years ago Larger body and brain Ability to make crude stone and bone tools

The evolution of Dryopithecines - between 20 and 30 million years ago

Australopithecines - the first true hominids

Appeared 4 million years ago (fossils)

Walked upright

Large brains

Homo habilis - 2 million years ago

Larger body and brain

Ability to make crude stone and bone tools

Hominid Evolution II Homo erectus - 1.8 million years ago Face of modern human More socially advanced Used fire & sophisticated stone tools Homo sapiens - 200,000 years ago Neanderthals evolved 100,000 years ago Similar to humans - muscular, fully erect, dexterous, large brains Developed ritualistic burial ceremonies Cro-Magnons evolved 90,000 years ago Direct descendants of modern humans Were artistic and made precision tools

Homo erectus - 1.8 million years ago

Face of modern human

More socially advanced

Used fire & sophisticated stone tools

Homo sapiens - 200,000 years ago

Neanderthals evolved 100,000 years ago

Similar to humans - muscular, fully erect, dexterous, large brains

Developed ritualistic burial ceremonies

Cro-Magnons evolved 90,000 years ago

Direct descendants of modern humans

Were artistic and made precision tools

Possible Human Line of Descent Millions of Years Ago Ardipithecus ramidus A. boisei A. africanus Australopithecus afarensis A. robustus Homo habilis H. erectus H. heidel- bergensis H. neander- thalensis Homo ergaster H. sapiens 5 4 3 2 1 0

The “Out of Africa” Theory H. erectus spread began ~1.8 mya H. sapiens spread began ~100 kya

The “Multiregional” Hypothesis Regional pops of H. erectus may have evolved into H. sapiens while intermingling.

The End