The Origin and Evolutionary The Origin and Evolutionary History of LifeHistory of Life

Chapter 21 Chapter 21

Learning Objective 1Learning Objective 1

• What conditions do geologists think What conditions do geologists think existed on early Earth?existed on early Earth?

Early EarthEarly Earth

The Origin of LifeThe Origin of Life

• Biologists generally agreeBiologists generally agree• life originated from nonliving matterlife originated from nonliving matter• by by chemical evolutionchemical evolution

• Origin of life is difficult to test experimentallyOrigin of life is difficult to test experimentally• testable hypotheses about chemical evolutiontestable hypotheses about chemical evolution

KEY CONCEPTSKEY CONCEPTS

• Although there is no direct fossil evidence Although there is no direct fossil evidence of the origin of life, biochemical of the origin of life, biochemical experiments have demonstrated how experiments have demonstrated how complex organic molecules, found in all complex organic molecules, found in all living organisms, may have formedliving organisms, may have formed

4 Requirements for 4 Requirements for Chemical EvolutionChemical Evolution

1. Absence of oxygen1. Absence of oxygen• oxygen would oxidize abiotically produced oxygen would oxidize abiotically produced

organic molecules organic molecules

2. Energy 2. Energy • to form organic molecules to form organic molecules

4 Requirements for 4 Requirements for Chemical EvolutionChemical Evolution

3. Chemical building blocks3. Chemical building blocks• water, minerals, gases in atmospherewater, minerals, gases in atmosphere• to form organic molecules to form organic molecules

4. Sufficient time4. Sufficient time• for molecules to accumulate and reactfor molecules to accumulate and react

Learn more about conditions on Learn more about conditions on early Earth by clicking on the early Earth by clicking on the

figure in ThomsonNOW.figure in ThomsonNOW.

Learning Objective 2Learning Objective 2

• Contrast the Contrast the prebiotic soupprebiotic soup hypothesis and hypothesis and the the iron–sulfur worldiron–sulfur world hypothesishypothesis

Chemical EvolutionChemical Evolution

• Prebiotic soup hypothesisPrebiotic soup hypothesis• organic molecules formed near Earth’s organic molecules formed near Earth’s

surface in “sea of organic soup” or on rock or surface in “sea of organic soup” or on rock or clay surfaces clay surfaces

• Iron–sulfur world hypothesisIron–sulfur world hypothesis• organic molecules produced at organic molecules produced at hydrothermal hydrothermal

ventsvents in deep ocean floor in deep ocean floor

Miller and Urey’s Miller and Urey’s ExperimentExperiment

Fig. 21-2, p. 449

Electrodes

NH3

CH4

To vacuum

H2O H2

Spark chamber

Condenser

Boiling chamber

Organic molecules collect in the trapHeat source

Insert “Miller's reaction Insert “Miller's reaction chamber experiment”chamber experiment”

Miller_Urey.swfMiller_Urey.swf

See the Miller–Urey experiment See the Miller–Urey experiment unfold by clicking on the figure unfold by clicking on the figure

in ThomsonNOW.in ThomsonNOW.

Learning Objective 3Learning Objective 3

• What major steps are hypothesized to What major steps are hypothesized to have occurred in the have occurred in the origin of cellsorigin of cells??

The Origin of CellsThe Origin of Cells

• MacromoleculesMacromolecules• assembled from assembled from small organic moleculessmall organic molecules

• Protobionts Protobionts ((macromolecular assemblages)macromolecular assemblages)• formed from formed from macromoleculesmacromolecules

• CellsCells• arose from arose from protobiontsprotobionts

MicrospheresMicrospheres

RNA WorldRNA World ModelModel

• RNARNA• first informational molecule to evolvefirst informational molecule to evolve• progression toward self-reproducing cellprogression toward self-reproducing cell

• Natural selection at molecular levelNatural selection at molecular level• resulted in information sequenceresulted in information sequence• DNA → RNA → proteinDNA → RNA → protein

RNA MoleculesRNA Molecules

Fig. 21-4, p. 451

Large pool of RNA molecules

Selection for ability to catalyze a chemical reaction

Molecules with some ability to catalyze the reaction

Amplification and mutation to create large pool of similar RNA molecules

Repeat the selection–amplification–mutation process

Molecules with best ability to catalyze the reaction

Stepped Art

Fig. 21-4, p. 451

Large pool of RNA molecules

Selection for ability to catalyze a chemical reaction

Molecules with some ability to catalyze the reaction

Amplification and mutation to create large pool of similar RNA molecules

Repeat the selection–amplification–mutation process

Molecules with best ability to catalyze the reaction

Learning Objective 4Learning Objective 4

• How did the evolution of How did the evolution of photosynthetic photosynthetic autotrophsautotrophs affected both the atmosphere affected both the atmosphere and other organisms?and other organisms?

The First CellsThe First Cells

• Prokaryotic Prokaryotic heterotrophsheterotrophs • obtained organic molecules from environment obtained organic molecules from environment • probably probably anaerobesanaerobes

• Autotrophs Autotrophs • evolved laterevolved later• produced organic molecules by photosynthesisproduced organic molecules by photosynthesis

PhotosynthesisPhotosynthesis

• Generated oxygen in atmosphereGenerated oxygen in atmosphere• changed early lifechanged early life• permitted evolution of permitted evolution of aerobesaerobes

• AerobesAerobes• use oxygen for efficient cellular respirationuse oxygen for efficient cellular respiration

OzoneOzone

Fig. 21-6, p. 453

Su

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ltra

vio

let

rays

3(O2)

Up

per

atm

os

ph

ere

2(O3)

Lo

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mo

sph

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Learning Objective 5Learning Objective 5

• What is the hypothesis of What is the hypothesis of serial serial endosymbiosisendosymbiosis??

Serial EndosymbiosisSerial Endosymbiosis

• Eukaryotic cells arose from prokaryotic Eukaryotic cells arose from prokaryotic cellscells

• Certain eukaryotic organelles Certain eukaryotic organelles (mitochondria, chloroplasts) evolved from (mitochondria, chloroplasts) evolved from prokaryotic endosymbiontsprokaryotic endosymbionts• incorporated within larger prokaryotic hostsincorporated within larger prokaryotic hosts

Serial EndosymbiosisSerial Endosymbiosis

Fig. 21-7, p. 454

ORIGINAL PROKARYOTIC HOST CELL

DNA

Multiple invaginations of the plasma membrane

Aerobic bacteria

Endoplasmic reticulum and nuclear envelope form from the plasma membrane invaginations (not part of serial endosymbiosis)

Aerobic bacteria become mitochondria

Photosynthetic bacteria...

... become chloroplasts

EUKARYOTIC CELLS: PLANTS, SOME PROTISTS

EUKARYOTIC CELLS: ANIMALS, FUNGI, SOME PROTISTS

Insert “The endosymbiont Insert “The endosymbiont theory”theory”

endosymbiont_theory_m.swfendosymbiont_theory_m.swf

Learn more about Learn more about endosymbiosis by clicking on endosymbiosis by clicking on the figure in ThomsonNOW.the figure in ThomsonNOW.

KEY CONCEPTSKEY CONCEPTS

• Photosynthesis, aerobic respiration, and Photosynthesis, aerobic respiration, and eukaryotic cell structure represent several eukaryotic cell structure represent several major advances that occurred during the major advances that occurred during the early history of lifeearly history of life

Learning Objective 6Learning Objective 6

• What are the distinguishing organisms and What are the distinguishing organisms and major biological events of the major biological events of the Ediacaran Ediacaran periodperiod and the and the Paleozoic, Mesozoic, Paleozoic, Mesozoic, andand Cenozoic erasCenozoic eras

Proterozoic EonProterozoic Eon

• 2500 mya to 542 mya2500 mya to 542 mya• life consisted of life consisted of prokaryotesprokaryotes

• About 2.2 byaAbout 2.2 bya• first first eukaryoticeukaryotic cells appeared cells appeared

Ediacaran PeriodEdiacaran Period

• Ediacaran periodEdiacaran period• 600 mya to 542 mya600 mya to 542 mya• last period of Proterozoic eonlast period of Proterozoic eon

• Ediacaran fossilsEdiacaran fossils• oldest known fossils of multicellular animalsoldest known fossils of multicellular animals

• Ediacaran faunaEdiacaran fauna• small, soft-bodied invertebratessmall, soft-bodied invertebrates

An Ediacaran SeaAn Ediacaran Sea

The Paleozoic Era (1)The Paleozoic Era (1)

• Began about 542 mya Began about 542 mya • lasted about 291 million yearslasted about 291 million years

• Many plants and animals appearedMany plants and animals appeared• all major plants (except flowering plants)all major plants (except flowering plants)• all animal phylaall animal phyla• reptilesreptiles• fishes and amphibians flourishedfishes and amphibians flourished

Cambrian RadiationCambrian Radiation

Fig. 21-9a, p. 457

Fig. 21-9b, p. 457

Fig. 21-9c, p. 457

Devonian PeriodDevonian Period

Fig. 21-10, p. 458

(b) Pterapsis

(c) Jamoytius

(a) Thelodus

Carboniferous PeriodCarboniferous Period

The Paleozoic Era (2)The Paleozoic Era (2)

• Greatest mass extinction of all timeGreatest mass extinction of all time• at end of at end of Paleozoic eraPaleozoic era (251 mya) (251 mya)• > 90% of marine species extinct> 90% of marine species extinct• 70% of land-dwelling vertebrate genera 70% of land-dwelling vertebrate genera • many plant speciesmany plant species

The Mesozoic EraThe Mesozoic Era

• Began about 251 myaBegan about 251 mya• lasted about 185 million years lasted about 185 million years

• Dinosaurs dominatedDinosaurs dominated• reptiles diversified reptiles diversified • insects flourished insects flourished • flowering plants appearedflowering plants appeared• birds appearedbirds appeared• early mammals appearedearly mammals appeared

Triassic PeriodTriassic Period

Cretaceous PeriodCretaceous Period

Cretaceous PeriodCretaceous Period

• 66 mya66 mya• end of end of Cretaceous periodCretaceous period• many species abruptly became extinctmany species abruptly became extinct

• Collision of extraterrestrial body with EarthCollision of extraterrestrial body with Earth• may have caused dramatic climate changesmay have caused dramatic climate changes• resulted in mass extinctionresulted in mass extinction

Cenozoic EraCenozoic Era

• From 66 mya to presentFrom 66 mya to present• flowering plants, birds, insects, mammals flowering plants, birds, insects, mammals

diversified greatlydiversified greatly

• Late MioceneLate Miocene and and Early Pliocene epochsEarly Pliocene epochs• human ancestors appeared in Africa human ancestors appeared in Africa

The Fossil RecordThe Fossil Record

Fig. 21-15a, p. 461

Saurischians

Ilium Hip socket

Pubis

Ischium

Coelophysis

The saurischian pelvis

Fig. 21-15b, p. 461

OrnithischiansIlium

Hip socket

PubisIschium

Stegosaurus

The ornithischian pelvis

KEY CONCEPTSKEY CONCEPTS

• The fossil record tells us much of what we The fossil record tells us much of what we know about the history of life, such as know about the history of life, such as what kinds of organisms existed and what kinds of organisms existed and where and when they livedwhere and when they lived

Fossil TrilobitesFossil Trilobites

KEY CONCEPTSKEY CONCEPTS

• Certain organisms appear in the fossil Certain organisms appear in the fossil record, then disappear and are replaced record, then disappear and are replaced by othersby others

StromatolitesStromatolites

KEY CONCEPTSKEY CONCEPTS

• Scientists identify and demonstrate Scientists identify and demonstrate relationships among fossils in rock layers relationships among fossils in rock layers from different periods of geologic timefrom different periods of geologic time