Ch20 lecture history of life 1

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 20

The Origin and The Origin and Evolutionary HistoryEvolutionary History

of Lifeof Life

Biology, Seventh Edition CHAPTER 20 The Origin and Evolutionary History of Life

• Conditions on early Earth• Age of Earth is ~4.6 billion years

• Atmosphere had little free O2

–Included CO2, H2O, CO, H2, N2

–Maybe also NH3, H2S, CH4

• Requirements for chemical evolution to produce life• Absence of oxygen

• Energy

• Chemical building blocks

• Sufficient time

• Prebiotic soup hypothesis• Molecules formed near the

Earth’s surface

• Sugars, nucleotides, amino acids formed spontaneously

Miller-Urey experiment

• Iron-sulfur world hypothesis• Organic molecules formed at

hydrothermal vents on the ocean floor

• Laboratory simulations show catalyst effects of iron and nickel sulfides

• Origin of cells• Spontaneous assembly of small

organic molecules into macromolecules

• Protobionts similar to cells–Binary fission

–Homeostasis

–Catalytic activity

Microspheres – a type of protobiont

• Microspheres• Formed from water and

polypeptides

• Electric gradient on surface

• Selective permeability

• RNA world• Self-replicating RNA molecules

• Function as both enzyme and substrate for replication–Ribozyme is enzymatic RNA

• First step in evolution of theDNA / RNA / protein system

• Directed evolution• Large pool of RNA molecules

with different sequences• Selected for ability to catalyze a

reaction• Amplify / mutate / repeat

Directed evolution

• In the RNA world, ribozymes catalyzed protein synthesis

• DNA formed from double strands of RNA

• DNA more stable than RNA

• The first cells• Heterotrophs that feed on organic

molecules• Anaerobic fermentation process

to obtain energy

• Autotrophs• Selected after organic molecule

food stock became scarce• Photosynthetic production of

organic molecules• Cyanobacteria split water

molecules and released oxygen

• Aerobes• More efficient energy production

using oxygen respiration• Significant oxygen in the

atmosphere by 2 bya

• Formation of the ozone layer• Ultraviolet radiation forms O3 from

O2 in the upper atmosphere

• Prevents UV from reaching Earth• Decreased mutagenesis• Enabled organisms to live in

surface waters and on land

Ozone formation

• Eukaryotes arose from prokaryotes• Endosymbiont theory

–Mitochondria and chloroplasts derived from prokaryotes

–Ingested but not digested

–Reproduced along with host cell

Endosymbiont theory

• Geological eras• Paleozoic

–543 mya - 251 mya

• Mesozoic–251 mya - 65 mya

• Cenozoic–65 mya - present

Using a clock to represent biological time

• Precambrian time• Before 543 mya• Bacteria• Protists• Fungi• Simple multicellular animals

• Cambrian explosion• All animal phyla established• Many new body plans• Bizarre, extinct phyla

• Ordovician period• Shallow seas covered land• Cephalopods• Coral reefs• Jawless fishes

• Silurian period• Jawed fishes• Terrestrial plants• Air-breathing animals

• Devonian period• Bony fishes• Amphibians• Wingless insects• All major plant groups except for

flowering plants established

• Carboniferous period• Swamp forests• Reptiles• Winged insects

Carboniferous forest

• Permian period• Therapsids

–Reptilian ancestors of mammals

• Seed plants dominant• Ended the Paleozoic with the

greatest mass extinction–90% of marine species–70% of land vertebrates

Mesozoic Era

• Triassic period• Thecodonts

–Ancestors of dinosaurs and birds

• Pleiosaurs and ichthyosaurs

• Pterodonts• First mammals

–Small insectivores

• Jurassic and Cretaceous periods• Saurischians

–Ancestors of lizards

• Ornithischians–Ancestors of birds

• Ended with mass extinction caused by a meteorite impact

Saurischians

Ornithischians

Cenozoic Era

• Tertiary period• Diversification of flowering plants,

birds, insects, mammals

• Quaternary period• Genus Homo

• Large mammals

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