Diversity of Life

• Speciation – process by which new species arrive.

• Macroevolution – evolution on a grand scale

• Adaptive radiation - evolution of many diversely adapted species from a common ancestor

Chapter 26: Early Earth and the Origin of Life

• Introduction to the History of Life• The Origin of Life

•Organic (Chemical) Evolution

• Major Lineages of Life

How did life begin on earth?

Introduction to the History of Life

• Conditions on early Earth• Four Stage Hypothesis of Origin• RNA, the first genetic material• Natural selection’s role – directed

evolution

• Four Stage Hypothesis of Origin

1. Abiotic synthesis of building blocks

2. Production of organic polymers3. Origin of self-replicating molecules

(making inheritance possible)4. Protobionts are packaged with

material that makes internal chemistry different from surroundings

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

•Lack of oxygen meant that the environment would have “reducing” nature

What is needed for life to evolve?

• Requirements for chemical evolution to produce life•Absence of oxygen•Energy•Chemical building blocks•Sufficient time

Abiotic synthesis of building blocks: a testable hypothesis

• 1920s – A.I. Oparin and J.B.S. Haldane

• 1953 – Stanley Miller and Harold Urey test the Oparin-Haldane hypothesis

Miller-Urey experiment

Production of organic polymers

•Other hypotheses:• “hot rocks” – organic molecules are

concentrated as water evaporates from geothermal activity

• Clay – clay contains charged particles which retains organics when runoff is collected

• Deep sea vents produce many inorganic catalysts that could aid in the making of polymers

The 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

Protobionts - similar to cells

• Separate internal environment from external surroundings by a biological membrane• As protobionts became more similar to cells they

would have evolved the following:• Binary fission• Homeostasis• Catalytic activity

Figure 26.12 Laboratory versions of protobionts

Microspheres – a type of protobiont

Two types of Protobionts

• Microspheres•Formed from water and polypeptides•Electric gradient on surface•Selective permeability

• Liposomes•Lipids organized into a molecular bilayer•Selective permeability•Behave dynamically – grow, split, etc.

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

Living and Fossilized Stromatolites

The First Autotrophs

• Organic molecule food stock became scarce

• Photosynthetic production of organic molecules

• Cyanobacteria evolved later and could split water molecules which released oxygen

The First Aerobes

• More efficient energy production using oxygen respiration

• Significant oxygen in the atmosphere-2 bya

Formation of the Ozone Layer

• Ultraviolet radiation forms O3 from O2 in the upper atmosphere

• Prevents UV from reaching Earth• 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

Major Lineages of Life

• Linnaeus’ two-kingdom system•Plant (non-moving) and Animal (moving)

• Robert Whittaker’s five-kingdom system•Plantae, Animalia, Fungi, Protista, Monera

• Carl Woese’s three-domain system•Eukarya, Archaea, Bacteria

Figure 26.16 Our changing view of biological diversity

Key Periods in the History of Earth

Glaciations; mammals increased; humans

Mammals diversified; grasses

Aquatic reptiles diversified; flowering plants; mass extinction

Dinosaurs diversified; birds

Dinosaurs; small mammals; cone-bearing plants

Reptiles diversified; seed plants; mass extinction

Reptiles; winged insects diversified; coal swamps

Fishes diversified; land vertebrates (primitive amphibians)

Land plants; land animals (arthropods)

Aquatic arthropods; mollusks; vertebrates (jawless fishes)

Marine invertebrates diversified; most animal phyla evolvedAnaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life

Cenozoic

Mesozoic

Paleozoic

PrecambrianTime

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

1.8–present

65–1.8

145–65

208–145

245–208

290–245

363–290

410–363

440–410

505–440

544–505

650–544

Key EventsEra Period Time(millions of years ago)