Origin of Life (overview)1. Chemical evolution2. Replicators- RNA or DNA?3. Individuality: Protocells --> cells4. Prokaryotes: Earliest true cells (~3.5 bya)5. Endomembrane system: Increase in

cellular complexity6. Endosymbiosis: Further increase in

eukaryote complexity and expansion of biochemistry

7. Multicellularity: Cooperative grouping of differentiated, clonally related cells

Logic of Origin of Life

1. Diverse environment2. Lots of Time --> perhaps hundreds of

millions of years3. Non-oxidizing atmosphere --> without

lots of O2 around, organic molecules are much more stable

4. Organic molecule stability without O2 allowed life to evolve slowly from nonliving material

5. Organic Molecules

Logic of Origin of Life1. Energy - volcanoes, deep-sea vents,

lightning, sun light, chemicals from space

2. natural selection:

• Stuff that is durable and easily made tends to accumulate

• Chemicals that are stable, and can duplicate themselves, naturally increase in abundance

3. Little Early Competition

Oparin’s hypothesisEarly Earth needed

•Water vapor

•Carbon dioxide

•Methane

•Nitrogen

•ammonia

Miller & Urey Experiment (1953)

Miller and Urey

devised the experiment

Extraterrestrial Energy Sources

Terrestrial Energy Sources

oceanic geothermal

vents (underwater geysers and hot springs)

Laboratory Protobionts

Shown is some degree of abiotic individuality

Relative Vs Absolute Dating

Relative dating:• Geological time scales• Relative position in

rock strata• Index fossils- trilobites Absolute dating:• Actual “clock”• E.g., radioactive decay

Radiocarbon Dating

The Carbon 14 Dating Process

1 atom of C14 for every 1013 C12 atoms in the atmosphere

Once an organism dies, the C14 is trapped and decays. Half-life is about 5800 years

1. Bacteria and Archea diverge- 2-3 bya2. Photosynthetic bacteria produce

oxygen- 2.5 bya3. Eukaryotes emerge- 2 bya4. Plants emerged from green algae ~700

mya5. Fungi and animals emerge from uni-

cells ~ 700 mya 6. First terrestrials- 450 mya

Geologic Record

Permian (250 million years ago): 90% of marine animals; Pangea merge

Cretaceous (65 million years ago): death of dinosaurs, 50% of marine species; low angle comet or meteor ( ~10 km across)

Mass Extinction

Snowball Earth (latest ~650 mya)

Severe ice ages covered the entire planet

Multicellular organisms survived deep in oceanic thermal vents and clustered together for protection

Meteor impact could cause another