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