1. CH 26: Early Earth and the Origin of Life Presentation by Alisa Gordon, Erica Guo, and Victoria Chen

2. The History of Life: An Introduction Earth was formed about 4.5 billion years ago Life is thought to have formed between 3.5 and 4 billion years ago Evidence? Isotopes in carbon found in 3.8 billion year old rocks in Greenland

3. What was the first life? Prokaryotes were probably the first organisms Evidence through Stromatolites, banded domes of sedimentary rock Stromatolites are similar layered mats in salt marshes formed today by colonies of bacteria. Oldest known fossils of Living organisms are found in 3.5 billion year old Stromatolites in Western Australia

4. Stromatolite

5. The History of life 1. After the Earth’s crust cooled and solidified, we believe that prokaryotes were the first to originate 2. Bacteria and Archaea became the two best thriving prokaryotes (their split happened 3 billion years ago) 3. Evolution of aerobic life began 2.5 billion years ago, thanks to the presence of O2 from early photosynthetic prokaryotes

6. History of Life (continued) 4. Oldest Eukaryotic fossils = 1.7 billion years ago, but evolved hundreds of millions of years before hand -evidence that they evolved from symbiotic communities of prokaryotes 5. Protists: large group of unicellular organisms - Plants, animals, and fungi arose from distinct protists

7. Where they came from

8. History of Life( continued) 6. Oldest animal fossils = 700 million years ago from (specifically, the Precambrian Era) - Fauna not too diverse 7. For 3.5 billion years, life was confined to aquatic environment (90% of its existence)

9. The Origin of Life The first cells may have originated by chemical evolution on a young Earth Life on Earth developed from nonliving materials Lightning, volcanic activity, meteorite bombardment, ultraviolet radiation Created environment in which early stages of biological inception was inevitable

10. How did they evolve? One Hypothesis: Abiotic synthesis and accumulation of small organic molecules Joining of molecules to polymers: proteins, nucleic acids Aggregation of molecules into droplets: Protobionts Origin of heredity

11. Abiotic synthesis of organic monomers 1920 – A. I. Oparin and J. B. S. Haldane Conditions on primitive Earth favored creation of organic compounds Primitive Earth’s atmosphere had less oxidizing atmosphere Making organic molecules was facilitated by intense UV radiation – the earth had a primitive atmosphere

12. Abiotic synthesis of organic monomers 1953 – Stanley Miller and Harold Urey Tested Oparin-Haldane hypothesis Included variety of amino acids and other organic compounds in living organisms Apparatus used to simulate chemical dynamics on primitive Earth Laboratory analogs have produced 20 amino acids found in organisms Many doubt atmosphere was reason for development, believe that submerged volcanoes and deep-sea vents provided the resources needed

14. Laboratory Stimulations Abiotic synthesis of complex organic molecules was bound to happen: Smaller organic polymers (like proteins) had to join No enzymes to catalyze a cell’s reaction, and water dissolves polymers…So how did they? Answer- Polymerization occurs when dilute solutions of organic monomers dripped onto hot sand, clay or rock Using this polymerization method, we can make proteinoids, polypeptides produced by abiotic synthesis.

15. Substrates Clay is important substrate for the polymerization reactions steps to life Concentrates amino acids and other organic molecules and binds them with the clay particles Iron and zinc function like catalysts Alternative to clay: Iron pyrite (Fools gold) Hypothesized to be a substrate by Gunter Wachterhauser

16. Examples

17. Protobionts Protobionts: aggregates of abiotically produced molecules Not capable of reproduction, but have metabolism and excitability Have different internal chemical balance then its environment Coacervates are droplets that reassemble themselves when macromolecules shaken

18. Coacervates

19. More on Protobionts Form spontaneously from abiotically produced organic compounds Have protein membrane that swell or shrink in different salt concentrations Discharge voltage like nerve cells Protobionts that formed long ago though would not have had refined enzymes, which meant they had no inherited instruction