1. Origin of Life on Earth

2. What do we know about early life on Earth?
Evidence from rocks called stromatolites
Consist of banded domes of rock
Similar to layered mats found in salt marshes today

3. Stromatolites
Large mats found at Shark Bay, Western Australia are considered “living stromatolites”

4. Cross section of a stromatolite
Notice the layers of microbes known as fossilized “mats” of bacteria

5. What do we know about early life on Earth?
Evidence in individual fossilized cells suggest life as early as billion years ago
See Fig. 5.2 (text)

6. What do we know about early life on Earth?
Evidence from analysis of ratios of carbon isotopes in ancient rocks (C13, C 12)
Rocks older than 3.85 billion years may had organic life

7. If life existed 3.85 billion years ago…
Would we find traces of it?
No! Why?

8. Tree of life as evidence?

9. Evidence of early life on Earth
Stromatolites
Fossilized cells
Use the tree of life to determine relationships

10. What was the early Earth like?
Water, no land
No oxygen present
No protection from UV radiation
Shallow ponds the home of first life

11. Early life needs better energy source
deep sea vents
Surface hot springs

12. Miller-Urey Experiment
Used flasks to simulate chemical conditions present on Earth
Generated organic molecules…but not enough for life

13. Where could organic compounds come from?
Impacts (asteroids, comets, meteors)
Chemical reactions near deep sea vents

14. What do we have so far? Organic compounds
Environment that can produce these compounds
What else do we need??

15. What type of molecule would be best at replication?
DNA?
RNA?

16. 1980’s discover replicating RNA
Cech and colleagues identify that RNA can self-replicate….acts as enzymes
Called ribozymes

17. If it was an “RNA World”

18. If not “RNA World” then what?
DNA…still have the “chicken and egg problem”
Proteins were first
Double origin, proteins and replication of nucleic acids
Clay crystals serve as scaffolding

19. How can we get to a more “cell-like” model?
Need to confine the organic compounds in membranes
“pre-cells” formed from
Amino acids
Lipids mixed with water

20. Summary of early life…takes many steps
Need materials to form “organic soup”
Generate more complex molecules (polymers)
Membranes formed
Natural selection of RNA leads to DNA model

21. Is this the only idea behind early life on Earth?No
What is panspermia?

22. Evidence to support Panspermia
Organic molecules in meteorites
Microbes can survive moderate time in space

23. When did bacteria evolve compared to other cells?

24. A look at early microbes
General characterisitics

25. Deep Sea vents model early life for microbes

26. Photosynthesis changed the Earth
Organisms could obtain energy from the sunlight
Evolved slowly…first just pigments trap uv light
Purple and green sulfur bacteria are much like early photosynthetic microbes

27. Photosynthesis using water
Evolved 3.5 billion years ago
Earliest fossils resemble modern cyanobacteria (blue-green algae)

28. Cyanobacteria in Lake Sammamish
Sept 1997
Algal bloom of Microcystis aeruginosa