1. History of Life on Earth
Chapter 25
Bozeman Tutorial: Origin of Life (14:14)
Bozeman Tutorial: Speciation and Extinction (12:59)

2. Early Earth Conditions
Starting about 3.9 billion years ago, Earth cooled, oceans formed, and atmosphere formed (nitrogen compounds, CO2, methane, ammonia, water vapor, and hydrogen).
1920’s -- Oparin and Haldane: organic molecules could have formed in the “primitive soup” of the oceans with energy from lightning and UV.
Miller and Urey: tested the hypothesis; produced amino acids and other organic molecules.

3. Miller- Urey Experiment

4. Other ideas
Life from space: meteorites containing carbon compounds fell to Earth.
Abiotic synthesis: amino acid polymers from dripping organic monomers onto hot sand or clay.
Protobionts: organic molecules inside a membrane-like structure could have started metabolizing and reproducing.

5. (a) Simple reproduction by liposomes Maltose (b) Simple metabolism
Fig. 25-3
20 µm
Glucose-phosphate
Glucose-phosphate
Phosphatase
Starch
Amylase
Phosphate
Maltose
Figure 25.3 Laboratory versions of protobionts
(a) Simple reproduction by
liposomes
Maltose
(b) Simple metabolism

6. RNA before DNA
RNA can replicate quickly and can act as a catalyst (ribozymes).
DNA later replaced RNA as the main genetic storage molecule (more stable and accurate).

7. Figure 26.11 Abiotic replication of RNA

8. Fossil record illustrates macroevolution
Relative dating: position of fossils in rock strata.
Absolute dating: (doesn’t mean “exact”) gives an age estimation in years.
Radiometric dating is a type of absolute dating using half-lives (decay rate) of radioactive isotopes.
Carbon dating measures C-14 vs C-12 (5,730 years)
Other elements can be used to date rocks/minerals which contain the fossil.

10. Clock analogy for some key events in evolutionary history

11. 3.5 billion years ago
First single-celled organisms: Prokaryotes (bacteria)
Oldest known fossils are stromatolites, layered rocks of prokaryotes and sediment.
Some prokaryotic cells begin photosynthezing (about 2.7 bya) and add oxygen to the atmosphere.
This probably killed many prokaryotes (anaerobes).

12. Stromatolites

13. Evidence of oxygen accumulation from cyanobacteria in banded iron formations

14. 2.1 billion years ago
First eukaryotic cells (with nuclei and organelles)
Endosymbiosis: Organelles (like mitochondria and chloroplasts) may have been prokaryotes that were engulfed by other prokaryotes.
Mitochondria and chloroplast contain their own DNA and enzymes and can self- replicate.

16. 1.5 billion years ago First multi-cellular eukaryotes: Algae
A series of ice ages probably limited diversity until about 565 mya.
Cambrian explosion: (535 – 525 mya) Many groups of aquatic animals alive today appear in the fossil record.
500 mya: Colonization of land by larger multicellular eukaryotes (plants, animals, and fungi).

18. The Big Five
Five mass extinctions are documented in the fossil record.
Ordovician-Silurian: (443 mya) 85% of sea life was wiped out; ice age, fall in sea level, ocean chemistry altered.
Late Devonian: (359 mya) 75% of all species died out; oxygen depletion, change in sea level, climate change.
Permian: (250 mya) 96% of species disappeared; intense volcanic activity, climate change, oxygen depletion.

19. The Big Five cont.
Triassic-Jurassic : (200 mya) Half of species became extinct; climate change, flood basalt eruptions.
Cretaceous: (65 mya) half of marine species and many terrestrial forms, including most dinosaurs; asteroid impact, blocked sunlight.
Extinctions opened niches to organisms which survived, leading to adaptive radiation. (Mammals greatly developed after dinosaurs died.)