1. Notes package (chapter 26)
The Tree of Life
Notes package (chapter 26)

2. Miller-Urey Experiment
Steps
Results
Water = Primeval “sea”
Electrodes = sparks mimic lightning
Sphere = simulated “atmosphere”
Condenser = cooled atmosphere; “rain” & dissolved compounds fall into the sea
Variety of organic compounds identified (ex. some amino acids & complex hydrocarbons)
Could form the basis of LIFE!!!!

4. Protobionts Abiotically produced molecules surrounded by membrane
Could have been spontaneously produced from organic compounds

5. Ex. Liposomes
When lipids are added to water, small droplets form (like the lipid bilayer of cell membranes)
Permeable to water & other organic molecules

6. What does that mean??
Could serve as the precursors to basic PROKARYOTIC cells
Ex. Bacteria (have no membranous organelles inside the cell)

7. Radiometric Dating & Halflife
Based on decay of radioactive isotopes
Each isotope has a fixed rate of decay
# of years it takes for 50% of the original sample to decay
Can be used to date fossils in rocks
Ex. Carbon-14 half-life is 5,730 years  can date fossils up to 75,000 years old!

8. A Question for you…
How do we use potassium-40 to date older fossils? (page 517)
Potassium-40 has a very long half life (~1.2 x 109 years)
Degrades into Argon-40 which remains locked in rock mineral deposits
Comparing K-40 and Ar-40 ratios can be used to date very old rocks

9. Geologic Record Divides Earth’s history into distinct eons
End of each eon is defined by a mass extinction event!

10. Mass Extinctions
Peaks in the extinction rate followed by increase in the # of taxonomic families
Adaptive Radiation will fill unoccupied niches

11. Stromatolites… Pretty Cool Structures 
Composed of layers of bacteria (1st prokaryotes) & sediment
Fossilized stromatolites dated to 3.5 billion years ago!
Provides evidence for early life at ~3.9 billion years ago

12. The Oxygen Revolution Earth’s early atmosphere had very limited oxygen
First bacterial cells were anaerobic (did not need oxygen)
Some bacteria developed the ability to photosynthesize
This released huge quantities of oxygen into the atmosphere
Lead to first mass extinction event of anaerobic bacteria!

13. Endosymbiosis (question #7)
Endosymbiosis: Cell living inside a host cell
Prokaryotic cells incorporated into larger host cell by being engulfed
Cells developed primitive nucleus to replicate
Engulfing of aerobic heterotrophic bacteria  MITOCHONDRIA
Engulfing autotrophic photosynthetic bacteria  CHLOROPLASTS