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

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!!!!

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

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

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

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!

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

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

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

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

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!

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