Lecture 2Outline of last LectureI. EvolutionII. Mechanisms of evolutionIII. Natural Selectiona. Examples, explanations, and definition IV. Migration (gene flow)a. Examples, explanations, and definition V. Genetic Drifa. Examples, explanations, and definition VI. Mutation a. Examples, explanations, and definition Outline of Current lectureI. Brief History of lifeII. 4-3.8 billion years agoIII. 3.5 billion years agoIV. Likely properties of protocellsV. Metabolic diversity of prokaryotesVI. Rise in Oxygen levelsVII. Rise in Oxygen productionVIII. EndosymbiosisI. Brief History of life- Universe: 10-20 billion years old- Solar system: 4.5 billion years old- Earth: 4.5 billion years oldII. 4-3.8 billion years ago- ~3.8 bya: Bombardment from outer space ceases, crust cools and solidifies  Oldest known rocks form on Earth surface Atmosphere: Hot! Carbon monoxide (CO) Carbon dioxide (CO2) Nitrogen (N2) Water vapor (H2O) NO FREE OXYGEN BIO 1108 1st EditionIII. 3.5 billion years ago- ~3.5 bya: Evidence for Bacteria • Major molecular building blocks of life Membranes RNA DNA Proteins- First fossil Prokaryotes Stromatolites Cyanobacterial activity: layers of thin films of cells form layered sediments Found today and as fossils Earliest fossils resemble modern cyanobacteria- Evolution of bacteria with diverse chemistry: ~3 bya:rise of Cyanobacteria (diversification and proliferation of photosynthetic bacteria)…O2 production Oxygen production risesIV. Likely properties of protocells- Membrane-like structures surrounding “protocells” form spontaneously from simple precursor molecules  lipids form liposomes in water  chemistry can be different inside and out - “RNA World” Hypothesis  RNA can form spontaneously from simple precursor molecules  contains genetic information  catalytic activity & can replicate itselfV. Metabolic diversity of prokaryotesMetabolic diversity is greater among prokaryotes than in all eukaryotes combined. Four major groups (depending on how they obtain energy (from light or chemicals) and carbon (from CO2 or organic molecules) :Early Earth:- Chemoautotrophs are organisms that need only CO2 as a carbon source and obtain energy by oxidizing inorganic compounds such as H2S, NH3 and Fe2+- Photoautotrophs need only light energy and CO2 as a source of carbon in order to synthesize their organic compounds and ATP. Later (once organic molecules were available) in addition:- Photoheterotrophs must obtain their carbon in a more complex organic form (generated by other organisms) and use light energy to generate ATP.- Chemoheterotrophs must obtain complex organic molecules as both a source of energy and as a source of carbon BIO 1108 1st EditionThese are either saprobes: use dead organic matter or parasites: use living organisms asa source. VI. Rise in Oxygen levels- Poison for many anaerobes: mass extinctions? - Survivors have antioxidants and special enzymes to neutralize oxygen - These oxygen-binding molecules could later evolve functions as oxygen carriers in aerobic organisms - Interactions between prokaryotes with different chemistry:- Until ~2.2 bya: stable O2 levels ~ 1% of today - ~ 2.2 bya: First ice age: snowball earth  Hypothesis: oxygen oxidizes methane (green house gas): cooling surface temperatures cause ice age  Volcanic activities: cause CO2 levels to increase  Greenhouse effect: warming of surface - Bloom of cyanobacteria: O2 levels increase ~ 5-18 % of today - Evolution of eukaryotes (~2.1 bya) - Evolution of multicellular eukaryotes (~1.5 bya) - O2 levels close to present day levels: 750 mya- 700 mya: start of Cambrian explosion - Another series of ice ages starting ~750 myaVII. Rise in Oxygen production- O2 oxidizes soluble iron (Fe2+) to insoluble Fe3+ compounds (rust)- Iron oxides (rust) precipitated into rocks (banded iron formations) particularly abundant around 2.7-2.4 billion years ago- Then O2 could accumulate (0.1-0.2%) 2.4-0.8 billion years ago- Poison for many anaerobes: mass extinctions?  Survivors have antioxidants and special enzymes to neutralize oxygen  These oxygen-binding molecules could later evolve functions as oxygen carriers in aerobic organisms - Adaptive radiation of aerobic Bacteria & Archaea into new environments - Leads to evolution of metabolic diversity among prokaryotes - O2 levels stabilize: not much free O2 yet  cynaobacteria vs aerobic heterotrophsVIII. Endosymbiosis BIO 1108 1st EditionWhere did Eukaryotes come from?The Endosymbiont Theory was first proposed by Lynn Margulis in 1967. Her predictonscould only be tested in 1980s. It was published in her 1981 book “Symbiosis in Cell Evolution” BIO 1108 1st