BIO 1108 1st Edition Lecture 2 Outline of last Lecture I II III IV V VI Evolution Mechanisms of evolution Natural Selection a Examples explanations and definition Migration gene flow a Examples explanations and definition Genetic Drif a Examples explanations and definition Mutation a Examples explanations and definition Outline of Current lecture I II III IV V VI VII VIII I II Brief History of life 4 3 8 billion years ago 3 5 billion years ago Likely properties of protocells Metabolic diversity of prokaryotes Rise in Oxygen levels Rise in Oxygen production Endosymbiosis Brief History of life Universe 10 20 billion years old Solar system 4 5 billion years old Earth 4 5 billion years old 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 Edition III IV V 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 rises 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 itself Metabolic diversity of prokaryotes Metabolic 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 Edition VI These are either saprobes use dead organic matter or parasites use living organisms as a source 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 VII VIII 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 mya 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 heterotrophs Endosymbiosis BIO 1108 1st Edition Where did Eukaryotes come from The Endosymbiont Theory was first proposed by Lynn Margulis in 1967 Her predictons could only be tested in 1980s It was published in her 1981 book Symbiosis in Cell Evolution