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Origin of Life on Earth What do we know about early life on Earth? • Evidence from rocks called stromatolites • Consist of banded domes of rock • Similar to layered mats found in salt marshes today Stromatolites • Large mats found at Shark Bay, Western Australia are considered “living stromatolites” Cross section of a stromatolite • Notice the layers of microbes known as fossilized “mats” of bacteria What do we know about early life on Earth? • Evidence in individual fossilized cells suggest life as early as 3.2-3.5 billion years ago • See Fig. 5.2 (text) What do we know about early life on Earth? • Evidence from analysis of ratios of carbon isotopes in ancient rocks (C13, C 12) • Rocks older than 3.85 billion years may had organic life If life existed 3.85 billion years ago… • Would we find traces of it? • No! Why? Tree of life as evidence? Evidence of early life on Earth • Stromatolites • Fossilized cells • Use the tree of life to determine relationships What was the early Earth like? • • • • Water, no land No oxygen present No protection from UV radiation Shallow ponds the home of first life Early life needs better energy source • deep sea vents • http://www.ocean.udel.edu/deepsea /level-1/geology/smoker.mov • Surface hot springs Miller-Urey Experiment • Used flasks to simulate chemical conditions present on Earth • Generated organic molecules…but not enough for life Where could organic compounds come from? • Impacts (asteroids, comets, meteors) • Chemical reactions near deep sea vents What do we have so far? • Organic compounds • Environment that can produce these compounds • What else do we need?? What type of molecule would be best at replication? • DNA? • RNA? 1980’s discover replicating RNA • Cech and colleagues identify that RNA can self-replicate….acts as enzymes • Called ribozymes If it was an “RNA World” If not “RNA World” then what? • DNA…still have the “chicken and egg problem” • Proteins were first • Double origin, proteins and replication of nucleic acids • Clay crystals serve as scaffolding How can we get to a more “celllike” model? • Need to confine the organic compounds in membranes • “pre-cells” formed from – Amino acids – Lipids mixed with water Summary of early life…takes many steps • Need materials to form “organic soup” • Generate more complex molecules (polymers) • Membranes formed • Natural selection of RNA leads to DNA model Is this the only idea behind early life on Earth? • No • What is panspermia? Evidence to support Panspermia • Organic molecules in meteorites • Microbes can survive moderate time in space When did bacteria evolve compared to other cells? A look at early microbes • General characterisitics Deep Sea vents model early life for microbes Photosynthesis changed the Earth • Organisms could obtain energy from the sunlight • Evolved slowly…first just pigments trap uv light • Purple and green sulfur bacteria are much like early photosynthetic microbes Photosynthesis using water • Evolved 3.5 billion years ago • Earliest fossils resemble modern cyanobacteria (bluegreen algae) Cyanobacteria in Lake Sammamish • Sept 1997 • Algal bloom of Microcystis aeruginosa