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• Earth is estimated to be ~4.6byo – Radiometric dating of rocks & meteors • Nebula Hypothesis: – Nebula: cloud of gas & dust in space – Gravity pulled much material together (Sun formed) – Planets: remaining materials • Atmosphere contents: – Ammonia, H2O vapor, Methane (CH4), CO2 • Climate: – Extreme heat due to meteor impacts & volcanic activity • Eventually Cooling: Water vapor condensed (oceans formed) Click on picture to play video clip 1. Miller- Urey Experiment • Hypothesis: Energy from lightning created organic materials from inorganic ingredients • Experimental Set-Up: – Ammonia, H2O vapor, Methane, CO gases added – Electricity added (simulate lightning) • Result: Amino Acids & later nucleotides 2. Meteorite Hypothesis Hypothesis: Amino acids arrived on earth by a meteorite. • Lipid membrane hypothesis • Liposomes – Spheres of lipids – Can form around organic molecules – Hypothesis: 1st cell membranes? • A hypothesis proposes that RNA was the first genetic material. – Ribozymes are RNA molecules that catalyze their own replication. – DNA needs enzymes to replicate itself. • Endosymbiosis is a relationship in which one organism lives within the body of another. • Mitochondria and chloroplasts may have developed through endosymbiosis. • Evolution of sexual reproduction led to increased diversity/variation. • Sexual reproduction may have led to multicellular life. Review • What is a nebula? • What does the nebula hypothesis try to explain? • What materials/ingredients did Miller & Urey use in their experiment? Why these and not other ingredients? • Why was Miller and Urey’s experiment of great importance? • How did eukaryotic cells form? • How would sexual reproduction lead to diversity and multicellular life?