3. Earth was very different billions of years ago 1. The most widely accepted hypothesis is the nebula hypothesis. The solar system formed by a condensing nebula (a cloud of gas and dust in space) There have been many hypotheses of Earth’s origins.

4. Atmosphere contents: – Ammonia, H 2 O vapor, Methane, H 2, CO 2 Climate: – Extreme heat due to meteor impacts & volcanic activity Eventually Cooling: Water vapor condensed (oceans formed) Click on picture to play video clip

5. There are two organic molecule hypotheses: electrodes heat source amino acids water “atmosphere” “ocean” 1. Miller-Urey Experiment Energy from lightning created organic materials from inorganic ingredients Result: amino acids and later nucleotides 2. Meteorite Hypothesis Amino acids may have arrived on Earth through meteorite or asteroid impacts (outer space). 90 amino acids were found from this meteorite, only 19 of them can be found on Earth.

6. There are different hypotheses of early cell structure 1. Iron-sulfide Bubbles Hypothesis: Compartments of chimney like structures on the ocean floor. The compartments acted as the first cell membranes. 2. Lipid Membrane Hypothesis Lipid spheres, or liposomes, could form around a variety of organic molecules, acting as early cell membranes.

7. Ribozymes are RNA molecules that catalyze their own replication. DNA needs enzymes to replicate itself.

8. Endosymbiosis is a relationship in which one organism lives within the body of another. – Mitochondria and chloroplasts may have developed through endosymbiosis.

9. Genetic variation is an advantage of sexual reproduction. Sexual reproduction may have led to the evolution of multicellular life.