1. 12.3 Origin of Life 12.3: The Origin of Life How do scientists think Earth formed and life on Earth began?

2. 12.3 Origin of Life There have been many hypotheses of Earth’s origins. The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis. –Supported by computer models (math) and observations made by Hubble space telescope –Says that our solar system started as a cloud of gas. See Video (link)link

3. 12.3 Origin of Life Gravity caused the gas and dust particles in a nebula to condense. As it condensed, it began to spin. (ice skater) The faster it spun, the flatter it got (pizza dough) Particles collided and grew into planets, comets and asteroids.

4. 12.3 Origin of Life It was very hot! But as Earth cooled, water vapor condensed and formed the oceans. Earth was very different billions of years ago.

5. 12.3 Origin of Life Several sets of hypotheses propose how life began on Earth. There are two major hypotheses organic molecule hypotheses –Miller-Urey experiment Electricity from lightening caused organic molecules (the molecules of life) to form from inorganic molecules in the oceans electrodes heat source amino acids water “atmosphere” “ocean”

6. 12.3 Origin of Life Meteorite Hypothesis –Some meteorites found and studied today contain organic compounds. –Some scientists think that the organic molecules that helped create life came from meteorites.

7. 12.3 Origin of Life There are different hypotheses of early cell structure. –Iron-sulfide bubbles hypothesis Chimney-like structures form when hot iron sulfide rises and solidifies William Martin proposed that these chimney-like structures acted as the first cell membranes, providing a protective place for organic molecules to form Once the right ingredients came together, the first true cell membranes formed and microbes were allowed to leave the compartments.

8. 12.3 Origin of Life Lipid membrane hypothesis Lipid molecules spontaneously form membrane enclosed spheres (called liposomes) These liposomes formed around amino acids, fatty solids, sugars, and nucleotides, separating the organic molecules from the environment

9. 12.3 Origin of Life A hypothesis proposes that RNA was the first genetic material. –DNA (genetic material)needs enzymes to replicate itself. –RNA is the original genetic material that does not need enzymes to help it replicate