12.3 Origin of Life KEY CONCEPT The origin of life on Earth remains a puzzle.

12.3 Origin of Life Earth was very different billions of years ago. There have been many hypotheses of Earth’s origins. The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis.

12.3 Origin of Life Several sets of hypotheses propose how life began on Earth. There are two organic molecule hypotheses. –Miller-Urey experiment –meteorite hypothesis electrodes heat source amino acids water “atmosphere” “ocean”

12.3 Origin of Life Miller Urey Demonstrated that organic compounds could be made by passing an electrical current, to simulate lightning, through a closed system that held a mixture of gases.

12.3 Origin of Life Meteorite Hypothesis Amino acids may have arrived on Earth through meteorite or asteroid impacts.

12.3 Origin of Life There are different hypotheses of early cell structure. –iron-sulfide bubbles hypothesis

12.3 Origin of Life Iron Sulfide Bubble Model Biological molecules combined in compartments of chimney like structures on the ocean floor. The compartments acted as the first cell membranes.

12.3 Origin of Life There are different hypotheses of early cell structure. –lipid membrane hypothesis

12.3 Origin of Life Lipid Membrane Hypothesis Lipid spheres, or liposomes, could form around a variety of organic molecules, acting as early cell membranes

12.3 Origin of Life 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.