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

NGSSS SC.912.L.15.8 Describe the scientific explanations of the origin of life on Earth. (MODERATE)

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.

Several sets of hypotheses propose how life began on Earth. There are two organic molecule hypotheses. 1.Miller-Urey experiment- Demonstrated that organic compounds could be made by passing a electric current (simulating lightning) through a closed system that held a mixture of gasses and water. electrodes heat source amino acids water “atmosphere” “ocean” Gasses thought to be on early earth: ammonia, methane, hydrogen, Carbon dioxide. No oxygen

There are two organic molecule hypotheses. 2. meteorite hypothesis- Amino acids may have arrived on Earth through meteorites or asteroid impact.

There are different hypotheses of early cell structure. iron-sulfide bubbles hypothesis- Biological molecule combined in in compartments of hydrothermal vents where organic molecules were concentrated - the walls of the compartment formed the cell membranes.

There are different hypotheses of early cell structure. lipid membrane hypothesis- lipid spheres could form around a variety of organic molecules.

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.