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

2. Earth was very different billions of years ago.
There have been many hypotheses of Earth’s origins.
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)

3. Eventually Cooling: Water vapor condensed (oceans formed)
Ancient Earth
Atmosphere contents:
Ammonia, H2O vapor, Methane, H2, CO2
Climate:
Extreme heat due to meteor impacts & volcanic activity
Eventually Cooling: Water vapor condensed (oceans formed)
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4. Several sets of hypotheses propose how life began on Earth.
There are two organic molecule hypotheses.
Miller-Urey experiment
electrodes
heat source
amino acids
water
“atmosphere”
“ocean”
Energy from lightning created organic materials from inorganic ingredients
Result: amino acids and later nucleotides
meteorite hypothesis
amino acids may have arrived on Earth through meteorite or asteroid impacts (outer space).

5. There are different hypotheses of early cell structure.
iron-sulfide bubbles hypothesis
lipid membrane hypothesis
compartments of chimney like structures on the ocean floor.
The compartments acted as the first cell membranes.
Lipid spheres, or liposomes, could form around a variety of organic molecules, acting as early cell membranes.

6. RNA as Early Genetic Material
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.