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

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KEY CONCEPT The origin of life on Earth remains
a puzzle.
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Earth was very different billions of years ago.

• There have been many hypotheses of Earths
  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)

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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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Several sets of hypotheses propose how life began
on Earth.

• There are two organic molecule hypotheses.
• Miller-Urey experiment

• 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).

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• There are different hypotheses of early cell
  structure.

• iron-sulfide bubbles hypothesis

• compartments of chimney like structures on the
  ocean floor.
• The compartments acted as the first cell
  membranes.

• lipid membrane hypothesis

• Lipid spheres, or liposomes, could form around a
  variety of organic molecules, acting as early
  cell membranes.

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• 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.