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