12.3 origin of life key concept the origin of life on earth remains a puzzle
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12.3 Origin of Life
KEY CONCEPT The origin of life on Earth remains a puzzle.
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12.3 Origin of Life
NGSSS
•SC.912.L.15.8 Describe the scientific explanations of the origin of life on Earth. (MODERATE)
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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.
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12.3 Origin of Life
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
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12.3 Origin of Life
There are two organic molecule hypotheses.
2. meteorite hypothesis- Amino acids may have arrived on Earth through meteorites or asteroid impact.
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12.3 Origin of Life
• 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.
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12.3 Origin of Life
• There are different hypotheses of early cell structure.– lipid membrane hypothesis- lipid spheres could form
around a variety of organic molecules.
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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.