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Ch. 15 Evolution
Section 1: Origin of Life
How did life on Earth begin?
Let’s first start with a small discussion that relates
to this chapter. Raise your hand and let me know
your opinion(s) on any of the following questions.
How did our universe begin?
How did life begin on Earth?
Where did our human ancestors come from?
4 processes needed for life on Earth:
1. ORGANIC MOLECULES - When Earth was
formed, it consisted of rock, minerals, gases,
and water….so where did the organic
molecules come from?
2. ABILITY TO FORM POLYMERS - Furthermore,
monomers (basic organic molecules like amino
acids and monosaccharides) are not enough
to make complex organisms, these molecules
must first combine to become polymers
4 processes needed for life on Earth:
3. ABILITY TO REPRODUCE - Organisms must selfreplicate, but early organisms most likely did not
have “modern” DNA or RNA or the enzymes
necessary to carry out the functions
4. PACKAGING MOLECULES IN MEMBRANES - Earth
had water, but the presents of water often makes
polymers break down into monomers (hydrolysis
reactions) … this makes it hard to make and keep
complex molecules
Miller Urey Experiment
• Experiment performed by Stanley Miller and Harold Urey at
the University of Chicago 1953
•Added gases that they thought
would have been present on
ancient Earth including methane,
hydrogen, ammonia
•Added water, which was heated
and cooled to simulate water cycle
•Exposed apparatus to UV radiation
since no ozone layer yet
•Electric sparks simulated
lightening
Results of Experiment
• After one week, organic compounds such as amino
acids had formed as well as certain sugars and
nucleic acids
• This helps explain the potential of how the first
organic molecules formed, but we are still left with
the other 3 problems including complex organic
molecules, self-replicating molecules, and the
membrane dilemma
Potential Locations of
Synthesis of Organic
Molecules:
1. In space
• scientists have studied spectral lines of distant
clouds of dust particles and have spotted glycine
(simplest amino acid)
• Further studies in low pressure, low temp
environments have led to synthesis of amino acids
• Also idea that comets could have brought amino
acids in massive bombardment ~ 4 bya
• Idea that organic molecules may have come from
space is called Panspermia
2. In alternating wet and dry conditions
• Areas like seashores, flood plains, intertidal zones
(ex: famous ancient fossil of stromatolites found in
intertidal areas; helps to suggest that these
conditions were favorable to ancient life)
3. Near volcanoes
• Has necessary gases including
water vapor as well as a warm
environment
4. Near hydrothermal vents
• The vents release hot water,
minerals from Earth’s crust,
and gases