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How did Life Begin on the Earth?
What is the Origin of Life on the Earth?
The first
life forms appeared on Earth over 3·5
billion
years ago.
The atmosphere at that time was very different
from today.
The first
life forms may have been bacteria
which were able to
live on the methane and ammonia in the ancient
atmosphere.
It is not known how life began on the Earth
because
there is not enough
available evidence
from so long ago.
There are many theories
of how life may have started.
Some people believe that life did not begin
on the surface
of the Earth but may have started at a hydrothermal
vent
in mineral rich waters
under the sea at a mid-ocean
ridge.
What did the Experiments by Miller and Urey
show?
An experiment by Miller and Urey
in 1952
tried
to
recreate the conditions which may have
been present
in
the Earth's atmosphere about 3 billion
years ago. They
wanted to see if life could have begun from natural
events.
They used a sealed
and sterile glass flask with the gases
ammonia, methane, hydrogen and
water vapour inside.
They passed electric sparks
(to simulate lightning)
through
the gases for a week. When they analyzed the mixture
they found that many carbon compounds
had formed inside
the flask.
The carbon had come from the methane
gas.
Some of these compounds were found to be amino
acids
which are used by living organisms to
make proteins.
This experiment does not
conclude that life began naturally
on Earth. No one so far has been able to make
living things from simple
elements and compounds.
The experiment does show that complex molecules
like amino
acids can occur spontaneously
in the right conditions. It is
possible that these conditions existed on Earth
a long time ago.
Continued on the next page.
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