Headings The Atmosphere Search Questions
History.
The atmosphere is the name given to the gases in the air around the Earth.
The Earth is about 4·6 billion years old (4,600,000,000 years).
In the beginning the Earth was very hot
and molten.
As it cooled, the first solid rock
crust appeared
about 4 billion years ago - see rocks.
The atmosphere at that
time is believed to have been
similar
to the atmospheres of Mars and Venus today.
They would have contained the gases
carbon dioxide, ammonia, methane, hydrogen
and
water vapour.
These gases would have come from
volcanoes.
About 3·8 billion
years ago, the temperature of the Earth
would have cooled to less than
100 °C.
Water vapour in the atmosphere started to condense
and gather on the planet's surface as oceans.
It would have rained for a
very very long
time!
Much of the carbon
dioxide and ammonia
would have dissolved in these
primitive oceans.
It is not known how life began on the Earth
because there is not enough evidence
available.
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 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.
The first
life forms (about 3 billion
years ago) may have been bacteria
which were able to live on
methane and ammonia.
Continued on the next page.
Headings The Atmosphere Search Questions
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