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The Atmosphere

What is the Atmosphere?

The atmosphere is the name
given to the gases in the air around the Earth.

What is the History of the Atmosphere?

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.

The atmosphere at that time is believed to have been similar
to the atmospheres of Mars and Venus today.
The atmosphere 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.

The first life forms appeared over 3 billion years ago.
Continued on the next page.

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