Throughout our planet's history, global temperatures have risen and fallen naturally. But it has never become too hot or
too cold for life to exist. That's because Earth
is wrapped in its own protective blanket of air, a mixture of gases called the atmosphere.
The atmosphere lets in energy from the Sun. Gases in the atmosphere absorb and keep just enough heat for plants and animals to live. This process is called the greenhouse effect, because the
atmosphere holds in heat like the clear walls of a greenhouse.
The heat-absorbing gases in the atmosphere are called greenhouse gases. Some of the main greenhouse gases include carbon dioxide, water vapor, methane, and ozone. And the more greenhouse
gases there are, the warmer Earth gets.
