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The ozone layer

Radiation and the atom · level 2, lesson 4 of 6

A question to start

The Sun gives out far more ultraviolet than reaches the ground. Something high above us soaks most of it up. What?

The idea

High in Earth's air, between about 11 and 50 km up, there is a gas called ozone. It is a kind of oxygen. The air there is spread thin, and the ozone is only a tiny part of it. If all of it were squashed down to the ground, it would make a layer only about as thick as two coins stacked together.

But that thin layer soaks up most of the Sun's harmful ultraviolet, so it never reaches us. It shields plants, animals and people all over the planet.

Some chemicals people made, once used in fridges and spray cans, were found to be destroying ozone. A thin patch, the ozone hole, opened up each spring over Antarctica. In 1987, countries all over the world agreed to stop making those chemicals. It worked: the ozone layer is now slowly recovering, and the hole is expected to heal by about 2070.

the ozone layer, 11 to 50 km upmost ultraviolet stoppedvisible light gets through

Worked examples

1. Two coins. All of Earth's ozone, squashed to the pressure at the ground, would be only about 3 mm thick.

2. How high. A jet airliner flies at about 11 km, near the bottom of the ozone layer. The layer reaches up to about 50 km.

3. Fixing it. After 1987, the harmful chemicals stopped building up in the air, and the ozone hole began to shrink back.

Try it

  1. Where is the ozone layer?
  2. What does it do?
  3. What made the ozone hole?
  4. What did countries agree to do in 1987?
Answers
  1. High in Earth's air, about 11 to 50 km up.
  2. It soaks up most of the Sun's harmful ultraviolet.
  3. Chemicals people made, once used in fridges and spray cans.
  4. Stop making the chemicals that destroy ozone.

Common mistake

"The ozone hole lets in heat." It lets in more ultraviolet, not more heat. It is a different problem from the warming caused by carbon dioxide.

Where it leads