Vicky Teinaki, of Whangarei Primary School, asks :-

How did Earth get it's ozone layer?

Steve Wood, a physicist with the National Institute of Water and Atmosphere, who is wintering over in the Antarctic while studying the Ozone layer, responded.

Scientists aren't sure exactly how the Earth's atmosphere was formed.

It is made up of gases released by the surface of the Earth, by early volcanoes and the life that has developed on Earth.

As soon as the first plant life (probably some early form of algae) started making oxygen by photosynthesis then an ozone layer would form. This is because the ultraviolet light from the sun splits the two atoms in oxygen molecules and an individual oxygen atom combines with an oxygen molecule to form an ozone molecule. The early life forms on the earth were shielded from ultraviolet light by being in water but once there was ozone in the atmosphere it did the shielding. Ozone is the only gas that absorbs the near ultraviolet wavelengths that can break chemical bonds and hence ultraviolet light is dangerous to living tissue. We are now dependent on the existence of the ozone layer for our survival.

A lot of things vary the amount of ozone in the atmosphere at different places and different times of the year. We get worried when something happens to reduce the amount of ozone. I'm studying how ozone loss happens in the Antarctic where very low ozone amounts occur each spring. It helps us understand if such a big loss could happen in other places.