Revise GCSE Physics

Question:How to Scientists find out about the composition of the atmosphere in the past?

In the Polar ice (the ice at the North and South Poles) there are tiny bubble of gas, that are basically samples of the atmosphere from the time when the ice froze.

If you take samples of ice from further down, the gases trapped will be from older times than those found near the surface.

So by taking long ice cores and studying the composition of the gases trapped at different depths we can measure the atmosphere in the past.