What sort of historical data can a glacier provide through an ice core?

past temperature, composition of gases in the atmosphere

Explanation:

Cylindrical cones can be drilled out from the core of glaciers to calculate past temperatures. The air bubbles in the cones can also be used to determine the composition of air in the past yars. This information provides us a means to analyze the trend of global warming and change in concentratinos of green house gases over the years.