Why is the Greenland ice sheet so important to understanding Earth's past climate?

Greenland ice sheets are important in understanding Earth's past climate due to how the ice sheets form. They form when it is cold enough for the snow to stay in place for many years, which slowly becomes compressed as each snowfall occurs and buries it. After time, it turns into ice, showing that took thousands of years to form.

When a large amount of the ice sheet is extracted, scientist are able to witness the layers as well as as study the trapped gasses, dust, and frozen water in them to reconstruct how the Earth's climate and atmosphere must've been in the past.