Every time a new layer of water is added on the ice, another latyer of ice forms. The longer this happens (the more layers the ice has) the older the ice is. Similar to trees. The older a tree is, the more rings it has
Layers of ice and tree rings are similar in that they can both record or store data from past environmental conditions. ... Just like the tree rings specific sections represent a specific period of time. Air bubbles trapped in ice provides information on past climates.
