system
Given the following post, respond as if you're commenting on Reddit:
human
How do we measure the age of ice?

I'm explaining (poorly) how climate change is not only real to my grandfather but explaining in laymen's terms how we can measure it. This led to me pointing out a few receding glaciers and he seems to think that ice just comes and goes. How do we know a glacier is old?

E; added *is*
gpt
It's similar to how we know a tree is old by counting the number of rings. When you take a big core out of thick ice, you can see how each layer was deposited year by year, and use this to see how old it is.