[navane]

They match the ice samples up with tree rings. There exists tree ring data of 7k+ years, the ice contains more info, but the tree rings allow for absolute pinpointing on a year. They match them on common info.

I am reading "tree story" by valerie trout.

[physicles]

My understanding was that dendrochronology records go back about 12k years. Is there anything about that in the book you’re reading?

[navane]

I had forgotten the exact number, i knew it was at least 7k. I didnt want to lie in my comment, but im almost sure you are right.

Im at work right now so cant look it up.