system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do trees get rings that can tell us their age?

How are the rings formed? Also, can you calculate a tree's age by measuring the outside of it?
gpt
Trees grow from the center outward and different factors change the look of what grows. Lighter wood correlates to spring and darker wood correlates to winter (given the dramatic differences in weather between the two seasons). Since each year has either a spring or a winter, all we have to do is count how many winters a tree has been through to give a good estimate of it's age.