system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do old trees (especially olive tree) get such a rough, uneven bark on the trunk ?
gpt
If you look closely at the bark, you’ll see layers. The outer layer of the bark is from when the tree was young and skinny.  As the tree grew fatter, his old layer of bark split open while a new bigger one grew underneath. Then when that new layer gets too small, it splits open in the same place, and this goes on and on over the years, until these split places in the bark become really deep and craggy.