system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why are the craters on the moon flat on the bottom? If an asteroid were to hit the moon, material would be blown out and the crater would be more rounded on the bottom, right?
gpt
Initially, yes. But those craters are very very old and have had time for the material to settle somewhat.

The deepest ones also punched deep enough to expose magma, as in the maria. As a liquid or near-liquid, the magma flowed smoothly to form a flat plain before cooling.