system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know that an asteroid killed the dinosaurs?
gpt
1. All the large dinosaur fossils suddenly stopped 66 million years ago.

2. We found a massive asteroid crater dated to 66 million years ago. The crater includes a large amount of iridium, which is uncommon on Earth.

5. A thin layer of iridium is spread all around the planet dated to 66 million years ago. All the dinosaur fossils stop at the iridium layer.