system
Given the following post, respond as if you're commenting on Reddit:
human
Was there oil during the dinosaur era?

As in car oil that comes from fossils? Was there sufficient oil in the ground millions if years ago?
gpt
Yes, there was.  Much of our 'fossil fuel' comes from a time period known as the Carboniferous, which was about 300 - 360 million years ago, well before the time of the dinosaurs.  This period is called the Carboniferous precisely because there's a high abundance of carbon in the rock record from that time.  This is often preserved as coal or petroleum.  Most of this carbon material derives from plants and algae, rather than the more familiar fossils of vertebrate animals.

Dinosaurs did not appear until the middle Triassic about 230 million years ago.