There was a 20 million year window, in which dead trees just piled up. Nothing could digest the lignin. This is how germany's brown coal reserves came to be.

The sharks thing actually leads to another fun fact:

Sharks are older than some of the north star, as the noth star is actually a binary star system next to a solo star. I forget what part it's actually older than, so here's the source.

https://youtu.be/-YU8Vt9VpbE