If you hold coal in your hands, you're looking at the remains of carboniferous period trees and plants. In the carboniferous period, the eco system didn't know how to break down tough plant fibers like wood.
The trees that were around in the carboniferous period were nothing like the trees you see today, they were more like ferns. They wold look like ferns with tree sizes stumps.
They were scaly prickly bizarre looking plants like Lepidodendron (scaly tree). They didn't embed their sperm in pollen like modern trees, instead their sperm would swim along standing water on the ground just like animal sperm does today. The trees were often male and female so one tree would make the seeds and the other would make the sperm.
The trouble with these types of trees is they need damp environments to reproduce.
After the carboniferous period in the Permian period, fungus and bacteria emerged that were able to break down tough plant fibers like wood so coal was no longer being created on a large scale.
