So coal has really interesting history. It was all made in a very short timeframe by geological measure, about 30 million years. It was made when trees first grew. The strength member of trees, lignin, didn't have anything that could eat it or decompose it so it just lay where it fell. Sometimes thousands of feet of undecomposed trees just getting buried under the blowing sands. All of that sequestered carbon was laying in the ground instead of being in the air heating up the atmosphere was causing an ice age that lasted until a fungus developed that could eat lignin and release the carbon for use by plants.
One of the most interesting things about it is that we're reproducing the same system with plastics. The plastic is sequestering the carbon in a form that doesn't have anything capable of decomposing it. If we make enough plastic we could cause another ice age.