What is similar about the way petroleum and coal form? what is different?

The similarity between petroleum and coal is that they are both fossil fuels, which means they are formed from dead organic matter. the different between them is that coal contains carbon in its pure form, while petroleum and natural gas are hydrocarbons formed during the decaying process. Also coal is the remain of trees, ferns, and other plants that lived million of years ago while petroleum is the remains of millions of tiny plants and animals that lived in the sea. 

Ibelieve the answer is a-broad because that is a leafed plant.