Question

how coal was formed under the earth

Answer 1

Most of the coal we use now was formed about 300 million years ago, when much of the earth was covered by steamy swamps. As plants and trees died, their remains sank to the bottom of the swampy areas, making layers and layers of plant material and eventually forming a soggy, thick material called PEAT.

Answer 2

Coal was formed by the decomposition of large land plants and treed buried under the earth millions of years ago. Due to high temperature and high pressure inside the earth and in the absence of air wood was converted into coal.