What is the correct sequence of coal formation?

Coal formation begins with the decay of plants and animals in the absence of oxygen. Bacteria release oxygen and hydrogen and concentrate carbon. Impurities are removed over time, and the weight of sediment compresses the matter, leaving a material with a very high carbon concentration.

Most coal was formed about 300 million years ago. During this time, Earth was primarily covered by swamps. Dying plants and trees sank into these swamps. As the climate changed and swamps dried up, rivers and streams deposited sediment on top of these remains, creating large coal beds. Coal production continues in swampy areas of Earth, with a completion date millions of years in the future.