Explain how coal deposits are energy sinks.

First, we elaborate the definition of a source and a sink. A source of energy for the earth will be anything that adds energy to the earth, such as the sun. A sink is any substance, material or object that removes energy from the earth.
Therefore, coal is an energy sink in terms of the energy of the earth because it takes a lot of energy for coal to be formed. The conditions under which coal is formed, high pressure and temperature over a long period of time, are energy extensive, making coal an energy sink.