Fossil fuels generally include coal, oil and gas which have formed through natural resources such as the decomposition of buried dead organisms.  Fossil fuels are non-renewable resources because they take millions of years to form.

Coal is a solid fossil fuel formed over millions of years by the decay of land vegetation. Over time, successive layers of vegetation become buried, compacted and heated. This process leads to the deposits turning into coal. Coal is widely used in the generation of electricity and is a highly concentrated energy source.
Oil is formed from the decay of marine micro organisms deposited on the sea floor. As the micro animal and plant remains accumulate over millions of years, they gradually infiltrate the microscopic cavities of the sea floor sediment and rock where they decay. The resulting oil remains trapped in these spaces, forming oil reserves which can be extracted through large drilling platforms. Gas is produced in very much the same way as oil.

The main concerns associated with fossil fuels are the environmental pollution issues and the effects on global warming. Burning coal produces more carbon dioxide than burning oil or gas. It also produces sulphur dioxide, an acidic gas that contributes to the formation of acid rain. One of the main problems associated with acid rain is the effects it has on deforestation.  Acid rain weakens trees by damaging their leaves, limiting the nutrients available to them, or exposing them to toxic substances slowly released from the soil. Eventually this leads to the destruction of the trees and resulting in damage to the quality of the land.

Deforestation is also often caused through the clearing of forests on a large scale for oil and coal mining exploitation. Often the requirement for land for a big opencast coal projects are quite large and much of the forest area are converted into a mining field.  Consequently, large forest areas are deforested to make a way for large opencast coal mines.

There are many negative effects on the environment from de-forestation. The most dramatic impact is the loss of habitat for millions of species. Deforestation also drives climate change. Forest soils are moist, but without trees to protect them from the sun they can dry out very quickly. Trees also play a role in the water cycle by returning water vapor back into the atmosphere. Without trees to fill these roles, many forest lands can become desert lands. Trees also play a critical role in absorbing the greenhouse gases that contribute to global warming. If there are fewer forests, larger amounts of greenhouse gases will enter the atmosphere, increasing the effects of global warming.