Fossil fuels store sunlight, which derives from plants using energy from the sun for photosynthesis. This light energy remains dormant in fossil fuels and dates back many years. Fossil fuels release this energy upon activation, such as burning.
Fossil fuels include coal, oil and natural gas. They exist as nonrenewable resources, meaning once depleted, their reserves never replenish. Development of Earth's fossil fuels dates back millions of years. These fossils formed from the decomposing remains of plant and animal matter. Coal comes specifically from plant remains, while animal matter creates the other fossil fuels. The energy initially stored in these finite fuels classifies as light energy but undergoes transformations over time and with exposure to air and heat.
Plants and animals initially comprising fossil fuels derived energy from sunlight, which transformed into chemical energy with digestion. This energy transferred to the fuels, releasing from once-living organisms later preserved within rocks. Accumulating pressure from the rocks forming over dead organisms released stored energy, ultimately creating fossil fuels. The rising temperatures resulting from the breakdown of plants and animals into energy classifies as thermal energy, which turns into light energy upon burning of the fossil fuels. These fuels produce energy for many objects, including many types of transportation and electronics.