Final answer:
Fossil fuels arise from decayed organic matter of ancient organisms subjected to intense heat and pressure over millions of years, leading to coal, oil, and natural gas formation. Oil and natural gas migrated to form underground reservoirs, while coal was formed from terrestrial plants. This process stored solar energy as hydrocarbons that we now use as energy sources.
Step-by-step explanation:
Origin of Fossil Fuels
Fossil fuels are formed from the decayed organic matter of plants, algae, and cyanobacteria that lived millions of years ago. These organisms were buried under layers of sediment where over time, they were subjected to intense heat and pressure, causing their transformation into coal, oil, and natural gas. Specifically, oil and natural gas originated from massive quantities of microscopic plant and animal life that existed in ancient oceans. As these organisms died, they sank to the sea floor, where they were buried under sediment. Over millions of years, they were subjected to bacterial decomposition, heat, and pressure, leading to the formation of hydrocarbons. In contrast, coal was formed from terrestrial plants that were buried under successive layers of material, undergoing a similar process of decomposition and chemical transformation due to anaerobic conditions.
Each type of fossil fuel—natural gas, oil, and coal—depends on the characteristics of the original organic matter, the duration it was buried, and the specific conditions of temperature and pressure it was exposed to during decomposition. Eventually, the liquid and gaseous hydrocarbons such as oil and natural gas migrated away from their point of origin and became concentrated in different underground reservoirs, often trapped beneath dense rock formations called 'caprocks.' Today, these concentrated deposits are extracted and used as a source of energy.
The energy content of fossil fuels originated from sunlight that was stored by prehistoric plants through photosynthesis. Over geological timescales, this stored energy was 'cooked' at high pressures and temperatures in the absence of oxygen, which now fuels modern society's energy demands.