majalahinggris.com – Coal is a fossil fuel created from the remains of plants that lived and died about 100 to 400 million years ago when parts of the earth were covered with huge swampy forests. Coal is classified as a nonrenewable energy source because it takes millions of years to form.
The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago. All living plants store energy from the sun through a process known as photosynthesis. After the plants die, this energy is released as the plants’ decay. Under conditions favorable to coal formation, however, the decay process is interrupted, preventing the further release of the stored solar energy.
Millions of years ago, dead plant matter fell into the swampy water, and over the years, a thick layer of dead plants lay decaying at the bottom of the swamps. Over time, the surface and climate of the earth changed, and more water and dirt washed in, halting the decay process. The weight of the top layers of water and dirt packed down the lower layers of plant matter. Under heat and pressure, this plant matter underwent chemical and physical changes, pushing out oxygen and leaving rich hydrocarbon deposits. What once had been plants gradually turned into coal.
Seams of coal – ranging in thickness from a fraction of an inch to hundreds of feet – may represent hundreds or even thousands of years of plant growth. One important coal seam, the seven-foot thick Pittsburgh seam, may represent 2,000 years of rapid plant growth. One acre of this seam contains about 14,000 tons of coal, enough to supply the electric power needs of 4,500 American homes for one year.
