Cheryl Burdeniuk, age 12, of Winnipeg, Manitoba, Canada, for her question:
WHY IS OIL FOUND ONLY IN SOME PARTS OF THE WORLD?
Oil fields in many parts of the world are the starting points of petroleum, a material that is one of man's most useful fuels. Most important fuel product made from petroleum is gasoline which powers our cars and trucks. Jet fuel, used to send our airplanes to all corners of the earth, also comes from petroleum and so does diesel oil, used to power railroad locomotives.
Oil comes from pools that can be found underground in certain types of rock formations. These rock formations are found in many parts of the world under widely varying conditions of land and climate.
Today oil is being pumped from the earth below farm land, prairies, jungles, swamps, marshes, mountains and even the ocean floors.
It is true that oil can be found underground only in certain locations in many parts of the world. No one is absolutely certain how petroleum was formed.
Most scientists say the organic theory on how petroleum was formed is the correct theory. They say that petroleum was formed through millions of years in prehistoric oceans that covered many parts of the earth. Small animals and tiny plants lived in shallow water and along the coasts, as they do today. As these animals and plants died, their remains settled on the muddy bottoms of the oceans.
Mud and sand, called sediments, drifted down over the plant and animal matter. As these sediments became stacked, their weight pressed them into hard, compact layers of sedimentary rock. During this process, bacteria, heat, pressure and other natural forces changed the plant and animal remains into oil and natural gas.,
Drops of oil and bubbles of gas moved from the mud beds in which they were formed into other sedimentary rocks, usually sandstone or limestone. These porous rocks contained small openings through which the oil moved.
After millions of years, layers of less porous sedimentary rock formed above the rock beds. This rock sealed the oil and gas into underground pools. Later, ancient seas drained away through movements of the earth's crust and dry land appeared above many of the petroleum deposits.
Although oil is found in most parts of the world it is located in pools underground only where a prehistoric ocean was once located.
Not all oil comes from underground pools, however. Some is found in oil shale, a rock made of compressed layers of clay or silt and minerals. This shale doesn't contain oil but it does have a solid material called kerogen. Oil can be obtained from the kerogen by heating crushed shale to about 900 degrees Fahrenheit.
Large oil shale deposits are found in Colorado, Utah and Wyoming in the United States.