The remains of plants and animals that lived long ago are called fossils. The term comes from a Latin word meaning “to dig.There are different kinds of fossils. In hot and dry places, sometimes the actual bone or tooth of an extinct animal gets preserved. In moist places, the original bone material is replaced, cell by cell, with minerals.One kind of fossil is called a stone core. For example, the shell of an ancient snail might fill with fine sand after the animal dies. The shell might then become buried, where it decays and leaves a hollow mold. This mold might then fill up with mineral matter and form a cast of the animal's shape, or a stone core fossil.
Sometimes a fossil is simply a print of prehistoric animals. With this type of fossil, the delicate imprint of a leaf or blossom on some soft material hardens into solid rock.Another kind of fossil is called an inclusion. In this case, the object is usually small, such as an insect or a small piece of a plant. The object becomes embedded in flowing resin, which is the sticky substance of a pine tree. The resin fossilizes, and the embedded insect becomes a fossil too.Finally, there are pseudofossils, or false fossils. These are mineral forms that look like fossils. Sometimes water enters cracks in rocks like slate. The minerals from the water are deposited there and look like fossil moss or fossil ferns. Such pseudofossils are called dendrites.For an organism to be preserved, two conditions must be met. One, the organism must be quickly buried to delay the process of decomposition and prevent the attack of scavengers. Two, the organism must have hard body parts that can be fossilized.Most animal fossils are those of creatures that died an accidental death in such a way that their bodies were quickly covered by the earth. For example, an animal that drowned near a river mouth and was swept out to sea and covered with sand and silt may have become fossilized.A great majority of fossils are preserved in water because the remains on land are more easily destroyed. Also, the conditions at the bottom of the seas or other bodies of water are especially favorable for preservation. This is because, except for bacteria, there are no marine creatures to destroy the remains.Rancho La Brea, in Los Angeles, California, is the most spectacular fossil area in the United States. Its sticky pools of oil and asphalt trapped thousands of prehistoric animals. Saber-toothed tigers, dinosaurs, giant wolves, short-faced bears, and horses have been uncovered there. Although the flesh of these animals decayed, the bones and teeth were well preserved.
The largest known deposits of fossilized dinosaur bones in the world are found in Dinosaur National Monument on the Colorado-Utah border in the United States. Dinosaur fossils have also been found in Germany, Belgium, and East Africa. The fossil remains of early humans have been found in the Great Rift Valley of East Africa.The data recorded in fossils is known as a fossil record. It is the primary source of information about the history of life on Earth. It dates life on Earth to more than a billion years. There are only a few fossil records for the early years. However, over the past 500 million years, many plant and animal remains have been preserved.Fossils may provide information about the climate, environment, plant life, and animal life of the site where they were deposited and preserved. The science of fossils is called paleontology. By studying fossils, scientists have proven that the Rocky Mountains, the Alps, and the Himalayas were once below the level of the ocean. Scientists know this because the remains of sea animals have been found high up on their slopes. Fossils have taught the scientists that the ancestors of the camel once roamed the plains of North America. They have also shown that tropical forests once covered the United States and Europe and that many plants once grew in the polar regions.
