Fossils

Deep beneath one's own backyard may be the remains of plants and animals unlike any alive today. In many areas of the United States, if one digs long enough and deep enough, one may come across some ancient clamshells, a fragment of a big bone, a piece of petrified wood, or a leaf print.

Such relics are fossils. The term comes from a Latin word meaning “to dig,” for fossils are usually found by digging. They may be uncovered in the excavations for the foundation of a building, in stone quarries and coal mines, and in road cuts.

Kinds of Fossils

Fossils are remains of ancient life. There are many different kinds, because countless animals and plants lived in the past and they were preserved in many different ways. Sometimes the actual bone or tooth of an extinct animal was preserved in hot, dry locations. In moist places the original bone material was replaced, cell by cell, with minerals. It thus became fossilized, or petrified. If the once-living thing was a tree, the fossil may be a part of the tree trunk which underwent replacement of woody material with minerals
The fossil may be what is called a stone core. The shell of an ancient snail, for example, filled with fine sand after the animal died. Eventually the shell itself disintegrated, but meanwhile the sand that filled it had turned to stone. The stone exactly reproduced the inner shape of the shell. Sometimes the body of an animal was buried. It decayed and left a hollow mold which filled up with mineral matter, forming a cast of the animal's shape.
The fossil may be simply a print. The footprint of a prehistoric animal may have been preserved under layers of sand or silt. Prints are known of fishes, of butterflylike insects, and even of jellyfish. The delicate imprint of a leaf or blossom on some soft material may have later hardened into solid rock. Many different kinds of plants left leaf prints.
Another kind of fossil is called an inclusion. The object is usually small—an insect or a small piece of a plant, such as a blossom. It became embedded in the flowing resin of a pinelike tree. The resin fossilized into amber, and the embedded insect became a fossil too.
Animals which became trapped in tar pits are a variety of inclusion fossils. Rancho La Brea, in Los Angeles, Calif., is the most spectacular fossil area in the United States. Its sticky pools of oil and asphalt trapped thousands of prehistoric animals, much as flypaper catches flies. Saber-toothed tigers, giant wolves, sloths, mastodons, short-faced bears, and horses have been uncovered here. The flesh decayed and became part of the tar, but the bones and teeth were well preserved.
Finally, there are pseudofossils, or false fossils. These are mineral forms that look like fossils. If two pieces of slate do not quite touch for some reason and mineral-bearing water enters the crack, the minerals may be deposited to look like fossil moss or fossil ferns. Such pseudofossils are called dendrites, from the Greek dendron, meaning “tree.”

How Fossils Originated

The record of life on Earth goes back more than a billion years. The early part of the record is extremely scanty and difficult to read. Over the past 500 million years, however, starting in the Cambrian era of the Earth's history, many plant and animal remains have been preserved. From these remains the evolutionary history of life has been worked out . It is amazing that so much has been discovered, when one considers how very remote are the possibilities that even fossilized material could survive through such enormous periods of time.
Most animal fossils are those of creatures that died an accidental death in such a way that their bodies were quickly covered over. An animal that drowned near a river mouth and was swept out to sea and covered with sand and silt may have become fossilized. An animal that fell into a swamp or one that was covered by wind-blown sand during a storm in a desert and remained covered may be fossilized.
A special situation of fossilization occurred with the Siberian mammoths. These hairy elephants of the Pleistocene period occasionally fell into a crevasse of a glacier. Their bodies did not decay but were well preserved in the ice. These bodies remained in a subfossil state, meaning that they did not undergo the changes to make them fossils. It is known that wolves and huskies ate the flesh of such mammoths after they had thawed out.

Famous Fossil Sites

Several places in the world at one time offered the conditions for fossilization. Those in Europe were found first. Near Krems, in Austria, is a site famous for mammoth bones and animals associated with the mammoth such as the woolly rhinoceros.
Germany has two well-known sites. The quarries of Holzmaden, in Württemberg, furnished hundreds of skeletons of the marine reptile Ichthyosaurus. The quarry of Solnhofen, in Bavaria, yielded the remains of the earliest known bird, the archaeopteryx. Near Bernissart, in Belgium, were found skeletons of the dinosaur Iguanodon. Dinosaurs have also been uncovered at Tendaguru, in East Africa. Africa was also the home of ancient mammals, including early man.
In 1959 Louis S.B. Leakey found the remains— possibly 1³/₄ million years old—of an australopithecine, an apelike forebear of human beings, in Tanzania. In 1963 he announced the discovery of an enormous bed of animal bones 12 to 14 million years old at Fort Ternan, Kenya. Here, and also in Olduvai Gorge, in Tanzania, he found extinct forms that gave rise to the modern giraffe, elephant, rhinoceros, antelope, ostrich, and others.
Sites elsewhere in Africa have yielded remains of very early hominids, ancestors of modern humans. In Ethiopia and Tanzania, for example, the earliest known hominid species are represented by the famous incomplete skeleton “Lucy” from Ethiopia dates back at least 3 million years. The skeletal remains and fossilized footprints of these hominids show that they walked upright.
In the United States are the largest known deposits of fossilized dinosaur bones in the world, in Dinosaur National Monument, on the Colorado-Utah border . The tar pits of Rancho La Brea, in Los Angeles, and the Atlantosaurus beds of Wyoming have also yielded dinosaur fossils. Near Kayenta, Ariz., in 1953, Tritylodon skeletons were found “weathering out” of the sandstone rocks. The Tritylodons were mammallike reptiles which lived some 175 million years ago.

How Fossils Are Handled

Fossil hunters should have some knowledge of geology in order to recognize the kinds of places in which fossils are likely to be found. Undisturbed sedimentary deposits are among the best possibilities. These are exposed in coal mines, road cuts, and sandstone and limestone quarries. A marble quarry would be worthless because marble is a metamorphic rock formed under conditions that would destroy any fossils in the original rock.
Once a fossil has been discovered, the first task is to remove it from the site. No attempt is made at the site to remove the fossil from the matrix, as the stone in which it is embedded is called. Instead, a piece of rock large enough to be sure that it contains the whole fossil is chiseled out. Fossils found in the mud of a river bed or in loose sand may be washed on the spot.
If the fossil site is large, it may have to be cut up with a stone saw. This requires professional skills. In addition, permission must be obtained from the owner of the site. Professionals photograph the whole site before starting to work. The pieces are numbered as they are cut out, so that they can be put together exactly as they were found.
Sometimes a fossil that has weathered out of the rock has become soft and crumbly in the weathering process. In that case a different procedure is followed. Burlap is soaked with wet plaster of Paris and wrapped around the exposed end of the bone. Then the block of stone is cut out, and the whole is wrapped in more burlap soaked in plaster of Paris before it is crated for shipment. If the fossil is something that might be damaged if it is moved, such as a footprint or a leaf print, plaster casts are made on the spot.
The most difficult process is freeing the fossil from the matrix. The instruments used are the sculptor's chisel for the rough work and engraving tools and dental drills for the fine work. Whoever undertakes this work must know the particular kind of extinct animal on which he is working. He must know where every bone is supposed to be. He must also be able to guess where the bones might be if the fossil has been squeezed out of shape by the weight of the rock.
After the fossils have been freed from their matrix they must be carefully preserved. Glue is applied to the cracks, and the surface then is covered with shellac or with hot paraffin.

What Fossils Teach

The science of fossils is called paleontology, from Greek words meaning the science (logia) of very old (palaios) existing things (onta). The science of extinct animals is paleozoology. The science of extinct plants is paleobotany. The science that tries to establish the climate of the past from the fossils of a given locality is paleoclimatology. The science that tries to trace ancient geographical features is paleogeography.
By studying fossils, scientists have been able to piece together some of the important pages in the history of the Earth and its people. They have proved that the Rocky Mountains, the Alps, and the Himalayas were once below the level of the ocean, for the remains of sea animals have been found high up on their slopes. From fossils scientists have learned also that the ancestors of the camel once roamed the plains of North America; that tropical forests once covered the United States and Europe; and that many plants once grew in the polar regions.
Fossils show that the great coal and chalk beds of the world were formed from the remains of living things. Millions of years ago tiny animals were making shells that became the limestone of today.
Fitting together the scattered parts of the fossil story, science has traced animal life back to the earliest worms and shellfish. It has shown how, one after another, there appeared cartilaginous fishes, amphibians (half-land, half-water animals such as the frog), insects, reptiles, birds and bony fishes, and mammals.
Strangest of all creatures are the giant monsters of the Era of Reptiles—the dinosaurs, the ichthyosaurs, and other scaled, horny creatures of dragonlike appearance . Some of these old reptiles were about 100 feet (30 meters) long—the largest land animals that ever lived. Those who study fossils learn from these remains that the farther back in time an animal lived, the smaller is the proportion of brain space in its skull. Hundreds of species of great size and strength died out and made way for creatures with more brain and less bulk. The latest of all fossil remains are those of early humans found mostly in the Great Rift Valley of East Africa.