Paleontology is the study of the history of life on Earth. It looks at fossils, which are the preserved remains of plants, animals, and other living things. Fossils are mainly formed in two ways. In one case, animal or plant matter is replaced by rock over time, but the remains still keep their original shape. In the other case, the fossil is an impression that has been preserved in rock. It can be a footprint, for example, or the outline of a body pressed into mud.

Paleontologists use fossil remains to better understand the way species evolve over time. They study both species that still exist and extinct ones that have long since died out.

Individual fossils can contain information about an animal or plant's life and environment. For example, each ring on the surface of an oyster shell represents one year of its life. Studying oyster fossils can help paleontologists discover how long the oyster lived and in what conditions. If the climate was favorable for the oyster, the oyster grew more quickly and the rings would be thicker. If the oyster struggled for survival, the rings would be thinner. Thinner rings suggest the environment was unfavorable for oysters and similar creatures. They suggest, for example, that the water was too warm or too cold for the oyster.

Some fossils provide information about many kinds of living things. Amber, for instance, is hardened, fossilized tree resin. As the sticky resin dripped down a tree trunk, it has sometimes trapped small insects and even things like frogs and lizards. Paleontologists study amber to observe these complete specimens. Amber can preserve tissue as delicate as dragonfly wings. It can also provide information about the way animals lived. For example, some ants were trapped in amber while eating leaves. Scientists were thus able to see exactly what the ants ate.

The behavior of organisms can also be deduced from fossil evidence. For instance, paleontologists believe duck-billed dinosaurs called hadrosaurs lived in large herds. They concluded this after observing a single site with around 10,000 hadrosaur skeletons.

Fossils can also provide evidence of the evolutionary history of organisms. For instance, paleontologists have concluded that whales evolved from land-dwelling animals. They reached this conclusion because fossils of extinct animals closely related to whales have front limbs like paddles, similar to front legs. They even have tiny back limbs. The front limbs of these fossil animals are in some ways similar to legs. However, they also show strong similarities to the fins of modern whales.

Subdisciplines of Paleontology

The field of paleontology has many subdisciplines. A subdiscipline is a narrower field of study within a broader subject or discipline.

Vertebrate Paleontology

One important subdiscipline is vertebrate paleontology, the study of fossils of animals with backbones. Vertebrate paleontologists have discovered and reconstructed the skeletons of dinosaurs and many other ancient animals. They have been able to show how these animals lived and evolved.

Take the example of pterosaurs, a group of flying reptiles. Using fossil evidence, vertebrate paleontologists deduced that pterosaurs could fly by flapping their wings, as opposed to just gliding. Reconstructed skeletons of pterosaurs have hollow and light bones like modern birds. One type of pterosaur, Quetzalcoatlus, was one of the largest flying creatures in history. It had an 11-meter (36-foot) wingspan.

Invertebrate Paleontology

Invertebrate paleontologists examine the fossils of animals without backbones. Mollusks, corals, crabs, shrimp, sponges, and worms are all examples of invertebrates. Unlike vertebrates, invertebrates do not have bones. However, they do leave behind evidence of their existence. This evidence includes fossilized shells, impressions of soft body parts, and tracks along the ground or ocean floor.

Invertebrate fossils are especially important to the study of past environments. For example, large communities of 200-million-year-old invertebrate marine fossils have been found in the deserts of Nevada, in the United States. They tell us that parts of the state were once covered by water.

Paleobotany

Paleobotanists study the fossils of ancient plants. These fossils can be impressions of plants left on rock surfaces. Or, they could be parts of the plants themselves that have been preserved by rock material. Such fossils help us understand the evolution of plants. They also play a key part in helping scientists understand what ancient environments were like.

Micropaleontology

Micropaleontology is the study of fossils of tiny microscopic organisms. Micropaleontologists use powerful microscopes to study microfossils that are generally smaller than four millimeters (0.16 inches).

Micropaleontologists often study fossils to better understand how Earth's climate has changed. For example, many study shells from deep-sea microorganisms. Such creatures draw the elements for their shells from the ocean water around them. Thus, the composition of the shells reflects the composition of the ocean during the creatures' lifetime. In turn, the chemical composition of the ocean provides many important clues about what the climate must have been like. By studying shells from different periods, micropaleontologists can learn how the ocean and the climate changed over time.

History of Paleontology

Throughout history, people have uncovered fossils, but they did not always understand what they were or where they came from. Modern paleontology first developed in the 1700s. At that point, scientists began to carefully study and classify fossils for the first time.

In the 1850s, scientist Charles Darwin suggested that new species evolve over time. Over thousands or millions of years, one species can develop into another, Darwin said. Creatures living today are related to species from the distant past, as different as they may seem from one another.

After accepting Darwin's theory of evolution, paleontologists began drawing connections between ancient fossils and living creatures. The prehistoric Archaeopteryx, for example, had wings like a bird. Yet, it had teeth and other features typical of a type of dinosaur called a theropod. That led paleontologists to conclude that the Archaeopteryx was a very early kind of bird. It was one of the first steps in the path from ancient dinosaurs to modern birds.

In the late 1800s, scientists discovered radioactivity. Radioactive objects send out a certain amount of energy over time. Scientist use a special process, called radiometric dating, to find out how old fossils are. By measuring radioactive material in an ancient sample and comparing it to a current sample, scientists can calculate how much time has passed. This tells them how old the fossil is.

Paleontology Today

Modern paleontologists use a variety of advanced tools. Electron microscopes allow them to study the tiniest details of the smallest fossils. X-ray machines and CT scanners reveal fossils' internal structures. Advanced computer programs can reconstruct whole skeletons. They can show how extinct animals looked and moved.

Paleontologists still make important discoveries with simple tools. Around the world, many are digging away, hoping to shed new light on the evolution of life on Earth.