Paleontology is the study of the history of life on Earth. It focuses on fossils, which are the remains of plants, animals, and other living things that have been replaced by rock material or whose impressions have been preserved in rock. Paleontologists use fossil remains to understand different aspects of extinct and living organisms.
Individual fossils may contain information about an organism's life and environment. For example, each ring on the surface of an oyster shell denotes 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 probably grew more quickly and the rings would be thicker. If the oyster struggled for survival, the rings would be thinner. Thinner rings would indicate an environment not favorable to organisms like the oyster. They would suggest, for example, that the water was too warm or too cold for the oyster, or that it lacked the necessary nutrients.
Some fossils show how other organisms lived. Amber, for instance, is hardened, fossilized tree resin. As the sticky resin dripped down a tree trunk, it has sometimes trapped small insects and some organisms as large as frogs and lizards. Paleontologists study amber to observe these complete specimens. Amber can preserve tissue as delicate as dragonfly wings. Some ants were trapped in amber while eating leaves, allowing scientists to know exactly what they ate, and how they ate it.
The behavior of organisms can also be deduced from fossil evidence. For instance, paleontologists suggest that duck-billed dinosaurs called hadrosaurs lived in large herds. They reached this conclusion after observing a single site with approximately 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. Fossils of extinct animals closely related to whales have front limbs like paddles, similar to front legs. They even have tiny back limbs. Although the front limbs of these fossil animals are in some ways similar to legs, in other ways 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 specialized field of study within a broader subject or discipline. In the case of paleontology, subdisciplines can focus on a specific fossil type or a specific feature of Earth, such as its climate.
One important subdiscipline is vertebrate paleontology, the study of fossils of animals with backbones. Vertebrate paleontologists have discovered and reconstructed the skeletons of dinosaurs, turtles, cats, and many other animals. They have been able to show how these animals lived and what their evolutionary history was.
Using fossil evidence, vertebrate paleontologists deduced that pterosaurs, a group of flying reptiles, 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, is considered one of the largest flying creatures in history. It had an 11-meter (36-foot) wingspan.
Invertebrate paleontologists examine the fossils of animals without backbones. Mollusks, corals, crabs, shrimp, sponges, and worms are all examples of such creatures. Unlike vertebrates, invertebrates do not have bones. However, they do leave behind evidence of their existence. Such 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.
Paleobotanists study the fossils of ancient plants. These fossils can be impressions of plants left on rock surfaces. Or, they can be parts of the plants themselves—such as leaves or seeds—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 is the study of fossils of microscopic organisms. Micropaleontologists use powerful electron microscopes to study microfossils that are generally smaller than four millimeters (0.16 inches).
For example, micropaleontologists study shells from deep-sea microorganisms in order to understand how Earth's climate has changed. Shells build up on the ocean floor after the organisms die. Because the organisms draw the elements for their shells from the ocean water around them, the composition of the shells reflects the composition of the ocean during their lifetime. By chemically analyzing the shells, paleontologists can determine the amount of oxygen, carbon, and other life-sustaining nutrients in the ocean when the shells developed. They can then compare shells from different times to see how the ocean has changed. Differences in the chemical composition of the ocean can be good indicators of differences in climate.
History of Paleontology
Throughout human history, fossils have been used, studied, and understood in different ways. Early civilizations used fossils for decorative or religious purposes but did not always understand where they came from.
Some ancient Greek and Roman scientists did recognize that fossils were the remains of life forms. However, many early scholars believed fossils were evidence of mythological creatures such as dragons. During the Middle Ages, many people believed fossils were remains left behind by Noah's flood.
The formal science of paleontology began in the 1700s. For the first time, scientists began to carefully study and classify fossils. In the 1850s, scientist Charles Darwin suggested that new species evolve over time. New fossil evidence supported Darwin's theory of evolution.
Darwin's theory allowed paleontologists to study living organisms for clues to understanding fossil evidence. The prehistoric Archaeopteryx, for example, had wings like a bird. Yet, it had other features—such as teeth—typical of a type of dinosaur called a theropod. Now regarded as a very early bird, Archaeopteryx retains more similarities to theropods than does any modern bird.
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.
Modern paleontologists have a variety of tools that help them discover, examine and describe fossils. Electron microscopes allow paleontologists to study the tiniest details of the smallest fossils. X-ray machines and CT scanners reveal fossils' internal structures. Advanced computer programs can analyze fossil data and reconstruct skeletons. They can be used to visualize the bodies and movements of extinct organisms.
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.