What Is Fossil Evidence?

Taphonomy

• Taphonomy is the study of how fossils form. Fossils are preserved in sedimentary rock, the most plentiful type of rock found in Earth's crust. Fossils form when the remains of living things become buried in layers of sedimentary rock. Most fossils are made from the hard parts of an organism, such as bones, teeth or shells. Soft tissues are very rarely preserved. Bacteria consume the organic parts of bones and the spaces that remain fill with water or sediment. Over time, bones become mineralized and preserved as rock-like fossils.

Age of Fossils

• Sedimentary rocks form when rock particles stack together in layers. The principle of superposition states that the layers are sequential. More layers accumulate as time passes; older layers lie below younger layers. Scientists look at the fossils found in each layer to help determine the age of the rocks. If the age of a rock layer is known, scientists can use that information to date new fossils found there. Scientists determined that fossils found in a rock layer of one age are absent from rock layers of different ages. Therefore, fossils found in layers of rock of the same age come from the same time period.

Species Change

• The fossil record provides evidence for the changes a species experiences over time. Members of a species share physical characteristics that they pass on to their offspring. The physical characteristics of living things preserved in fossils help scientists determine how ancient organisms were related and how they relate to contemporary species. Paleontologists can classify fossils of organisms in the same species if they share the same degree of similarity as individuals in a living species.

What Fossils Tell Us

• Fossil evidence documents the extinction of species and the rise of new species. The fossil record also shows how groups of organisms evolved by the acquisition or disappearance of physical characteristics. The fossil record presents pieces of evidence like pieces of a puzzle. When enough pieces come together, the puzzle begins to take shape and becomes clearer. Each new fossil found contributes to the body of evidence for the process of evolution by providing a missing link between groups of organisms, supporting the evidence that has already been gathered or disproving old ideas and introducing new ones.