Fossils reveal much about Earth's past events.
Fossilized remains help scientists determine the record of events throughout history. Fossils tell the story of life on Earth. Fossils are remains of living things. The soft parts of living things easily decompose; the hard parts are usually preserved. By studying the fossil record in layers of sedimentary rock, scientists are able to develop a picture of how life developed over time. Fossils reveal population explosions. They help scientists pinpoint climate change events. They offer insight into extinctions.
The Evolutionary Story
Scientists use fossils to show how living things change over time. They look at shared features in fossils, and group these organisms together. For example, they group together all fossils with vertebrae and brains, and under that group they create a subgroup that is all animals with four legs. Scientists use fossils for comparisons. When two similar species are found, this gives insight into the evolutionary story of these organisms. The sum of fossils is called the fossil record. With this record, the relationships between current living things and ancient ones are shown.
Index Fossils
The fossils of some organisms are easy to identify. These same fossils are found worldwide, indicating that these organisms lived over a large geographic area. It is especially useful when an organism existed for a short amount of geological time relative to the amount of time living things have existed. The fossilized remains of these special organisms are called index fossils and they serve as time markers. When an index fossil is found in a layer of sedimentary rock and scientists find a new fossil in that same layer, they are able to determine the relative time this new organism lived because of proximity.
The Cambrian Explosion
The fossil record reveals surprises. Evolution can move forward rapidly. Fossils are used to tell the story of the Cambrian explosion that began 545 million years ago. At this time, a huge number of complex organisms appeared on Earth. The size of animals also radically changed from smaller to much larger organisms. Fossils are used to show this explosion. The fossil record reveals that in a relatively short period of geological time -- 10 million years -- a foundation formed for the most complex living things found on Earth now.
Extinction
Suddenly and with no reason, mass numbers of organisms disappear from the fossil record. Fossils are used to track extinction events in the history of Earth. Estimates indicate that 99 percent of all species that have lived on Earth are extinct. The most studied and famous extinct animals are the dinosaurs. Fossils are used to document extinction patterns. The fossil record show Earth recovers very slowly from an extinction event. Currently, Earth's living organisms are becoming extinct at a fast rate. The fossil record helps scientists predict what this mass extinction will mean for Earth in the future.
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