A fossil is the preserved remains or impressions of a living organism such as plant, animal, or insect. Some fossils are very old. Fossil help scientists to learn about the past history of life on Earth. They are found all over the world. Most fossil are found in sedimentary rock such as shale, limestone, and sandstone.
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How do fossils form?
There are a number of ways that fossils may form.
- Amber – Full body insect fossils can be found preserved in hardened tree sap called amber. These fossil can remain preserved in amber for up to millions of years.
- Carbonization – Carbonization is when all the elements of the organism are dissolved except for the carbon. The carbon leaves a residue which shows an outline of the organism.
- Casts and molds – A cast or a mold fossil is an impression of a living organism. They are made when an organism dissolves in the Earth and leaves a hollow mold behind. The mold is then filled in by minerals leaving something like a statue of the organism behind.
- Freezing – Some fossil are preserved in ice. As long as the ice doesn’t melt the fossil may be preserved for thousands of years. Large fossil such as the wooly mammoth have been discovered in the glaciers of the Arctic.
- Mummification – In really dry areas a fossil may be formed through mummification. This is when the dead organism quickly dries out. Because there is little moisture, the remains of the organism can be preserved for a long time leaving a fossil.
- Permineralization – Permineralization is when a mineral deposits form a cast of the organism. Fossils formed this way can be very detailed. Common minerals include silicate, carbonate, and pyrite.
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Types of Fossils
There are two main types of fossil: body and trace fossil.
- Body fossils – Body fossil are fossil where some portion of the actual organism’s body remains as part of the fossil. This might be a tooth or piece of bone.
- Trace fossils – Trace fossil are fossil where there isn’t any actual part of the original organism, but “traces” of the organism are preserved in rocks and minerals. There are many different types of trace fossils including molds, animal tracks, casts, and impressions.
Interesting Facts about Fossils
- The word “fossil” comes from the Latin word “fossilis” meaning “obtained by digging.”
- When a geological process produces a pattern that looks like a fossil but isn’t really, it is called a pseudo-fossil.
- Paleontologists are scientists that study prehistoric life by studying fossils.
- The skeletons of dinosaurs have been recreated using fossilized bones found in the earth.
- Scientists can use dinosaur footprints to determine the speed the dinosaur ran, the number of legs it had, and if the dinosaur traveled in groups.
- Fossil of rocks called gastroliths have been found. These rocks were swallowed by dinosaurs to help them digest their food.
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