Fossils
Fossils are remains of old animals and plants that lived a long time ago. They help scientists figure out the history of Earth. Fossils can help tell what extinct plants and animals looked like, how the continents were formed, and even tell us about the climate. Fossils don't have to be whole plants and animals preserved, they can be just parts, like just a bone or just a leaf. There are different categories of fossils, such as petrified fossils, molds, casts, imprints, and trace fossils. Petrified fossils are parts of the organism, like bones, shells, or tree trunks, that still look like themselves, but are actually rock, because minerals replace the hard parts. Most of dinosaur bones are petrified fossils. Molds are hollowed out spaces in rocks that mimmic the shape of the organism that was in the rock before it dissolved. Casts are the solid forms of organisms that are created when the mold fills up with a sediment. Trace fossils show movement made by organisms in the rock, like footprints, trails, or burrows. Imprints are impressions of parts of living things left in mud or sand before it hardens, thin objects like leaves or feathers. Not everything living gets fossilized because there are so many chances for a once living organism to e destroyed. If left lying on the surface, they can be attacked by bacteria, and bones and shells can be crushed or be eroded along a seashore or stream bed. Organisms that have hard body parts, or is covered in a sediment shortly after death, it has a better chance of being preserved.
PICTURES
Fossil of shells in a rock
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Fossil of a Trilobite