Fossils are as remains, impressions, or traces of once-living organisms that are preserved in the earth's layers of rock. Organisms could be any type of plant or animal. Some examples of remains would be bones or hair. Dinosaur footprints, leaf prints, and old snail shells are all examples of fossils. The term comes from the Latin word, fossils, which is used to describe anything dug up from the ground.

Paleontologists are scientists who study fossils. Their work helps us know more about our history here on Earth. It can even give us clues about prehistoric times! By examining fossils, paleontologists can attempt to reconstruct past environments and identify the animals and plants that lived in them.

Fossilization

• Hard Parts: Petrified Fossils - Some fossils, such as bones, shells, or wood, are made up of the actual animal or plant that has died. The hard parts of the organism may remain intact over time. Fossils with hard parts are usually petrified, or turned into stone.
• Soft Parts: Exceptional Fossils - The soft parts of a plant or animal, however, are much more difficult to remain intact. Usually, they decompose. However, there are some ways that they can be preserved:

  Glacial Ice - Entire Woolly Mammoths from 40,000 years ago have been found in Siberia! Amber - Insects or other fossils can be preserved in amber, the hardened resin of certain type of trees. Tar Pits - More than 565 species of plants and animals are represented in the fossils of the Rancho La Brea Tar Pitt. But they aren't actually preserved in tar, it's actually asphalt!! Dehydration - Some of the oldest fossils are 150 million-year- old dehydrated dinosaur skin.

  Image courtesy of Steve Kurth. Fossils of New Jersey.

  Replacement fossils occur when the original bone or shell is slowly replaced by minerals in the ground.

Trace fossils are just made up of something the organism left behind. A leaf, for example, could leave an impression in the soil. After the leaf is gone, its print may remain in the soil, which hardens, making the print permanent.

A shell may leave an imprint from its inside or its outside. If soil enters the shell and an impression is made of its inside and it dissolves away, it could leave an internal mold. If the impression left is on the outside, it is an external mold. Sometimes, after the shell or other organism has dissolved away, soil and sediment will fill in where it used to be in the mold, creating a cast.

Different kinds of fossils can tell us different kinds of information. Coprolite fossils are droppings of an organism. These are important because they indicate the diet of the organism that secreted the dung. Footprints indicate an animals weight and how they moved from one place to the next. Borings and tunnels are the earliest evidences of life on land.

One way to tell the age of a fossil is to determine the time period from which the surrounding sedimentary rock is. Another way is to use radiometric dating.

Information about plants and animals also tells us about the past climate. Colonial corals found in the rocks of Greenland indicate that the country is much colder than it was long ago.