Fossils

Fossils

• Fossils are the remains of organisms from many thousands of years ago, which are found in rocks. They provide the evidence that organisms lived ages ago. Fossils can tell us a lot about how much or how little organisms have changed (evolved) over time. 
• Fossils can form from gradual replacement by minerals. Things like teeth, bones, shells etc, whch do not decay easily, can last a long time once buried. They're eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part. The surrounding sediments also turn to rock and eventually someone digs it up.
• Fossils can also form from casts and impressions. Sometimes, fossils are formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays, leaving a cast of itself. An animal's burrow or a plant's roots (rootlet…