What is a fossil?

Dinosaur Fossil
A Dinosaur Fossil

A fossil is an object from millions of years ago which has been preserved in rock.

Most fossils are of bones or teeth because these hard objects are preserved more easily than soft skin or muscles.

Over millions of years, the original objects rot away and are replaced by minerals from the surrounding rocks.

The fossils can be very heavy and are often fragile as well.  Sometimes rare fossils of skin or muscles are found.