Evidence for Evolution

• Fossils are remains of organisms from millions of years ago, preserved in the rocks.
• A replacement fossil is a gradual replacement by minerals. Things that don't decay easily can last a long time. Eventually, they are replaced by minerals as they decay. The fossils stay distinct inside the rock.
• Cast and impression fossils happen when an organism is buried in a soft material like clay. It later hardens against the organism, leaving a cast of itself. An animal's burrow or plant's rootless traces can be preserved as casts.
• Preservation happens in places where no decay occurs.
• To decay, decomposers need oxygen, enough moisture, optimum temperature and pH, so decay won't take place.