IB Fossils © Oxford University Press 2011 Fossils

IB Fossils © Oxford University Press 2011 Evidence for evolution  Fossils are the preserved remains of living things from many years ago.  They are the most significant evidence to support the idea of evolution by revealing the gradual change of one type of plant or animal into another over time.

IB Fossils © Oxford University Press 2011 How are fossils formed? Perhaps the best known fossils are those found in rock, formed as the hard parts of the organism are replaced by minerals. These fossils are formed like this: 1.The plant or animal dies, and falls into soft mud or silt, often at the bottom of a lake. 2.The body becomes covered in silt or mud. 3.The silt or mud gradually turns to rock, encasing the dead body. 4.Over millions of years the hard parts of the body of the plant (leaves) or animal (bones and shells) become replaced by minerals. 5.Soft parts of bodies do not fossilise well because they decay quickly. 6.If earth movements make the land rise, then the remains may become exposed at the surface.