fossils are skeleton or parts of skeletons or leaf or animal imprints embedded in and preserved
in the Earth’s crust.
The study of fossils across geological time, how they are formed and how they have evolved
in relation to other phylogenetic groups is calledpalaeontology.
How fossils are formed
- For fossilisation to occur a plant or animal must first die. Soft tissues decay quite
quickly, therefore animals that have hard exoskeletons and woody plants tend to fos-
silise better than soft-bodied organisms. - The organism (plant or animal) must be buried beneath mud and or soil shortly after
death. Although decay still takes place, the lack of oxygen slows it down. As more and
more layers of mud and soil are added, the sediments become compressed. - Eventually this compression turns the sediment into rock, which forms a mould around
the shape of the original skeleton. Sometimes the original bone or shell softens and dis-
solves completely, sometimes the bone or shell remains. Water that is rich in dissolved
minerals trickles in through the layers of sediment into the mould.
Chapter 11. History of Life on Earth 319