What Fossils Tell Us

What fossils tell us
This chapter looks at fossils and their formation. Fossils are traces of ancient plants or animals preserved in rocks. The number of fossils and their placement in rocks is called the fossil record. The study of fossils is called palaeontology.
Because fossils are buried in rock, most of the time they are found only when the rock is dug up, worn out or cut away. Fossils may include parts of animals, their footprints, eggs or nests. Plants and their spores, or seeds, also make up part of the fossil record. Most ancient animals and plants did not leave any fossils so we will never know of their existence.
Types of fossils
There are several types of fossils: mould fossils - a fossilised impression in the rock or a negative
A quick burial is most likely to happen near the water which makes the fossils of sea creatures the most common. Fossils of land animals are quite rare. Usually all that remain to tell us what the creature looked like are just the hard parts like the shell, bones and teeth. That is why sometimes it is impossible to find out if that creature had fur, what colour it was, or what size its body parts were.
Here are the main steps in fossil formation:
Animals are quickly buried after their death by sinking in mud or sand.
Over time, more and more rocks and various sediments cover the remains.
Parts of the animal or the entire animal that do not rot are covered by new sediments.
Some parts of the dead animal (that do rot or get eaten by other animals) turn into fossils over time.
After long periods of time, the chemicals in the buried animal's body change. As the animal's bone slowly rots, water seeps into the bone and replaces the bone (organic) chemicals with other rock-like (non-organic)
Some chemical elements can turn into different elements over time. They are called radioactive chemical elements and their change into different elements is called radioactive decay. Radioactive elements are natural parts of rocks and they decay at a known rate. The original element, called 'parent', gradually decays into 'daughter' elements. This process is irreversible. By measuring the parent and daughter elements in a given rock (knowing the decay rate) it is possible to calculate the time passed from the fossil's formation.The fossil's age equals the age of rocks in which it is