Fossils are preserved remains or traces of dead organisms which are found in rocks.
Fossils can be formed from:
- Hard body parts, such as bones and shells, which do not easily or are replaced by other materials as they decay
- Parts of animals which have not decayed. For example dead animals can be preserced in amber, peat bogs, tar pits or in ice.
- Casts or impressions, such as foot prints or burrows.
The Fossil Record
Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms are found in the newest rocks.
This supports the theory of evolution, which states that simple life forms have gradually evolved into more complex ones.
Although many early forms of life where soft bodied, which means they have left few traces behind. We can learn from fossils how much or little different organisms have changed
Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its environment will not survive and will become extinct.
Extinction may be caused by:
- New diseases
- New predators
- New, more successful competitors
- Changes to the environment over geological time - such as change in climate
- A single catastrophic event - such as volcanos ect.
New species can arise as a result of:
Isolation - Two populations of a species become seperated e.g. geographically.
Genetic Variation - Each population has a wide range of alleles that control their characteristics
Natural Selection - In each population, the alleles that control the characteristics which help the organims to survive are selected
Speciation - The populations become so different that sucessful interbreeding is no longer ppossible.