Biology- Fossils and Speciation

Fossils are remains of organisms from many years ago, which are found in rocks.

THREE WAYS FOSSILS ARE FORMED
1) Gradual replacement by minerals- things like teeth and bones don't decay and are replaced by minerals forming a rock-like substance

2) Casts and impressions- an organism is buried in soft clay and the clay hardens as the organism decays leaving a cast

3) Preservation- organsims can't decay in amber and tar as there is no oxygen or moisture.

Fossils show how today's species have evolved over millions of years.

SPECIES BECOME EXTINCT BECAUSE...

Environment changes too quickly, a new predator kils them all, a new disease kills them all, and they can't compete with other species for food.

Speciation- development of a new species

Speciation occurs when populations of the same species become so different that they can no longer breed together to produce fertile offspring.

ISOLATION= where populations of a species are seperated

• Isolation can happe due to a physical barrier (such as a flood/earthquake.)
• Conditions on either side of the barrier will be slightly different because the environment is slighty different on each side, different characteristics will become more common in each population due to natural selection.
• Eventually individuals from the different populations will have changed so much that they won't be able to breed with one another to produce fertile offspring.
• This group will become two seperate species.

Isolation and Natural Selection lead to Speciation