Fossils form in different ways s2901/es2901page01.cfm?chapter_no=visualization Hard parts that do not decay easily such as teeth and bones. Whole organism preserved in ice. Hard parts of an organism get replaced by other minerals.. …most common. Traces of plants or animals are left behind.

Why do some organisms die out completely? Living things themselves can cause the extinction of each other. New predators to an environment. The Brown Tree Snake was taken from Australia to Guam after WWII. It caused extinction of many bird species.

New diseases (microorganisms). A highly infectious cancer is killing many Tasmanian Devils. Extinction on islands are common where animals live closely together. This disease is spread easily, attacks and kills them quickly.

Competition between species and mutations that give one species an advantage over another. 24 European rabbits were released into the wild in Australia by an Englishman, Thomas Austin. They bred so fast and ate so much that they quickly took over. Native animals died out quickly.

Summary New predators New diseases Competition or mutations that give an advantage to one species over another. Remember many other things can cause CHANGES… a current problem is CLIMATE CHANGE

North Uist Hedgehogs introduced to solve the problem of slugs. Hedgehogs bred rapidly. They began eating eggs and chicks of rare sea birds. Who will become extinct? EXAM TIP! If you give a reason for an extinction… tell the examiner what change caused it!

Why are fossils useful? Why are fossils useful? They give us information and evidence about organisms that lived millions of years ago. Most scientists now believe the Earth is 3 to 4 billion years old. Incomplete fossil record is a problem. Rocks are constantly melting and moving. Have we found all the fossils out there?

Some evidence… Fossil records of the horse is good evidence for how this animal has changed over 55 million years.

Eohippus had 4 toes and lived on swampy ground 55 million years ago!

Problems with the fossil record. Incomplete record. Not enough fossils to show intermediate species existed. Soft bodied organisms. Rock cycle.

A wonderfully celebrated fossil! Archaeopteryx Thought to have lived 150 million years ago Unearthed 1860/1 in Germany. Other specimens have since been found.