Fossils

- Teeth, sheels and bones don't decay easily so will last for a long time when buried

- They are eventually replaced by minerals as they decay, which forms a rock-like substance that is shaped like the original 

- The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock until someone digs it up

- Fossils can be formed when an organism is buried in a soft material like clay - the clay later hardens around it and the organism decays, which leaves behind a cast of itself

- An animals burrow or a plants roots can be preserved as casts

- Things like footprints can also be pressed into these soft materials, which leaves behind an impression when it hardens

- Amber is a clear, yellow stone made from fossilised resin

- In amber and tar pits, there is no oxygen or moisture so decay microbes can't survive

- In glaciers it is too cold for the decay microbes to work

- Peat bogs are too acidic for decay microbes

- Fossils provide evidence that organsims lived ages ago and they show how much or how little an organism has evolved over time - scientists are still unaware of where the first form of life came from - there are various hypotheses

- It is possible that the first life forms came into existence in a primordial swamp (under the sea) - it may also be that simple organic molecules were brought to earth on comets, which could have become more complex molecules and, eventually, very simple life forms

- Hypotheses can't be proved or disproved due to lack of good, valid evidence - many early life forms were soft bodied and soft tissue tends to decay away completely, so the fossil record is incomplete

- Fossils that did form millions of years ago may have been destroyed by geological activity