Fossils

Question 1

Define fossils

Answer 1

Fossils are the remains or impressions of dead animals and plants from millions of years ago, which are found in sedimentary rocks.

Question 2

What environment is needed to the formation of fossils?

Answer 2

• No bacteria
• Lack of oxygen
• Low temperature
  This prevents decay, and this is important for fossils to form properly

Question 3

Describe fossilisation by mineralisation

Answer 3

Most fossils occur through mineralisation:
1. Hard parts of the organisms like teeth, shells and bones don’t decay easily, and can last a long time when buried.
2. As they decay the fossils are replaced by minerals, forming a rock-like substance shaped like the original hard part.
3. The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock, and eventually someone digs it up.

Question 4

Describe fossilisation from casts and impressions

Answer 4

1. Sometimes fossils are formed when an organism is buried in a soft material such as clay. This can harden around the organism, and when the organism decays it leaves a cast of itself.
   An animal’s burrow or a plant’s roots can be preserved as casts.
   2.Things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens.

Question 5

Describe fossilisation from preservation in places where NO DECAY happens.
Which environments have low levels/ no decay?

Answer 5

1. In amber ( a clear yellow ‘stone’ made from fossilised resin/ tree sap) and tar pits there’s no moisture or oxygen so decay microbes are unable to survive.
2. In glaciers, it’s too cold for decay microbes to work.
3. Peat Bogs are too acidic for decay microbes.

In environments like these no decay can occur preserving both the soft and hard parts (the whole) of an organism.