B14- Genetics And Evolution

Question 1

How are fossils formed when the animal does not decay

Answer 1

When an animal or plant does not decay after it has died. This happens when one or more of the conditions needed for decay are not there. For example
-little or no oxygen present
-poisonous gases kill of the bacteria that cause decay
-temperature too low
The animals are then preserved almost intact

Question 2

How are animal traces fossilised

Answer 2

Some fossils found are not of actual animals or plants but are preserved traces they have left behind. For example fossil footprints, burrows , rootlet traces and droppings are all formed

Question 3

How are fossils formed when the harder parts are replaced by minerals

Answer 3

Many fossils are formed when harder parts of the animal or plant are replaced by minerals as they decay and become part rock. Mould fossils are formed when an impression of an organism is made in mud and then becomes fossilised

Question 4

Three reasons why the fossil record is incomplete

Answer 4

Many of the earliest forms of life were soft bodied organisms, they have left little fossil trace.
The majority of any fossils that were formed in the earliest days will have been destroyed by geological activity including the formation of mountain ranges, continental movements, erosion, volcanoes and earthquakes.
Most organisms that died did not become fossilised - the right conditions for fossil formation were rare
Finally there are many fossils still to be found