B14 Genetics and Evolution

Question 1

How is the fossil formed?

Answer 1

1. When decay cannot happen

Question 2

How is the fossil formed?

Answer 2

2. When hard parts become ‘mineralised’

Question 3

How is the fossil formed?

Answer 3

3. When impressions/traces are left behind

Question 4

Outline of the process (1)

Answer 4

• happens when one or more of the conditions needed for decay are not there.
• this may be because there is little or no oxygen present.
• or poisonous gases kill off the bacteria that cause decay.
• sometimes the temperature is too low for decay to take place
• then the animals and plants are preserved e.g in ice or peat.

Question 5

Outline of the process (2)

Answer 5

• many fossils are formed when harder parts of the animal or plant are replace by minerals as they decay and become part of the rock.
• this takes place over long periods.
• mould fossils are formed when an impression of an organism is made in mud and then becomes fossilised, while cast fossils are made when a mould is filled in.
• rock fossils are the most common form of fossils.

Question 6

Outline of the process (3)

Answer 6

• some of the fossils found are not of actual animals or plants, but are preserved traces they have left behind.
• fossil footprints, burrows , rootlet traces (evidence of roots), and droppings are all formed.
• these help us to build up a picture of life on Earth long ago.

Question 7

Why is the fossil record incomplete?

Answer 7

The fossil record is incomplete because the original life forms were soft-bodied (like worms) and had no skeleton. Therefore they had no bones in their body. Fossils are formed from bones and if there is no bones, there would be no fossil. Most organisms that died did not become fossilised - the right conditions for the fossil formation were rare. Finally, there are many fossils that are still to be found.

Question 8

Evidence for evolution

Answer 8

Fossils provide evidence for evolution because the fossil record shows:

• how organisms have changed over time, including what are called ‘transitional forms’.
• a sequence of organisms over time (the order they appear in the rocks).

Question 9

The causes of extinction

Answer 9

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