Topic 6 - Fossils

Question 1

Give two examples of organism traces that can be preserved as casts and impressions.

Answer 1

Footprints.

Rootlet traces.

Question 2

Why didn’t many of the earliest forms of life form fossils. (2 marks)

Answer 2

The majority of early life was soft bodied animals.

They have soft tissue which generally tends to decay away.

Question 3

What are soft bodied animals?

Answer 3

Animals that lack skeletons and have soft tissues.

Question 4

Why are so little fossils present today? (2 marks)

Answer 4

Most of them were destroyed by geographical activity.

One such example is tectonic movement.

Question 5

Explain how casts and impressions are formed. (4 marks)

Answer 5

The organism is buried underground in soft material such as clay.
The clay hardens and the organism decays.
This leaves behind casts of itself.
Animals can also step onto soft material leaving an impression.

Question 6

Explain the process of mineral replacement. (3 marks)

Answer 6

Decay resistant materials take longer to decay.
Minerals eventually replace the material to form a rock like substance shaped like the original bone.
The surrounding sediment also turns to rock.

Question 7

Explain the process of preservation. (4 marks)

Answer 7

Insects get trapped in amber and tar pits.
There is no oxygen or moisture so microbes can not decay the insects.
In glaciers, it is too cold for microbes to decay insects.
Insects can also be preserved in peat bogs as it is too acidic for microbes to survive.