Topic 6 - Fossils

Question 1

How can fossils form from gradual replacement by minerals?

Answer 1

1) Teeth, bones, shells don’t decay easily and so take long to decay when buried
2) They are eventually replaced by minerals forming a rock like substance shaped like the original hard part
3) Surrounding sediment also turns to rock but fossil stays distinct

Question 2

In what ways can fossils form?

Answer 2

• Gradual replacement by minerals
• From casts and impressions
• From preservation in places where no decay happens

Question 3

How can fossils form from casts and impressions?

Answer 3

1) Sometimes fossils form when an organism is buried in a soft material like clay
2) The clay hardens around it as it decays leaving a cast

1) Things such as footprints can also be pressed into soft materials leaving impressions when they harden

Question 4

How can fossils form from preservation?

Answer 4

1) In amber and tar pits there is no oxygen or moisture so decay organisms can’t survive
2) In glaciers it is too cold for them to work
3) Pete bogs are too acidic for decay microbes

Question 5

Why is there a lack of evidence for where life began?

Answer 5

• Many early forms of life were soft-bodied, and soft tissue tends to decay completely
• Fossils formed millions of years ago were destroyed by geological activity