Fossils and Extinction

Question 1

What are fossils?

Answer 1

The remains of organisms from many years ago, which are found in rocks. Fossils provide the evidence that organisms lived ages ago.

Question 2

In what 3 ways can fossils form?

Answer 2

1) Gradual replacement by minerals
2) Casts and Impressions
3) Preservation in places where no decay happens

Question 3

Things like [ ], [ ], bones etc. which don’t decay easily, can last a long time when buried

Answer 3

Teeth, shells

Question 4

Describe how mineral replacement works

Answer 4

Teeth, bones, shells etc. are eventually replaced with minerals as they decay forming rock-like substances shaped like the original hard part
The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock

Question 5

Describe the conditions where castings happen

Answer 5

When organisms are buried in a soft material like clay.

Question 6

How are castings made?

Answer 6

The dead organism is buried by a soft material. The clay later hardens around it and the organisms decays, leaving a cast of itself

Question 7

An animal’s [ ] or a plant’s [ ] can be preserved as casts

Answer 7

Burrow

Roots

Question 8

How does an impression happen?

Answer 8

Things like footprints can be pressed into these materials when soft, leaving an impression when it hardens

Question 9

What is amber?

Answer 9

A clear yellow ‘stone’ made from fossilised resin

Question 10

Describe preservation

Answer 10

1) In amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive

Question 11

In glaciers it’s too cold for the [ ] to work

Answer 11

decay microbes

Question 12

Why can’t microbes survive in peat bogs?

Answer 12

They’re too acidic for decay microbes

Question 13

Name some conditions where decay microbes can’t survive

Answer 13

1) Amber
2) Peat bogs
3) Glaciers
4) Tar pits

Question 14

What do fossils show?

Answer 14

How today’s species have evolved

Question 15

Name some theories for how life started

Answer 15

primordial soup
under the sea
Comets

Question 16

Briefly describe the ‘comet’ theory

Answer 16

Simple organic molecules were brought to earth on comets. These could have then become more complex organic molecules, and eventually simple life forms

Question 17

Why can’t the theories for how life started be supported or disproved?

Answer 17

Lack of valid and reliable evidence

Question 18

Why is there a lack of evidence for theories for how life started? (2)

Answer 18

1) There’s a lack of evidence because scientists believe many early organisms were soft bodied and soft tissue tends to decay away completely. So the fossil record is incomplete
2) Fossils that formed millions of years ago may have been destroyed by geological activity

Question 19

What causes extinction?

Answer 19

Extinction happens if you can’t evolve fast enough

Question 20

List the reasons why extinction happens: (6)

Answer 20

1) The environment changes too quickly
2) A new predator kills them all
3) A new diseases kills them all
4) They can’t compete with another (new) species for food
5) A catastrophic event happens that kills them all
6) A new species develops (speciation)