B2.8 Fossils and Speciation

Question 1

What are fossils?

Answer 1

The remains of organisms from many years ago, which are found in rocks

Question 2

What do fossils show?

Answer 2

How life on earth has evolved

Question 3

How do fossils show how life on earth has evolved?

Answer 3

Because fossils can be compared with species that are alive today

Question 4

What are the three ways a fossil can form?

Answer 4

From gradual replacement by minerals, from casts and impressions or from preservation in places where no decay happens

Question 5

How does the gradual replacement of minerals form fossils?

Answer 5

Things like teeth, bones and shells don’t decay easily and can last a long time when buried - when they do decay, minerals replace them which holds the shape of the original hard part

Question 6

How do casts and impressions form fossils?

Answer 6

When an organism is buried in a soft material like clay; the clay hardens around the organism and the organism decays leaving a clay cast

Question 7

What will fossilise in casts and impressions? (2)

Answer 7

Animal’s burrows and plant’s roots

Question 8

How do fossils form from the preservation in places where no decay happens?

Answer 8

Microbes involved in decay need the right conditions in order to break down materials (e.g. plenty of oxygen, enough moisture and the right temp + pH), remove these conditions and the dead organism’s remains will be preserved

Question 9

Where would no decay occur for an organism to be preserved? (2)

Answer 9

In amber, and in bogs

Question 10

Why is there a lack of valid and reliable evidence to prove hypotheses for the origin of life on earth? (2)

Answer 10

Scientists believe early organisms were soft-bodied which meant they decayed away completely without forming fossils, and many fossils have been destroyed due geological activity e.g. the movement of tectonic plates may have crushed fossils

Question 11

If we don’t have a fossil of every organism which has lived on Earth, what do we have?

Answer 11

An incomplete fossil record

Question 12

What is extinction?

Answer 12

When species no longer exist

Question 13

Why do species become extinct? (6)

Answer 13

When there is a sudden change in environment, when a new predator kills them all, a new disease kills them all, they can’t compete for food due to other more adapted species, a catastrophic event kills them all or a new species develops

Question 14

What is a species?

Answer 14

A group of similar organisms that can reproduce to give fertile offspring

Question 15

What is speciation?

Answer 15

The development of a new species

Question 16

What is isolation?

Answer 16

Where populations of a species are separated, possibly due to a physical barrier e.g. a flood, isolation leads to speciation

Question 17

What is natural selection?

Answer 17

When two populations of the same species going through isolation, and they adapt to their environments to a point at which they can no longer breed fertile offspring

Question 18

Can you explain natural selection? (3)

Answer 18

1. Each population shows variation due to a wide range of alleles
2. Individuals with characteristics which help them to survive are more likely to breed successfully
3. So the alleles which control the beneficial characteristics are more likely to be passed on to the next generation