2.8.1 Old and new species

Question 1

Where does evidence for early life come form?

Answer 1

Evidence for early forms of life comes from fossils.

Question 2

How can fossils be formed?

Answer 2

■ from the hard parts of animals that do not
decay easily
■ from parts of organisms that have not decayed
because one or more of the conditions needed
for decay are absent
■ when parts of the organism are replaced by
other materials as they decay
■ as preserved traces of organisms, eg footprints,
burrows and rootlet traces.

Question 3

Why is it difficult to find traces of some animals?

Answer 3

Many early forms of life were soft-bodied, which
means that they have left few traces behind.
What traces there were have been mainly
destroyed by geological activity.

Question 4

What can fossils tell us?

Answer 4

We can learn from fossils how much or how little
different organisms have changed as life developed
on Earth.

Question 5

What can extinction be caused by?

Answer 5

■ changes to the environment over geological time
■ new predators
■ new diseases
■ new, more successful, competitors
■ a single catastrophic event, eg massive volcanic
eruptions or collisions with asteroids
■ through the cyclical nature of speciation

Question 6

How can new species arise?

Answer 6

■ isolation – two populations of a species become
separated, eg geographically
■ genetic variation – each population has a
wide range of alleles that control their
characteristics
■ natural selection – in each population, the
alleles that control the characteristics which
help the organism to survive are selected
■ speciation – the populations become so
different that successful interbreeding
is no longer possible.