Fossils and extinction

Question 1

What is a fossil?

Answer 1

• Anything left behind by a long-dead organism

Question 2

How do fossils help us see how a species has evolved?

Answer 2

• Most species that have ever lived are now extinct
• Looking at things that they have left behind show us how organisms have changed (through small incremental changes in their bodies) and provide evidence for evolution

Question 3

Explain how fossils are made through gradual replacements of minerals

Answer 3

• Body parts such as bone, teeth and shells decay very slowly. As they decay, they are replaced by minerals
• This forms rock-like substances that are the same shape and size as the original bone / teeth

Question 4

Explain how casts & impressions are made

Answer 4

• Casts:
• When an animal is buried in a soft material like clay
• As the clay hardens, they animal inside decays. This leaves a mould with a gap inside that is of the same shape and size as the animal
• Impressions:
• Marks left behind by animals on ground (footprints) that are covered in layers of sediments and preserved

Question 5

Explain how preservation of animal remains occur

Answer 5

• Conditions where there is no oxygen or moisture (such as tar pits) so decay cannot take place
• Animal remains completely intact

Question 6

Why do we have incomplete fossil records?

Answer 6

• The oldest fossils span ~4 billion years ago
• Any fossils formed longer ago have been destroyed due to tectonic movements (volcanoes / earthquakes) or have been destroyed as soft-bodied organisms decay quickly
• This leaves incomplete fossil records

Question 7

What are some common reasons for extinction?

Answer 7

• Environment changes too quickly
• Outcompete by new species
• Disease kills all animals of the species