Fossils and Speciation Flashcards
What are fossils?
The remains of organisms from many years ago which are formed in rocks.
What can fossils show us?
How life on Earth has evolved - by comparing fossils with modern species we can see how organisms have changed over millions of years.
What are the three ways fossils form?
- Gradual replacement by minerals
- From casts and impressions
- Preservation
How can fossils be made by gradual replacement by minerals?
Things like bones and shells don’t decay very easily so are replaced by minerals as decay slowly happens. The minerals form a rock-like substance with the same shape as the original part.
How can fossils form from casts and impressions?
An organism is burrows in soft material like clay which hardens around it while the organism decays. This leaves a cast in the material.
How can fossils be formed by preservation?
If the conditions don’t have enough oxygen, enough moisture or have the right temperature and pH, an organism won’t decay so its remains will be preserved.
What are two theories on the origins of life on Earth?
- Primordial soup
* Organic molecules carried by comets to Earth
Why is it difficult for scientists to know how life on Earth began?
There is a lack of evidence due to our incomplete fossil record.
Why is the fossil record incomplete?
- It is believed that early organisms were soft bodied so could have decayed without forming fossils
- Fossils from long ago could have been destroyed by geological activity
What is extinction?
When an entire species ceases to exist.
What are six reasons why a species can become extinct?
- The environment changes too quickly for them to adapt
- A new predator kills them
- A new disease kills them
- Competition with a new species
- A catastrophic event like a volcanic eruption
- A new species develops
What is speciation?
The development of a new species.
What is isolation?
When populations of a species are separated by a physical barrier like a mountain or a river.
How does natural selection work?
1) Two populations become isolated
2) Each population shows variation because they have a wide range of alleles
3) In each population individuals with characteristics that make them better adapted to their environment have a better chance of survival so are more likely to breed
4) The alleles that control beneficial characteristics are more likely to spread
5) This keeps happening until the two populations will no longer be able to breed to produce fertile offspring.
