Old and new species - key points

The origins of life on Earth
1. Fossils give us information about organisms that lived millions of years ago.
2. Fossils may be formed in different ways.
3. Fossils are the remains of organisms from many years ago that are found in rocks
4. It is very difficult for scientists to know exactly how life on Earth began because there is little evidence that is valid.
Isolation and the evolution of new species
1. There are natural cycles linked to environmental change when species form and when species die out.
2. In an isolated population alleles are selected that increase successful breeding in the new environment
3. Speciation takes place when an isolated population becomes so different from the original population that successful interbreeding can no longer take place
4. Populations become isolated when they are separated geographically, e.g. on islands
5. New species arise when two populations become isolated
Exploring the fossil evidence
1. We can learn from fossils how much or how little organisms have chaned as life has developed on Earth
2. Extinction may be caused by new predators, new disease or new, more successful competitios.
More about extinction
1. Extinction can be caused by environmental change over geological time
2. Mass extinction may be caused by single catastrophic events such as volcanoes or asteroid strikes.

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