Where does evidence of early life come from?
Fossils
What are fossils?
The remains of organisms from many years ago
Fossils can be formed from the hard…
Parts of animals that don’t decay easily
Fossils can be formed from parts of…
Organisms that have not decayed because one or more of the conditions needed for decay are absent
Fossils can be formed when parts of the…
Organism are replaced by other materials as they decay
Fossils may be formed as preserved…
Traces of organisms, e.g. footprints, burrows and rootlet traces
What were many early life forms?
Soft bodied, which means they have left very few traces behind
How have many traces of early life forms been destroyed?
By geological activity
What can we learn from fossils?
How much or how little different organisms have changed as life developed on Earth
What may extinction be caused by?
Changes to the environment over geological time, new predators, new diseases, new and more successful competitors, a single catastrophic event for example astroids or volcano eruptions and through the cyclical nature of speciation
What is the first step of a new species arising?
Isolation- two populations of the same species become geographically seperated
What is the second stage of a new species arising?
Genetic variation- in each population there is a wide range of alleles that control their characteristic
What is the third step of of a new species arising?
Natural selection- In each population, the organisms which possess the alleles that control the characteristics which help the organisms survive the best in their different environments, survive and pass on the alleles to their offspring
What is the fourth stage of a new species arising?
Speciation- the populations become so different due to their different adaptations to suit their different environments, that successful interbreeding between the once similar species is no longer possible
