Where does evidence of early life forms come from?
Fossils.
Fossils?
Remains of organisms from many years ago, which are found in rocks.
What can we learn from fossils?
How much or how little organisms have changed since life developed on earth.
How can fossils form? 4
- hard parts don’t decay
- parts of an organism have not decayed due to the absence of conditions
- parts of an organism are replaced by other materials as they decay
- preserved traces of organisms
What were many early life forms and what does this mean?
Soft bodied and therefore left few traces behind.
What happened to the traces left behind by early life forms?
Mainly been destroyed by geological activity.
Why can’t scientists be sure about how life began?
Lack of valid and reliable evidence.
What is extinction caused by? 6
- new predators
- new, more successful competitors
- change in environment over geological time
- single catastrophic event
- new diseases
- new species developing
Speciation?
Development of new species.
Species?
A group of similar organisms which can reproduce to give fertile offspring.
When does speciation occur?
When populations of the same species become so different that they no longer breed to produce fertile offspring.
Stages of speciation? 4
- Isolation = 2 populations of species become separated
- Genetic variation = both populations show variation because there are a wide range of alleles
- Natural selection = alleles for the survival characteristics are selected as they are best suited to the environment and these organisms will survive to breed and pass on their characteristics to the next generation
- Speciation = the populations become so different that successful inbreedings is no longer possible
