The Origins of Life on Earth
It is believed that life on Earth is about 4500 million years old and that life began about 3500 million years ago.
There is some debate as so whether the first life developed due to the conditions on the Earth or whether simple life forms arrived from another planet.
We can date rocks. Fossils are found in rocks so we can date when different organisms exsisted. We can do this becasue fossils and rocks are found in different layers, the deeper they are, the older they are.
Theories of Evolution
Lamarcks theory stated that accquried charatricstics can be passed on to the next generation. People found this difficult to believe. For example, if two parents were to built up there muscles in the gym, Lamarcks theory said that this characteristic would be passed on to the offsprng.
Darwins theory stated that small changes took place over time. All organisms vary and therefore some are more likely to survive (natural selection.) Those that are best adapted breed and pass along charatristics.
It took a long time for Darwins theory to be accepted. Many people wanted to believe that God was resposible for the creation of a new species.
Due to sexual reproduction, there is variation between members of a species. For example, all antelop are different to each other. Those members of a species with the 'best' charactristics survive to breed.
Weaker members of the species may die from:
- Lack of food.
- Being caught be predators.
- Variation in the climate (a very wet or dry/ hot or cold period of weather.)
The survival of organisms with the 'best' charactristics is known as the survival of the fittest.
The fact that the best adapted animals and plants survive is known as natural selection.
Extinction means that a species that once exsisted has been competely, wiped out.
Extinction can be caused by a number of factors, but always involves a change in circumstances:
- A new disease may kill all members of a species.
- Climate change may make it too cold or too hot, or too wet or too dry, for a species and reduce its food supply.
- A new predator may evolve or be introduced into a new area and it eats the species.
- A new competitor may evolve or be introduced into an area. The original species may be left with too little to eat.
- The habitate the species live in may be destroyed.