Life on Earth
The Earth formed over 4.5 billion years ago. The oldest rocks are about 4.3 billion years old. They contain no signs of life. The earliest signs of life are formed in rocks just over 3.5 billion years old. They contain shapes which look like fossils of bacteria.
Fossils give us information about organisms that lived on Earth in the past. Some fossils are bones, others are just the shape of the organism, or some made from its tracks or even its faeces.
We can analyse rocks to find their age. If they contain fossils, this means that we know how long ago the organisms lived. Fossils can give us a picture of organisms which lived a long time ago and how they gradually changed with time.
There is debate as to whether the first life developed due to the conditions on Earth, or whether simple life forms arrived from another planet.
There is so little fossil evidence of bacteria because it is microscopic so are hard to find and they don't have skeletons or hard parts so they decay very quickly.
Formation of Fossils
Fossils are formed in various ways:
- from the hard parts of animals that do not decay easily, e.g. bones, shells or teeth, but may stay as the original material for quite some time, though eventually most become replaced by surrounding minerals
- from parts of organisms that haven't decayed because one or more of the conditions needed are absent e.g. mummification (conditions too dry and sterile)
- when parts of the organism are very gradually replaced by other materials as they decay, e.g. mineralisation from surrounding sediments of sand or shale layers,
- as preserved traces of organisms by way of casts and impressions in sedimentary rock layers, e.g. footprints, burrows and rootlet traces.
Ice fossils give us clear evidence of animals that lived in the past as it stops the decay process. The enzymes in bacteria can't work because it is too cold and therefore the animal is preserved well.
Most organisms that died did not leave a fossils because the exact conditions for fossil formation were not present. The main reasons are: Soft body organisms decay the most or Geological activity destroys fossils before we find them.
There are remains or whole fossils of organisms which lived in those places in the past which give evidence for the theory of evolution because they some gradual change of a long time. Organism may share a common ancestor which means an organism which many other organisms evolved from.
The theory of evolution states that all species of living things have evolved from simple life forms which first developed more than three billion years ago.
The mammoth, which was very hairy, and the elephant, are both thought to have evolved form a scantily haired ancestor. Explain, as fully as you can, how the mammoth evolved from the common ancestor.
The mammoth evolved from their common ancestor and at that time conditions were very cold so the common ancestor would have died out due to not having enough fur to keep it warm. But, there must have been variation in the species as the mammoths have evolved with a lot of fur so they don't get cold and survived from longer and mated, passing on their genes to their offspring.
Extinction is the permanent loss of a species from Earth.
Extinction could be caused by:
- New Predators: They wipe out the unexpected pray because the prey animals don't have adaptation to avoid them so they get killed and become extinct.
- New Diseases: (Caused by microorganisms) can bring species to the point of extinction. Most likely to cause extinction on islands where the whole population of an animal or plant are close together.
- Better Competition: New mutation can give one type of organism a real advantage over another. Sometimes new species are introduced to the environment by mistake. The new successful competition takes the food of the animal so it becomes extinct.
- Environmental Change: Temperatures on earth have risen to be very hot and other times to be almost ice age. Natural selection makes a certain species in their perfect climate thrive and the other dies out.
- Catastrophic Events(mass extinction): Usually for a relatively short time and on global scale. It happened over several millions of years. It could be a volcanic eruption or a giant asteroid by huge numbers of species disappear from earth.
Speciation is when a new species is formed.
Isolation and Evolution
Populations can become geographically isolated perhaps by a new river forms separating the species, pieces of land fragment break off into an island or a mountain range could form. Each population has a wide range of alleles that control their characteristics. This is genetic variation.
A new species will arise because there would be genetic variation in both populations because they are under different environmental pressures. The best adapted members of the species survive to the reproduce also new characteristics arise due to mutations. The isolated groups will gradually change differently due to different environmental pressures until they can no longer interbreed.
You can check if speciation has occurred by doing a DNA analysis or a breeding programme, bring together species to see if they will interbreed.
A species is said to be endemic when it evolves in isolation; one place in the world.