- Study Of Fossil: fossil are dead remains of the the past organisms. The discovery and study of fossil provides evidence about the existence of these organisms.
- Formation of a time Sequence: The study of fossil allows biologists to place organisms in time Sequence . The fossil of these organisms are present in layers in a rock. When a geological time passed , new layers of sediments were performed. The older organisms moved to deeper layers or sediments were performed. The older organisms moved to deeper layers or sediments l (layer). Therefore, the sequence of the layers was not disturbed.
- Date/age of rock: age of rockbcan be determined by comparing the amount of certain radioactive isotopes present in it. The older sediments have less radioactive isotopes than the younger sediments. This comparison of layers gives relative age of the fossil found in this rock. Therefore, the fossils found in that same layer must be alive in the same geological period.
There are 4 era in Geological Time chart,
Proterozoic
Plaeozoec
Mesozoic
Cainozoic
Each are has periods.
- Proterozoic era has no period.
- Plaeozoic era has 6 periods, Cambrain, ordovacian, siluriun, devoniun, carbonefarius and Permiun.
- Mesozoic: era has 3 periods: Triassic, Jurassic, Creataceous.
- Canozoic: has 2 periods: Tertiary and Quaternary.
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