(ii) Carbon (C14) Dating Technique: This methods was introduced by W.F.Libby in 1950. Radioactive carbon (C14) in found naturally in rock. C14 has a half life of 5600 years and C14 decay gives nitrogen(N14). Cabon dating technique can be used to measure fossil age upto 25,000 years old.
(iii) Potassium-Argon Technique: Radioactive Potassium (K40) is usually found in the rock of all kinds. Its life is 1.3x109 years and disintegrate to form Argon.
Geological Time Scale: Use of the radioactive dating has allowed the determination of fossils found in different sedimentary rock samples. It has allowed to calculate the presence of different organisms preserved in the rock samples in the form of fossils. In addition, it helped scientist to predict that earth is almost 4-5 billion year old and life appeared on earth almost 4000 millions year ago. Since then the earth’s history has been divided into 5 different time frame known as eras. Few of these eras are divided into the periods and which inturn split up into the epochs. The different Eras are as follows:
1. Archeozoic (4600-3500 millions year): it is thr first era and begins with the formation of earth and presence of solar system. There is no fossil form available from this era.
2. Proterozoic (3000-1000 millions year): it is the second era and begins with the origin of prokaryotes, primitive metazoans and eukaryotes. Reports are available about scanty fossils in this era.
3. Palaeozoic (570-280 millions year): it is the third era and known as era of ancient life. It saw the appearance of invertebrate, fishes, amphibian etc. Reports of spore bearing plants, tree ferns and origin of conifers is available. initial Reports are available about scanty fossils in this era.
4. Mesozoic (225-135 millions year): The appearance of tooth birds, therian mammals, reptiles and dominance of dinosaurs. In addition, placental mammals are also found. Reports of cycads and flowering plants is available.
5. Cenozoic (Modern era): This is the modern era and it witnessed the dominance of present age man, modern mammals, birds, fishes and insects.