9. Geological Time Scale
The earth is believed to be 4.5 billion years old. The 4.5 billion year long history of the earth is divided into four era - Pre-Cambrian, Palaeozoic, Mesozoic and Calnozoic. Pre-Cambrian has been the longest era in the earth’s history and it continued from the origin of earth to about 600 million year ago from today. The eras are divided into periods, and the periods are divided in to epochs. A brief account of the geological history of the earth is given in the following table:
Eons | Era | Period | Epoch | Age/Years Before Present | Life/ Major Events |
Cainozoic (From 65 million years to the present times) | Quaternary | Holocene Pleistocene | ♤ - 10,000 10,000 - 2 million | Modern Man Homo Sapiens | |
Tertiary | Pliocene Miocene Oligocene Eocene Palaeocene | 2 - 5 million 5 - 24 million 24 - 37 Ma 37 - 58 Million 57 - 65 Million | Early Human Ancestor Ape: Flowering Plants and Trees, Anthropoid Ape Rabbits and Hare Small Mammals : Rats – Mice | ||
Mesozoic 65 - 245 Million Mammals | Cretaceous Jurassic Triassic | 65 - 144 Million 144 - 208 Million 208 - 245 Million | Extinction of Dinosaurs Age of Dinosaurs Frogs and turtles | ||
Palaeozoic 245 - 570 Million | Permian Carboniferous Devonian Silurian Ordovician Cambrian | 245 - 286 Million 286 - 360 Million 360 - 408 Million 408 - 438 Million 438 - 505 Million 505 - 570 Million | Reptile dominate-replace amphibians First Reptiles: Vertebrates: Coal beds Amphibians, First trace of life on land: Plants, First Fish No terrestrial Life: Marine Invertebrate | ||
Proterozoic Archean Hadean | Pre- Cambrian 570 Million - 4,800 Million | 570 - 2,500 Million 2,500 - 3,800 Million 3,800 - 4,800 Million | Soft-bodied arthropods Blue green Algae: Unicellular bacteria Oceans and Continents form – Ocean and Atmosphere are rich in Carbon dioxide | ||
Origin of Stars Supernova Big Bang | 5,000 - 13,700 Million | 5,000 Million 12,000 Million 13,700 Million | Origin of the sun Origin of the universe |
Questions:
1. Gliese 581g (UPSC 2011/2 Marks)
2. What does the solar system consists of? Discuss the motion of the entire solar system as a whole and also the motion of most of the bodies forming the solar system. (UPSC 2003/ 15 Marks)
3. What is the difference between a comet and a meteor? (UPSC 1997/3 Marks)
4. Why does a lunar eclipse occur only on a full moon? (UPSC 1996/3 Marks)
5. What is a leap second? (UPSC 1992/3 Marks)
6. What is ‘Chandrashekhar limit’? (UPSC 1985/3 Marks)
7. Astronomers have, of late, been discussing ‘black hole.’ What is a ‘black hole’?(UPSC
1979/3 Marks)
8. What is the ‘diamond ring effect’ observed during a total solar eclipse? How is it caused? (UPSC 1979/3 Marks)
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