Geological history of India, earth and life
The planet earth was formed about 4.54 billion years ago and life appeared on its surface within a billion years of its formation.
The mass of the Earth is approximately 6 × 1024 kg composed mostly of iron (32 %), oxygen (30 %), silicon (15%), magnesium (14%), sulfur (3 %), nickel (2 %), calcium (1.5%), aluminum (1.4%) and the remaining amounts of other elements.
Earth’s internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). At the center of the planet, the temperature may be up to 7,000 C.
The outer layer of the Earth is a chemically distinct is solid crust, which is underlain by a highly viscous solid mantle. The thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. Underneath the crust lies the much hotter mantle and plumes of super-heated rock occasionally erupt out of this layer, causing hotspots of volcanic activity. The temperature of the crust increases with depth, reaching values typically in the range from about 200° to 400°C at the boundary with the underlying mantle.
The average age of the current Earth’s continental crust has been estimated to be about 2.0 billion years. The Earth’s crust is not a stationary shell but an ever-shifting mosaic of tectonic plates that constantly (albeit slowly) reshape the face of the planet.
Around 600 million years ago (Ma), most of these plates came back together to form the relatively short-lived supercontinent of Pannotia, and only 60 million years after its formation, about 540 Ma, near the beginning of the Cambrian epoch, Pannotia broke up, giving rise to the continents of Laurentia, Baltica and the southern super continent of Gondwana which included Africa, Australia, South America, Antarctica, India and Arabia. Before that time, all organisms were aquatic, including simple algae, fungi, several phyla of invertebrates, and a few vertebrates such as fish and around that time the first land-dwelling organisms appeared, including simple plants and arthropods.
By about 180 Ma, nearly all the land was pretty much united in once again in a large continent called Pangea, and thus, all the water was in one large ocean called Panthalassa. This time period is the Jurassic Period of the Mesozoic Era, and has been nicknamed the “age of dinosaurs” because of their prominence. In addition to dinosaurs, there were many species of cockroaches, other reptiles, and gymnosperms including conifers and cycads. It is thought that the very first birds and mammals appeared near the end of this time period.
Sometime between 180 and 120 Ma, Pangea started to break apart. The northern continent formed from this was called Laurasia and consisted of what are now North America, Greenland, Europe, and Asia. The climate included warm, tropical and subtropical areas. Because of the warmth, the oceans were high and covered much of the land, limiting movement. During this time, angiosperms, mammals, birds, appeared.
At bout 120 Ma, Gondwana, the southern continent, broke into three pieces, including South America/Africa, India, and Australia/Antarctica. At this time, India started going its own way. At about 100 Ma, South America and Africa split. 90 Ma, India rifted away from Madagascar and began its rapid movement northward. During the late Cretaceous (80 – 65 Ma), India was moving at rates of more than 15 cm/year, ultimately colliding with Asia between 55-50 Ma. No modern plate moves that fast. After India collided, Australia was released from Antarctica and it began to move northward towards S. E. Asia.
On the boundary between Cretaceous and Tertiary periods (65 Ma to 1.64 Ma), the Deccan traps, huge lava flows all over the Indian peninsula, were formed. During the transition between the Oligocene (35.4 Ma to 23.3 Ma) and Miocene (23.3 Ma to 5.2 Ma), the Himalayas started rising. The region between the peninsula and the Himalayas was the 2–6,000 meter deep Tethys sea which slowly got filled with silt from the preexisting rivers, and during the Pleistocene (1.8 Ma to 10 Ka) formed the Indus-Ganges-Brahamaputra plain.
Since that period, India has probably occupied the same latitudes, and hence a similar climate, except, of course, due to the vagaries of the global climactic conditions.
The ice ages occurred about 2 Ma. Ice sheets and glaciers separated populations of organisms which, being then in different habitats, had different selective pressures acting on their alleles and thus evolved into different species. This has resulted in the large variety/number of species we see today. During the ice age, the Himalayan snowline was probably down to 1800 meters instead of the current 4000 meters above sea level, and even in later Pleistocene, the sea level was probably 100 to 150 meters lower than what it is today, easily connecting all of Andamans into one island, and connecting the Ceylonese island to India. On the other hand during the interglacials, around 120 Ka and 30 Ka, the sea level might have been higher than now.