From UPSC perspective, the following things are important :
Prelims level : Indian Plate
Mains level : Plate Tectonics Theory, Continental Drift Theory
- When the landmass that is now the Indian subcontinent slammed into Asia about 50 million years ago, the oxygen in the world’s oceans increased, altering the conditions for life.
Impact of Indian Plate
- The collision was already known to have changed the configuration of the continents, the landscape, global climate and more.
- Researchers used microscopic seashells to create a record of ocean nitrogen over a period from 70 million years ago – shortly before the extinction of the dinosaurs – until 30 million years ago.
Nitrogen dating to find Oxygen level
- Every organism on Earth requires “fixed” nitrogen – sometimes called “biologically available nitrogen.”
- Nitrogen has two stable isotopes: 15N and 14N. In oxygen-poor waters, decomposition uses up “fixed” nitrogen.
- This occurs with a slight preference for the lighter nitrogen isotope, 14N, so the ocean’s 15N-to-14N ratio reflects its oxygen levels.
- That ratio is incorporated into tiny sea creatures called foraminifera during their lives, and then preserved in their shells when they die.
- By analysing their fossils researchers were able to reconstruct the 15N-to-14N ratio of the ancient ocean, and therefore identify past changes in oxygen levels.
Why study oxygen?
- Oxygen controls the distribution of marine organisms, with oxygen-poor waters being bad for most ocean life.
- Many past climate warming events caused decrease in ocean oxygen that limited the habitats of sea creatures, from microscopic plankton to the fish and whales that feed on them.
- Scientists trying to predict the impact of current and future global warming have warned that low levels of ocean oxygen could decimate marine ecosystems, including important fish populations.
- The researchers found that in the 10 million years after dinosaurs went extinct, the 15N-to-14N ratio was high, suggesting that ocean oxygen levels were low.
- They first thought that the warm climate of the time was responsible, as oxygen is less soluble in warmer water.
- Global climate was not the primary cause of this change in ocean oxygen and nitrogen cycling.
Movement of Indian Plate
- Until roughly 140 million years ago, the Indian Plate formed part of the supercontinent Gondwana. It was a large island situated off the Australian coast, in a vast ocean.
- The Tethys Sea separated it from the Asian continent till about 225 million years ago.
- India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea
- India collided with Asia about 40-50 million years ago causing rapid uplift of the Himalayas.
- The positions of India since about 71 million years till the present are shown in the Figure. It also shows the position of the Indian subcontinent and the Eurasian plate.
- About 140 million years before the present, the subcontinent was located as south as 50◦ S. latitude. The two major plates were separated by the Tethys Sea and the Tibetan block was closer to the Asiatic landmass.
- During the movement of the Indian plate towards the Asiatic plate, a major event that occurred was the outpouring of lava and formation of the Deccan Traps. This started somewhere around 60 million years ago and continued for a long period of time.
- Note that the subcontinent was still close to the equator. From 40 million years ago and thereafter, the event of formation of the Himalayas took place.