Story of the Earth
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"Continental drift." Earth, Story of the Earth, Q-files Encyclopedia, 20 Nov. 2023.
https://www.q-files.com/earth/story-of-the-earth/continental-drift.
Accessed 19 Mar. 2024.
Continental drift 2023. Earth, Story of the Earth. Retrieved 19 March 2024, from
https://www.q-files.com/earth/story-of-the-earth/continental-drift
Earth, Story of the Earth, s.v. "Continental drift," accessed March 19, 2024.
https://www.q-files.com/earth/story-of-the-earth/continental-drift
Continental drift
The vast landmasses we call the continents have not always been where they are today. Earth’s outer shell is divided up into large slabs, called tectonic plates. These plates, which include both the continents and the floors of the oceans, shift very slowly about. This is called continental drift, part of the process known as plate tectonics. Over hundreds of millions of years, the continents have drifted around the globe, while the oceans have widened or narrowed accordingly. Just looking at a map of the world today gives us clues of where the continents were once positioned. It is easy to imagine South America, for example, tilted slightly and fitted snugly into the western coast of Africa—which is exactly where it was 135 million years ago.
The break-up
of Pangaea
Over hundreds of millions of years, entire continents have wandered around the globe, colliding into one another or drifting apart. About 280 million years ago, they came together to form a single “supercontinent” called Pangaea. There was no Atlantic Ocean, and the Americas were jammed up against Africa and Europe.
Since then, the continents have slowly split apart again, although some pieces, such as India and Asia, have collided with each other. During the Jurassic Period (201–145 million years ago), the continents began to move apart. Pangaea separated into two: Laurasia and Gondwana. This drift continued through the Cretaceous Period (145–66 million years ago). The continents are still in motion today.
India moves north
Gondwana (or Gondwanaland) was the more southerly of two supercontinents that once formed Pangaea. It included most of today's landmasses of the Southern Hemisphere: Antarctica, South America, Africa, Madagascar and Australia. It also included the Arabian Peninsula and the Indian subcontinent, but these two landmasses have since separated and drifted northwards into the Northern Hemisphere.
By around 100 million years ago, India had broken away from Gondwana. It was now a large island situated off the Australian coast and separated from Asia by the Tethys Sea. India then started its northward drift towards Asia. About 80 million years ago, India still lay 6400 kilometers (4000 miles) south of the Asian continent, but now accelerated towards it at a rate of up to 16 centimetres (6 inches) per year, about twice as fast as any tectonic plate is moving today.
India began to collide with Asia between 55 and 35 million years—geologists are not sure exactly when. But, instead of one plate being forced to slide beneath the other, as happened in other parts of the world, both Indian and Asian plates crunched together and buckled up into the great mountain range we know today as the Himalayas, the tallest mountains on Earth.
The Himalayas are still rising by more than a centimetre (roughly half an inch) per year as India continues to move northwards. This causes earthquakes in the region today—like, for example, the catastrophic quake that devastated Nepal in April 2015. The forces of weathering and erosion are, however, lowering the Himalayas at about the same rate.
Evidence
Fossils provide evidence for continental drift. The discovery of fossils of Lystrosaurus, a Triassic reptile, in South Africa, Antarctica and India, proves that these lands were once joined together. How else could this land reptile have lived in all three places?
Another important piece of evidence is the presence of glacial sediments from the same time in geological history in South America, Africa, Madagascar, the Arabian Peninsula, India, Antarctica and Australia. The sediments were laid down while these landmasses were all part of one "supercontinent", which then later drifted apart.
Future drift
Continental drift is continuing today—just like it has for hundreds of millions of years. This map, above, shows how the world's continents (shown in green) may look 50 million years from now, with the tectonic plates having shifted from their present positions (outlined in blue). The Atlantic Ocean has spread apart. North and South America are no longer joined together at the Isthmus of Panama. Africa and Asia have split at the Red Sea, while the Great Rift Valley has become an arm of the Indian Ocean. Australia has collided with Indonesia.
In the distant future all the current continents might merge together to form a new supercontinent. In the era of what scientists describe as "Pangaea Proxima" (or Pangaea Ultima), 250 million years from now, temperature extremes are expected to be dramatic, with severe arid conditions in the vast inland deserts. Greater volcanic activity would put twice as much carbon dioxide into the atmosphere as current levels.
The world could return to the extreme heat it last endured at the end of the Permian Period, 260 million years ago. More than 90% of species went extinct at the time, known as The Great Dying. Extended periods of heat in excess of 40°C would be beyond the tolerance levels of most mammals—including humans.
Consultant: Ian Fairchild