In this artist's rendering, the left image shows what Earth looked like more than 140 million years ago, when India was part of an immense supercontinent called Gondwana. The right image shows Earth today.
HOW INDIA MOVED
- Based on the geologic record, India's migration appears to have started about 120 million years ago, when Gondwana began to break apart.
- India was sent adrift across what was then the Tethys Ocean — an immense body of water that separated Gondwana from Eurasia.
- India drifted along at an unremarkable 40 millimeters per year until about 80 million years ago, when it suddenly sped up to 150 millimeters per year. India kept up this velocity for another 30 million years before hitting the brakes — just when the continent collided with Eurasia.
SEE THE MOVEMENT OF THE CONTINENTS ACROSS TIME
- AND THEY ARE STILL SHIFTING.
This series of graphics shows how our land masses have separated from Pangaea into the distinct continents we have today. Using new techniques - namely high-resolution seismic tomography, geographical information systems and increased computing power - scientists are tracking the changes in better detail.
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DOUBLE TROUBLE FOR INDIA
- India was pulled northward by the combination of two subduction zones — regions in the Earth's mantle where the edge of one tectonic plate sinks under another plate.
- As one plate sinks, it pulls along any connected landmasses.
- The geologists reasoned that two such sinking plates would provide twice the pulling power, doubling India's drift velocity
This map shows how Nepal is situated near the border of India and Asia, where two tectonic plates are moving into one another. The Indian plate is continuing to move North at a few centimetres per year - causing tectonic activity, which in turn can lead to tremors and devastating earthquakes
EARTHQUAKE THAT MOVED KATHMANDU
- The earthquake that devastated Nepal and left thousands of people dead shifted the earth beneath Kathmandu by up to several metres south, but the height of Mount Everest likely stayed the same, experts said Tuesday.
- The massive 7.8-magnitude quake on Saturday was the Himalayan nation's deadliest disaster in more than 80 years, killing more than 4,300 people and causing massive destruction.
- According to early seismological data obtained from sound waves which travel through Earth after an earthquake, the ground beneath the capital Kathmandu may have moved about three metres (10 feet) southward, said University of Cambridge tectonics expert James Jackson.
Scientists solve mystery
of how the Himalayas were formed
India has been revealed at the fastest moving continent in history.
More than 140 million years ago, India was part of an immense supercontinent called Gondwana, which covered much of the Southern Hemisphere.
However, around 120 million years ago, what is now India broke off and started slowly migrating north, at about 5 centimeters per year - before a mysterious event about 80 million years ago caused the continent suddenly sped up, racing north at about 15 centimeters per year.
This is roughly twice as fast as the fastest modern tectonic drift.
The continental move finally stopped when collided with Eurasia about 50 million years ago, giving rise to the Himalayas.
For years, scientists have struggled to explain how India could have drifted northward so quickly.
Now geologists at MIT have offered up an answer: India was pulled northward by the combination of two subduction zones — regions in the Earth's mantle where the edge of one tectonic plate sinks under another plate.
As one plate sinks, it pulls along any connected landmasses.
USGS - Earth tectonic plates
Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere. (LiveScience)
The geologists reasoned that two such sinking plates would provide twice the pulling power, doubling India's drift velocity.
The team found relics of what may have been two subduction zones by sampling and dating rocks from the Himalayan region.
They then developed a model for a double subduction system, and determined that India's ancient drift velocity could have depended on two factors within the system: the width of the subducting plates, and the distance between them.
If the plates are relatively narrow and far apart, they would likely cause India to drift at a faster rate.
The group incorporated the measurements they obtained from the Himalayas into their new model, and found that a double subduction system may indeed have driven India to drift at high speed toward Eurasia some 80 million years ago.
'In earth science, it's hard to be completely sure of anything,' says Leigh Royden, a professor of geology and geophysics in MIT's Department of Earth, Atmospheric and Planetary Sciences.
'But there are so many pieces of evidence that all fit together here that we're pretty convinced.'
Royden and colleagues including Oliver Jagoutz, an associate professor of earth, atmospheric, and planetary sciences at MIT, and others at the University of Southern California have published their results this week in the journal Nature Geoscience.
'When you look at simulations of Gondwana breaking up, the plates kind of start to move, and then India comes slowly off of Antarctica, and suddenly it just zooms across — it's very dramatic,' Royden says.
In 2011, scientists believed they had identified the driving force behind India's fast drift: a plume of magma that welled up from the Earth's mantle.
According to their hypothesis, the plume created a volcanic jet of material underneath India, which the subcontinent could effectively 'surf' at high speed.
However, when others modeled this scenario, they found that any volcanic activity would have lasted, at most, for 5 million years — not nearly enough time to account for India's 30 million years of high-velocity drift.
Instead, Royden and Jagoutz believe that India's fast drift may be explained by the subduction of two plates: the tectonic plate carrying India and a second plate in the middle of the Tethys Ocean.
In 2013, the team, along with 30 students, trekked through the Himalayas, where they collected rocks and took paleomagnetic measurements to determine where the rocks originally formed.
From the data, the researchers determined that about 80 million years ago, an arc of volcanoes formed near the equator, which was then in the middle of the Tethys Ocean.
A volcanic arc is typically a sign of a subduction zone, and the group identified a second volcanic arc south of the first, near where India first began to break away from Gondwana.
The data suggested that there may have been two subducting plates: a northern oceanic plate, and a southern tectonic plate that carried India.
'Imagine it's easier to squeeze honey through a wide tube, versus a very narrow tube,' Royden says. 'It's exactly the same phenomenon.'
Royden and Jagoutz's measurements from the Himalayas showed that the northern oceanic plate remained extremely wide, spanning nearly one-third of the Earth's circumference.
However, the southern plate carrying India underwent a radical change: About 80 million years ago, a collision with Africa cut that plate down to 3,000 kilometers — right around the time India started to speed up.
The team believes the diminished plate allowed more material to escape between the two plates. Based on the dimensions of the plates, the researchers calculated that India would have sped up from 50 to 150 millimeters per year.
'It's a lucky coincidence of events,' says Jagoutz, who sees the results as a starting point for a new set of questions.
'There were a lot of changes going on in that time period, including climate, that may be explained by this phenomenon. So we have a few ideas we want to look at in the future.'
How geology repeatedly gives rise to monster earthquakes in Nepal
It's unfortunate, but also unsurprising: An even more powerful 8.2 quake hit in 1934, killing more than 10,000 people in Nepal and India.
The earthquakes that were experienced in India's Kangra Valley in 1905 and Pakistan's Kashmir region in 2005 left behind higher death tolls — 20,000 and more than 85,000, respectively.
And the geological record reveals evidence of potentially stronger quakes going back to the year 1100.http://www.nbcnews.com/storyline/nepal-earthquake/how-geology-gives-rise-repeatedly-monster-earthquakes-nepal-n349161
Plate Tectonics explained:
By Becky Oskin, LiveScience
The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth's core rises, and colder mantle rock sinks.
"It's kind of like a pot boiling on a stove," Van der Elst said. The convection drive plates tectonics through a combination of pushing and spreading apart at mid-ocean ridges and pulling and sinking downward at subduction zones, researchers think.
Scientists continue to study and debate the mechanisms that move the plates.
Mid-ocean ridges are gaps between tectonic plates that mantle the Earth like seams on a baseball.
Hot magma wells up at the ridges, forming new ocean crust and shoving the plates apart. At subduction zones, two tectonic plates meet and one slides beneath the other back into the mantle, the layer underneath the crust.
The cold, sinking plate pulls the crust behind it downward.
USGS - Types of plate boundaries
Many spectacular volcanoes are found along subduction zones, such as the "Ring of Fire" that surrounds the Pacific Ocean.
Subduction zones, or convergent margins, are one of the three types of plate boundaries. The others are divergent and transform margins.
At a divergent margin, two plates are spreading apart, as at seafloor-spreading ridges or continental rift zones such as the East Africa Rift.
Transform margins mark slip-sliding plates, such as California's San Andreas Fault, where the North America and Pacific plates grind past each other with a mostly horizontal motion.
While the Earth is 4.54 billion years old, because oceanic crust is constantly recycled at subduction zones, the oldest seafloor is only about 200 million years old.
The oldest ocean rocks are found in the northwestern Pacific Ocean and the eastern Mediterranean Sea.
Fragments of continental crust are much older, with large chunks at least 3.8 billion years found in Greenland.
With clues left behind in rocks and fossils, geoscientists can reconstruct the past history of Earth's continents.
Most researchers think modern plate tectonics began about 3 billion years ago, based on ancient magmas and minerals preserved in rocks from that period.
"We don't really know when plate tectonics as it looks today got started, but we do know that we have continental crust that was likely scraped off a down-going slab [a tectonic plate in a subduction zone] that is 3.8 billion years old," Van der Elst said.
"We could guess that means plate tectonics was operating, but it might have looked very different from today."
As the continents jostle around the Earth, they occasionally come together to form giant supercontinents, a single landmass.
One of the earliest big supercontinents, called Rodinia, assembled about 1 billion years ago. Its breakup is linked to a global glaciation called Snowball Earth.
A more recent supercontinent called Pangaea formed about 300 million years ago. Africa, South America, North America and Europe nestled closely together, leaving a characteristic pattern of fossils and rocks for geologists to decipher once Pangaea broke apart.
The puzzle pieces left behind by Pangaea, from fossils to the matching shorelines along the Atlantic Ocean, provided the first hints that the Earth's continents move.
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