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Here's How Peru's Ancient People Survived in the Treacherous Andes

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Earth's interior is sucking ocean water exceeding the amount it gives back, says a study

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It was well known that the earth drags sea water at trenches but a seismic study reveals that the amount of water dragged is about three times more than previously thought. The phenomenon has major implications for the global water cycle.

The findings showed that the loss of seawater is due to the slow-motion collisions of tectonic plates under Mariana Trench — deepest ocean trench in the world. The trench is where the western Pacific Ocean plate slides beneath the Mariana plate and sinks deep into the Earth’s mantle as the plates slowly converge.

Subduction zones suck in water

“People knew that subduction zones could bring down water, but they didn’t know how much water,” said lead author Chen Cai, from the Washington University in St. Louis.

“This research shows that subduction zones move far more water into Earth’s deep interior, many miles below the surface than previously thought,” added Candace Major, a programme director in the National Science Foundation’s Division of Ocean Sciences.

Ocean water seeps into mantle along the fault lines

For the study, published in the journal Nature, the team listened to more than one year’s worth of Earth’s rumblings — from ambient noise to actual earthquakes — using a network of 19 passive, ocean-bottom seismographs deployed across the Mariana Trench, along with seven island-based seismographs.

They found that ocean water atop the plate runs down into the Earth’s crust and upper mantle along the fault lines that lace the area where plates collide and bend. Then it gets trapped.

Under certain temperature and pressure conditions, chemical reactions force the water to get trapped into the rock in the geologic plate as a non-liquid form– hydrous minerals.

Then, the plate continues to crawl ever deeper into Earth’s mantle, bringing the water along with it.

Also read | Luni, the Indian river with saline water that doesn’t drain into any sea or ocean: Facts you need to know

Earth is giving lesser water than it is taking

The seismic images show that the area of hydrated rock at the Mariana Trench extends almost 20 miles or 32.2 km beneath the seafloor, the study showed.

For the Mariana Trench region alone, four times more water subducts than previously calculated.

These features can be extrapolated to predict the conditions under other ocean trenches worldwide. Scientists believe that most of the water that goes down at the trench comes back from the Earth into the atmosphere as water vapour when volcanoes erupt hundreds of miles away.

But with the revised estimates of water, the amount of water going into the earth seems to greatly exceed the amount of water coming out, the researchers noted.

What is a subduction zone?

Tectonic plates can transport both continental crust as well as oceanic crust. The latter is denser than the former and when these two collide, the oceanic crust (denser) sinks into the mantle beneath the oceanic crust (lighter). This forms a subduction zone like trenches.

The deepest trench on Earth is the Mariana trench which lies in the Pacific Ocean and has a depth of 11,034 m.

Also read | Super Earth or exoplanet? This new planet is most likely to support alien life

Also read | New planet twice the size of Earth found revolving around orange dwarf star

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Crater found under Greenland's ice among the 25 largest impact craters on Earth

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An international team led by researchers from the Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen, discovered a 31-kilometre wide meteorite impact crater buried beneath the ice-sheet in Greenland’s Hiawatha Glacier.

If confirmed, it would be the first impact crater discovered under one of Earth’s continental ice sheets, said researchers from the University of Copenhagen in Denmark.

Signs of the crater were first detected by NASA’s Operation Icebridge, an airborne mission that uses radar to track changes in ice on Greenland’s ice sheet.

The researchers worked for the last three years to verify their discovery, initially made in 2015.

All about the crater

[embedded content]

According to the study published in the journal ‘Science Advances,’ the crater measures more than 31 km in diameter, corresponding to an area bigger than Paris and larger than Washington DC, which places it among the 25 largest impact craters on Earth.

What are impact craters?

An impact crater is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial bodies, caused by a collision of a smaller body (meteor) with the surface.

How did such a big crater form?

Map of the bedrock topography beneath the ice sheet and the ice-free land surrounding the Hiawatha impact crater. The structure is 31 km wide, with a prominent rim surrounding the structure.(Image: Natural History Museum of Denmark)

The crater formed when a kilometre-wide iron meteorite smashed into northern Greenland but has since been hidden under nearly a kilometre of ice.

“The crater is exceptionally well-preserved, and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact,” said Professor Kurt H Kjaer from the Natural History Museum of Denmark.

“So far, it has not been possible to date the crater directly, but its condition strongly suggests that it formed after ice began to cover Greenland, so younger than three million years old and possibly as recently as 12,000 years ago – toward the end of the last ice age,” he said.

When was it first discovered?

Close-up of the northwestern ice-sheet margin in Inglefield Land. The Hiawatha impact crater was discovered beneath the semi-circular ice margin.(Image: Natural History Museum of Denmark)

The crater was first discovered in July 2015 as the researchers inspected a new map of the topography beneath Greenland’s ice-sheet.

“Previous radar measurements of Hiawatha Glacier were part of a long-term NASA effort to map Greenland’s changing ice cover,” Joe MacGregor, a glaciologist with NASA, explains.

“What we really needed to test our hypothesis was a dense and focused radar survey there. The survey exceeded all expectations and imaged the depression in stunning detail: a distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris – it’s all there.”

They noticed an enormous, but previously undetected circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northern Greenland.

“We immediately knew this was something special but at the same time it became clear that it would be difficult to confirm the origin of the depression,” said Kjaer.

The 20-tonne iron meteorite sits in the courtyard at the Geological Museum in Copenhagen.

Also read | This new Artificial Intelligence technique just found 6,000 new craters on Moon

Also read | Top seven impactful largest craters unearthed in the past few years

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Large meteorite impact crater found beneath Greenland ice sheet

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An international team of researchers has unearthed a large impact crater under more than a half-mile of ice in northwestern Greenland’s

Measuring roughly 1,000 feet deep and more than 19 miles in diameter, the crater — the first of any size found under the ice sheet — is one of the 25 largest impact craters on Earth, the researchers said.

According to the study, published in the journal Science Advances, the crater formed less than 3 million years ago when an iron more than half a mile wide smashed into northwest

The resulting depression was subsequently covered by ice.

“The crater is exceptionally well-preserved and that is surprising because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact,” said Kurt Kjaer, at the

The tectonic structures in the rock near the foot of the glacier as well as the samples of sediments washed out from the depression confirm that the glacier is a crater.

“Some of the quartz sand coming from the crater had planar deformation features indicative of a violent impact; this is conclusive evidence that the depression beneath the is a meteorite crater,” explained Nicolaj Larsen, Associate at in

In July 2015, the scientists first noticed an enormous, previously unexamined circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northwestern

Using NASA’s Terra and Aqua satellites, they examined the surface of the ice in the region and quickly found evidence of a circular pattern on the ice surface that matched the one observed in the bed topography map.

In May 2016 they mapped the crater and the overlying ice over the Hiawatha Glacier.

“The survey imaged the depression in stunning detail: a distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris – it’s all there,” said Joe MacGregor, a NASA glaciologist at in

Kjaer noted that the crater’s condition indicates that the impact might even have occurred toward the end of the last ice age, which would place the resulting crater among the youngest on the planet.

–IANS

rt/mag/bg

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)

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