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Ancient DNA reveals two previously unknown migrations into South America

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Credit: Posth et al./Cell.

Scientists analyzed the ancient DNA of individuals who lived in Central and South America up to 10,000 years ago and found that these regions were settled by at least three waves of migration. The studies paint a rich and diverse history of the Americas, suggesting that the people who formed these migratory waves branched out of a single population that crossed the Bering Strait into North America about 15,000 years ago.

“Our work multiplied the number of ancient genomes available from these areas by about 20, giving us a much more comprehensive picture of indigenous history in the Americas,” co-senior author David Reich, a geneticist at Harvard Medical School and the Howard Hughes Medical Institute, said in a statement. “This broader dataset reveals a common origin of North, Central, and South Americans as well as two previously unknown genetic exchanges between North and South America.”

The DNA collected from 49 individuals who lived in Belize, Brazil, the Central Andes, and southern South America shows that they all originate from the same ancestral population that colonized North America. In and of itself, this fact is not particularly remarkable because scientists have always known that Central and South America were peopled by a migration that moved southward. However, what was truly surprising about the findings of three new ancient DNA studies, all published this week (Cell, ScienceScience Advances), was that there were multiple distinct migratory movements — some that mixed, others that formed new lineages.

Archaeologists believe that the Clovis people were the first to pass through the land bridge between Siberia and Alaska, which is now underwater, settling in the lower 48 states some 13,000 years ago. The Clovis culture was named after flint spearheads found in the 1930s at a site in Clovis, New Mexico. These mammoth-hunting people are considered to be the ancestors of most of the indigenous cultures of the Americas. Now, the new genomic analysis has yielded fresh insights into how Clovis people may have spread across the Americas.

Researchers compared the genome of a Clovis toddler who lived in Montana about 12,700 years ago to the earliest genome analyzed from South and Central America dating to between 9,000 and 11,000 years ago. The analysis revealed a common ancestry between the remains found in Montana and Lagoa Santa in Brazil, which suggests that the Clovis made a major impact much further south. Previously, anthropologists believed that the people at Lagoa Santa originated from a separate migration from Asia.

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“We weren’t expecting to find a relation to people associated with the Clovis culture in South America,” says co-first author Nathan Nakatsuka from Harvard. “But it seems the expansion of the Clovis-associated lineage extended to parts of Central and South America.”

From around 9,000 years ago, however, the Clovis culture-associated ancestry completely disappeared in Peru. We don’t know what was the cause of such a dramatic large-scale population replacement but what seems certain is that the region was populated by a separate wave of migration, which showed remarkable continuity compared to Eurasia and Africa.

“There is remarkable continuity between earlier and later skeletons with South Americans today,” said Cosimo Posth, an archaeogeneticist from the Max Planck Institute for the Science of Human History. “For example, modern-day Quechua and Aymara from the Central Andes can trace their ancestry back to the ancient people of the Cuncaicha site from 9,000 years ago onwards. This is a longer-standing continuity than you see in other continents.”

The big question right now is why the branching occurred so fast. What seems certain is that the narrative of humanity’s distribution across the Americas is far more complex than meets the eye.

“We’re very enthusiastic about the prospects for a much richer understanding of American population history, but this is still a vast region full of geographic and chronological holes,” says Reich. “We’d like to collect more genetic material from earlier and later sites and from more countries, such as Colombia, Venezuela, and other parts of Brazil. We also want to examine the evolution of genetic traits over time.”

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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

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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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