The Atlantic Ocean is widening and moving the Americas to one side, Europe and Africa to the other. But it is not exactly known how.
A new study suggests that deep, beneath the earth’s crust, in a layer called the mantle, hissing hot rocks rise and press on tectonic plates – the rocky jigsaw pieces that form the earth’s crust – that meet beneath the Atlantic Ocean.
Previously, scientists thought that the continents were mostly pulled apart while the plates under the ocean moved in opposite directions and crashed into other plates and folded under gravity. But the new study suggests that this is not the whole.
The research began in 2016 when a group of researchers set off on a research vessel to the widest part of the Atlantic Ocean between South America and Africa; in other words to ‘the middle of nowhere’, said lead author Matthew Agius, who at the time was a postdoctoral researcher at the University of Southampton in the UK but is now at Roma Tre University in Italy.
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The place is not a very popular itinerary, Agius said, noting that sometimes days would pass without seeing a single other ship or plane. Interaction is limited to sometimes whales and dolphins swimming past and a fleeting signal from the ship’s Wi-Fi. Lightless nights cover the vast sea in an unobstructed view of the galaxy and stars – and it is very, very quiet, Agius said.
But this vast, empty stretch of ocean rests on an incredibly important geological site: the mid-Atlantic ridge, the planet’s largest tectonic boundary that stretches 16,093 kilometers from the North Pole to the southern tip of Africa. It is the place where the South American and North American plates move apart from the Eurasian and African plates, at a velocity of about 1.6 centimeters per year and expanding the Atlantic Ocean.
Listen to rumble
For five weeks, Agius and his team sailed over a small section of the ridge – about 1,000 km – to drop seismometers (instruments that detect seismic waves or vibrations such as earthquakes) on the seabed.
A year later, the researchers collected the seismometers.
Until now, Agius has ‘never had good images of what is happening under the sea’. Since seismic waves behave differently depending on the material through which they move, the researchers can use the data to create images so that they can look at different layers of the earth. In that year of listening, the seismometers picked up vibrations from earthquakes that propagated from different parts of the world and through the deep mantle of the earth – a layer of mostly solid, warm rock about 2,800 kilometers thick.
While the team’s original goal was to learn how the plates were born and how they age, and they really intended to study shallower depths of the earth, the researchers found evidence of a deeper phenomenon.
They found that the transition zone of the mantle – an area with a higher density that serves as a gatekeeper between the upper and lower layers of the mantle – in that area is thinner than average, which probably means that it is warmer than was normal. Agius said that the warmer temperature in the transition zone probably made an “upward” rock from the Earth’s lower mantle to the upper mantle possible.
Researchers previously thought that plates deviate mainly from each other due to a ‘pull’ at subduction zones, places where plates collide and sink one below the other and recycle material in the mantle, Agius said. So if you pull one plate on one side (and collide with another plate at a subduction zone) and pull another plate to the other side (crashes again with another plate at a subduction zone), it would rub in the middle, where the hot material rises from below to fill the resulting gap.
“This is still happening, but the ridges were thought to be an effect of the process,” he said. But their findings suggest that since subduction zones pull the plates apart, the casing under the ridges can actively help push them apart. However, it is unclear whether this process is only related to the mid-Atlantic ridge or that all the ridges around the world are experiencing the same thing, Agius said. “The trek is still there, only we now want to determine if all the reefs are also experiencing pressure.”
Push and pull
“The findings” add a piece of the puzzle to understanding the flow in the Earth’s mantle, “said Jeroen Ritsema, a professor in the Department of Earth and Environmental Sciences at the University of Michigan, who is not part of the study was not.
And although its analysis is ‘excellent’, the study is limited, he said. They only looked at a small portion of the Atlantic seabed, so it is not clear whether their findings would apply to the entire Mid-Atlantic ridge or even to other mid-ocean ridges. “It is difficult to deduce the rocks of global rocks in the earth’s mantle from only one point of view,” Ritsema told Live Sceince. “It’s like peeking through a keyhole and trying to figure out what furniture is in the living room, kitchen and bedrooms upstairs.”
In addition, there may be some other explanations for the warmer-than-normal transition zone.
This is a very “remarkable data set they have collected with great pain,” said Barbara Ramonowicz, a professor at the University of California, Berkeley’s Earth and Planetary Science Graduate School and professor emeritus of the College de France in Paris, who also not part of the study. “I have no doubt about their analysis. … I have reservations about its interpretation,” Ramonowicz told WordsSideKick. There are known plumes in the area that could be set off and heat the area, she said.
Vedran Lekic, an associate professor in the Department of Geology at the University of Maryland, who was also not involved in the study, agrees that their statement is plausible “but not the only one possible to explain the findings.” But if the findings are repeated elsewhere, it could ‘call into question our general view of ridges’, he added.
These and other similar findings could change our maps as well. About 300 million years ago, all seven continents were merged into a single supercontinent known as Pangea. Over millions of years, plates have divided the continents, creating ocean boundaries and the modern map. But the spread of the Atlantic Ocean and the contraction of the Pacific Ocean are slowly and imperceptibly aging the maps, making them increasingly inaccurate. ‘The maps will change a bit [for now] and over millions and millions of years it will change significantly, ‘Agius said.
The findings were published in the journal Nature on January 27th.
Originally published on Live Science.