- The tectonic plates among the Americas, Europe and Africa are being pushed apart as the Atlantic Ocean expands year by year.
- New research reveals what pushes the plates apart: Material from deep inside the earth erupts upward at a submarine reef in the middle of the Atlantic Ocean.
- Visit Business Insider’s homepage for more stories.
The Atlantic Ocean grows 1.5 centimeters wider every year.
This is because the tectonic plates that underlie America separate from those under Europe and Africa. But exactly how and why this happens was a mystery to scientists, as the geological forces that usually push plates apart are not common in the Atlantic Ocean.
A study released Wednesday finally answers that question. The research, published in the journal Nature, suggests that the key to the expansion of the Atlantic Ocean lies beneath a vast underwater mountain range in the middle of the ocean.
This set of underwater peaks is known as the Mid-Atlantic ridge, and it separates the North American plate from the Eurasian plate and the South American plate from the African plate. The researchers behind the study found that material from deep inside the earth rises below the Mid-Atlantic ridge to the surface, thus pushing the plates apart on either side of the gorge.
The Atlantic Ocean floor spreads
The mid-Atlantic ridge, seen in deep orange, on a NASA Earth Observatory bathmetry map.
NASA Earth Observatory maps by Joshua Stevens, using data from Sandwell, D. et al. (2014)
Imagine the earth as a chocolate truffle – a viscous center in a hard shell.
The center consists of a semi-solid 1800-mile mantle that surrounds a super-warm core. The top layer of the truffle – only about 21 kilometers thick – is the earth’s crust, which is fragmented into tectonic plates that fit together like a jigsaw puzzle. These plates surf on top of the mantle and move around as warmer, less dense material rises from deep in the earth to the crust, and colder, denser material sinks to the core. This process, known as convection, usually occurs when two plates collide with one subject, or sink under another.
In general, any upward outflow of material below tectonic boundaries such as the Mid-Atlantic Rig usually starts from a part of the mantle very close to the earth’s surface, about 3 km below the crust. Material of the lower mantle, the part closest to the core, is usually not crust-cracked.
But the new study found that the Mid-Atlantic Ridge is a hotspot for convection.
The researchers measured geological activity over a length of 621 miles. They dropped 39 seismometers under the waves in 2016 and then left them for a year to collect earthquake data around the world. Seismic waves echoing through material in the Earth’s core have prompted scientists to look into the mantle beneath the Mid-Atlantic reef.
The part of the Mid-Atlantic Ridge where researchers from the University of Southampton used earthquake measuring instruments in 2016.
University of Southampton
The group found that magma and rock could move their way to the surface there from 410 miles below the crust. The waste of material is the distribution of the tectonic plates – and the continents above – at a rate of 4 centimeters per year.
“Swell from the bottom to the top mantle and up to the surface is usually associated with localized places on Earth, such as Iceland, Hawaii and Yellowstone, and not with mid-ocean ridges,” said Matthew Aguis, a seismologist at Roma . Tre University and a co-author of the new study, Insider said. “That’s what makes this result exciting because it was completely unexpected.”
Often, material trying to move from the bottom to the top mantle is obstructed by a band of dense rock, known as the mantle transition zone, between 255 miles and 410 miles below our feet.
But Agius and his colleagues estimated that below the Mid-Atlantic Ridge, temperatures in the deepest part of the transition zone were higher than expected, making the zone thinner in the area. Therefore, material can rise more easily there on the seabed than in other parts of the earth.
Solving a geological mystery
One of the remote seismometers deployed by scientists from the University of Southampton in the Atlantic Ocean.
University of Southampton
The discovery helps solve a long-standing geological mystery.
Scientists have known that oceans expand and contract at different rates. They also knew that plates move most clearly apart at subduction zones, which usually occur on active continental edges – where the boundary between a continent and the ocean is also a tectonic plate boundary. Therefore, the Pacific Ocean expands faster than the Atlantic Ocean: most of the Pacific Ocean sits on top of one tectonic plate, and its boundaries align almost perfectly with the continental on the east and west sides, the North American and Eurasian plates. . Subduction at these boundaries causes the earthquakes and volcanic eruptions that characterize the region’s aptly named “Ring of Fire.”
However, the Atlantic Ocean sits on top of four large plates with boundaries that do not correspond to the continental boundaries – the boundaries occur in the middle of the ocean. Scientists were therefore delighted with how its seabed had expanded.
But new research suggests that building up material deep out of the mantle may be the car of the Atlantic expansion.
Catherine Rychert, a geophysicist at the University of Southampton and co-author of the new study, said this process began 200 million years ago. But one day, the rate of expansion may accelerate.
“The rate is likely to remain the same during our lifetime. It is likely to change over millions of years because it has fluctuated in the past,” Rychert told Insider.