New research mirrors a lubricating jelly layer beneath the tectonic bowl that allows them come slide. Credit: Dorling Kindersley / Getty Images

Any geologist will certainly tell girlfriend the earth’s crust is broken into tectonic plates that “float” roughly like huge rafts. However just what these rafts have actually been floating upon, has been a secret – till now.

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A team of new Zealand scientists detonated tons of dynamite and also listened for echoes to expose the underbelly the the Pacific plate. They found a 10 kilometre thick channel the lubricating jelly-like rock, which castle say permits the plate come slide above it, follow to a report in Nature.

German meteorologist Alfred Wegener proposed the idea the rafting continents ago in 1912 after ~ perusing maps and also noticing that the east coast of south America and also the west coast of Africa would certainly fit together favor jigsaw pieces. Yet scientists just started taking the idea serious in 1963 once geophysicists Fred Vine and also Drummond Matthews proved that the tardy on the ocean floor, on either side of the mid-oceanic ridges, was indeed moving.

These days plate tectonics is “obvious”, says Louis Moresi, a geologist in ~ the university of Melbourne. “You can log on come Google Earth and actually plot the movement.”

The plates themselves are composed that a special layer of tough rock recognized as the lithosphere the lies above a softer layer known as the asthenosphere. Yet no one knew what lay in ~ the lithosphere asthenosphere boundary (LAB).

In the previous geologists relied on earthquakes originating on the various other side of the world of the earth to try and find out. Like medical professionals placing a stethoscope to the earth’s surface, lock detected seismic waves.

The truth these waves relocate at different speeds through different layers enabled geologists to lay out a coarse photo of the medium through which they travelled. However natural seismic waves are 10-40 kilometer in size – too long to settle the fine-grained structure listed below the plates. So the brand-new Zealanders took matters into their own hands.

“Rather 보다 relying ~ above earthquake waves the come from listed below we create our very own ‘earthquakes’ v dynamite shots,” claims Tim Stern at Victoria University, Wellington, who led the project. The resulting waves are around 500 metres long and also able to fix finer structures. The blast zone was sited ~ above the southern guideline of brand-new Zealand’s north Island where the 73-kilometre thick Pacific key dips in ~ the Australian plate in ~ the rate of about 40 millimetres a year.

The team set up 877 Coke can-sized seismometers strung prefer beads follow me 85 kilometres. Climate from lot of boreholes lock detonated fifty percent a tonne that TNT in each.

The seismic echoes revealed something inexplicable stuck come the Pacific plate’s underbelly – a channel of jelly-like rock around 10 kilometer thick.

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Researchers used blast tide to get a watch of what lies in ~ the Pacific plate together it dives below new Zealand’s north Island. At the base of the plate they discovered a 10 kilometres thick jelly-like channel, the lithosphere asthenosphere border (LAB), i m sorry decouples that from the basic asthenosphere. Credit: Cosmos Magazine

“We always thought the boundary would be gradual and also defined by temperature. This study reflects it’s one abrupt change and requires something more than temperature alone to explain it,” says geologist Andrew Gleadow, additionally at the university of Melbourne.

The brand-new Zealand team says the jelly rock gains that is consistency indigenous a greater concentration that water or magma 보다 is present in the lithosphere over it. But it would not have to be too high. If the lithosphere contains 0.1% magma, also a 2% concentration that magma can be enough to define the consistency that the rock in the channel. “On a million-year time range this would show up weak and also jelly-like,” defines Stern.

The finding of the jelly channel can also aid resolve a 50-year debate about whether the plates relocate as a an outcome of being thrust or pulled. Very early idea was the magma gift extruded indigenous the mid-oceanic ridges was pushing the plates apart. One more pushing force could come from progressively creeping convection currents beneath the plates the act like rollers in ~ a conveyer belt.

On the various other hand the significant force can be a pulling one. Together one sheet of an oceanic bowl dives ago into the mantle in ~ – together the Pacific one is act – it traction the rest of the slab after it. The detect of the jelly layer renders the pushing and rolling mechanisms much less likely, claims Gleadow. “If the plates are mechanically disconnected indigenous the mantle below, over there can’t be good coupling to underlying convection movements.”

On the various other hand, the jelly layer adds load to the idea the gravity is the driving pressure pulling the key along. As one edge of the plate is gift dragged under, the short friction jelly layer means the rest of the plate just slithers after it like a ski top top snow.

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The following question is how this channel to be formed and if that is current all end the world, says Moresi. Evidence from vault studies ideas at a comparable structure in ~ the coastline of Norway and another off Costa Rica. If the is discovered everywhere, “it would change our expertise of the internal dynamics quite a lot”.