Scientists are to sail to the mid-Atlantic to examine a massive "open wound" on the Earth's surface.
A drill will be used to extract samples of the exposed mantle
Dr Chris MacLeod, from Cardiff University, said the Earth's crust appeared to be missing across an area of several thousand square kilometres.
The hole in the crust is midway between the Cape Verde Islands and the Caribbean, on the Mid-Atlantic Ridge.
The team will survey the area, up to 5km (3 miles) under the surface, from ocean research vessel RRS James Cook.
The ship is on its inaugural voyage after being named in February.
Dr MacLeod said the hole in the Earth's crust was not unique, but was recognised as one of the most significant.
He said it was an "open wound on the surface of the Earth", where the oceanic crust, usually 6-7km thick (3.7-4.3 miles), was simply not there.
"Usually the plates are pulled apart and to fill the gap the mantle underneath has to rise up. As it comes up it starts to melt. That forms the magma," he said.
"That's the normal process. Here it has gone awry for some reason.
"The crust does not seem to be repairing itself."
Dr MacLeod said the research could lead to a "new way of understanding" the process of plate tectonics.
The scientist will test theories he developed after visiting the area in 2001 - including the possibility the missing crust was caused by a "detachment fracture".
"Effectively it's a huge rupture - one side is being pulled away from the other. It's created a rupture so big it's actually pulled the entire crust away.
A rock called serpentinite is exposed at the surface
"We also think the mantle did not melt as much as usual and that the normal amount of mantle was not produced."
As a result, the mantle is exposed to seawater, creating a rock called serpentinite.
The survey voyage, costing $1m (£510,000), will be led by marine geophysicist Professor Roger Searle, from Durham University.
Dr Bramley Murton, from the National Oceanography Centre, Southampton, is the third expert taking part.
They will set sail from Tenerife on Monday and return in April.
The team intends to use sonar to build up an image of the seafloor and then take rock cores using a robotic seabed drill developed by the British Geological Survey in conjunction with Dr MacLeod.
The progress of the voyage can be followed online.