Scientists have long known that the Earth's mantle -- the layer of our planet between its core and the crust on which we live -- contained plumes of hot rock. What hasn't been so clear is whether those plumes were related to surface hot spots and if they connected all the way down to the border between the core and mantle -- a spot 1,800 miles (2,900 kilometers) deep.
Now, thanks to a 3D map that came from a supercomputer simulation at the Department of Energy's National Energy Research Scientific Computing Center (NERSC) at the Lawrence Berkeley National Laboratory, scientists know that the plumes do indeed connect -- and that they have two gigantic blobs of hot rock deep inside the Earth as their common source.
"No one has seen before these stark columnar objects that are contiguous all the way from the bottom of the mantle to the upper part of the mantle," said Scott French, a computational scientist at NERSC and first author on a paper describing the work that was published this month in the journal Nature.
Before this research, some seismologists believed the hotspots that create surface volcanoes on Earth were shallow pools of hot rock, says a report from Berkeley News. Now the researchers know that the rock that leads to volcanoes and island formation comes directly from a fountain of sorts that starts at the border between our mantle and crust, travels 1,800 miles through the mantle and fans out as it reaches the surface, creating underground chambers of molten rock known as hot spots.
The computer simulation that created the map used the seismic waves generated by 273 earthquakes that rocked our planet over the course of 20 years. Berkeley News says that those waves served much in the same way X-rays do in a CT scan -- they helped the researchers see inside our planet. The computation that crunched data from all those quakes and the sensors that measured them took a total of 3 million CPU hours, although parallel computing -- a method in which lots of calculations are carried out simultaneously rather than sequentially -- reduced the time frame to a mere two weeks.
The lakes of hot rock at the core/mantle boundary to which all plumes were traced each measure about 3,100 miles (5,000 kilometers) in diameter. They're located directly across from each other -- one under Africa and one under the Pacific Ocean -- and the researchers estimate that they've been in the same place for 250 million years.
In addition to identifying the sources of the plumes, which are about 752 degrees Fahrenheit hotter than the surrounding rock, the 3D map showed that below about 621 miles (about 1,000 kilometers), the plumes in the mantle measure between 373 miles and 621 miles across (roughly between 600 kilometers and 1,000 kilometers), which is up to five times wider than previously thought.