|
Harald Franzen Scientific American
Ideas
about continental movement, earthquakes, volcanism and even
climate change need to be rethought, according to two Canadian
earth scientists. In a study published today in Nature,
they claim that huge plumes of hot rock are floating upward
from the earth's liquid core, profoundly influencing what
happens on the surface.
"In
effect we have found that the solid earth is being churned
by a four-piston heat engine with two immense sinking cold
slabs and two equally large rising hot plumes," Alessandro
Forte of the University of Western Ontario says. Measuring
earthquake waves that travel deep inside the planet, the
scientists were able to retrieve images of what goes on
inside the earth's mantle at a depth of about 3,000 kilometers.
They noticed that the waves traveled faster in two vast
arc-shaped regions under the margins of the Pacific Ocean
(blue in the illustration), while they slowed down in two
equally large plume-shaped regions below the central pacific
and Africa (red).
Whereas
current scientific belief holds that the "slow"
regions have been stagnant since the earth was formed, Forte
and his colleague Jerry Mitrovica of the University of Toronto
believe that they are actually rising to the surface, while
the "faster" portions, containing heavy material,
are sinking toward the core. As proof, the researchers cite
tiny variations in the earth's rotation and gravity field,
as well as deflections of continental regions like southern
Africa—now one kilometer higher than northern Africa.
Plate
tectonics theory does not draw a link between movements
of the continental plates and processes taking place deep
inside the earth, a view that Forte and Mitrovica hope will
be overturned by their findings. "It's a road map for
resolving a contentious debate that has hampered global
earth science since the plate tectonics revolution,"
Mitrovica says.
|
