AprilÊ26, 2001. Copyright, 2001, University of Western Ontario. All rights reserved


A ÒFOUR-PISTON HEAT ENGINEÓ DRIVES EARTH FROM THE INSIDE, NEW STUDY SHOWS

LONDON, ONTARIO April 26: DEEP beneath EarthÕs surface, continent-sized plumes of hot rock are floating upwards, providing a driving force for such phenomena as the movements of whole continents, earthquakes, volcanoes, and even climate change, according to a new theory by two earth scientists in Ontario.

In a paper appearing in Nature (April 26), lead author Alessandro Forte of The University of Western Ontario and co-author Jerry Mitrovica of the University of Toronto provide an answer to the longstanding mystery of how the entire Earth, from the deep interior to the surface, is changing over time.

Their work, which draws together results from many disciplines in the earth sciences, shows how a heat engine is slowly churning deep within the planetÕs interior and provides the most comprehensive model to date that explains physical phenomena occurring at the surface.

ÒIn 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,Ó says Forte, professor in the Department of Earth Sciences in WesternÕs Faculty of Science. ÒIt really ignites the imagination to realize how things are changing hundreds of kilometres beneath your feet and how this change connects to majestic features on EarthÕs surface.Ó

ÒThis find allows us to move well beyond the drift of continents described by plate tectonics,Ó says Mitrovica, University of TorontoÕs J. Tuzo Wilson Professor in Geophysics. The plate tectonics theory, proposed in the 1960s, suggests EarthÕs crust is split up into a few immense plates that constantly shift and produce earthquakes, but it does not explain how this movement is linked to processes occurring deep inside the planet, says Forte.

ÒThe first clues to finding that link appeared in the 1980s when earth scientists obtained images of EarthÕs internal structure using earthquake waves which travel deep inside the planet,Ó says Mitrovica. ÒThis method is similar to medical CAT-scanning used to image the human body. The remarkable images of the mantle, a region below the crust which extends down 3,000 kilometres to the top of EarthÕs molten core, turned earth science on its head.Ó

The images showed that deep below the margins of the Pacific Ocean are two vast arc-shaped regions where earthquake waves travel faster, while deep below the central Pacific and below Africa are two equally enormous plume-shaped regions where earthquake waves are slowed down. Because the edge of the Pacific is ringed by zones where cold, dense portions of tectonic plates descend into Earth, the ÒfasterÓ regions were clearly marking areas where slabs of heavy material were sinking into Earth toward the iron core.

A popular view held by earth scientists is that the ÒslowÓ regions are simply immense stagnant blobs of material that have remained essentially unaltered since the formation of Earth. Now Forte and Mitrovica have proven that these towering features are actually floating up toward the surface like hot air balloons. Their proof is based on a diverse array of observations ranging from incredibly small variations in EarthÕs rotation and gravity field to dramatic deflections of continental regions such as southern Africa, which now sits 1,000 metres higher than north Africa.

The pairÕs multidisciplinary approach is being hailed as the most unified model to date for the Earth dynamics and one which provides a framework for modelling long-term changes in sea-level, topography and climate. The model may also be used to further understanding of other planets in our solar system, such as Venus, Mars and Mercury, says Forte. ÒWe have discovered something grandiose in size and yet remarkably simple and symmetric.Ó

ÒItÕs a road map for resolving a contentious debate that has hampered global earth science since the plate tectonics revolution,Ó says Mitrovica.
/ENDS