Plate tectonics is a hot story playing out right under our feet. Its tale describes the movement of buoyant chunks of land mass as they collide and rupture, forming the mountainous ripples, fault lines and volcanoes that encompass the earth.
The earth’s surface is in a constant state of flux. It is made up of solid sections that float on top of a sizzling hot fluid matrix called the mantle. Each 100 km thick piece of land is a tectonic plate, and each moves independently of the others, generally at a rate of several millimetres a year. Plate tectonics, the continual collisions and interactions of the terrestrial plates floating on a sea of magma, explains such natural disasters as volcanism, earthquakes, and tsunamis.
Tectonic plates slowly grind past one another, move apart, or slam shut, causing oceans to disperse and supercontinents to appear over millenia. Sometimes one plate slides beneath another, dipping into the earth’s fiery mantle and forming subduction zones. Once the plate slips into the mantle, its rocky crust begins to melt and the infamous fiery magma oozes out of the earth in a volcano.
Without tectonic drift, the earth would literally stand still and none of these natural phenomena would exist. And yet, that’s exactly the scenario proposed by a controversial new theory.
Though unlikely to occur in the near future, the theory proposes that tectonic plate movement may stop in the next 350 million years. Such an event may have also been a critical geological event in earth’s history. Presented by Dr. Paul Silver, a geophysicist at the Carnegie Institution, during the Dec. 2006 annual meeting of the American Geophysical Union, the theory is stirring up a great deal of talk.
At U of T’s department of geology, professor Pierre-Yves Robin is skeptical due to the lack of physical evidence for the theory.
“The fact is that there is no proof that plate tectonics ever stopped. There is nothing in the literature on this theory, and there is no paper [in the field of geology] that is arguing this,” said Robin.
Silver claims that the cessation of plate tectonics may have been a fundamental part of the earth’s history. From about 1.6 to 1.1 billion years ago, the massive supercontinent Rodinia formed, and plate movement and the subduction process may have stopped along with it. At that point, if the contentious theory of motionless tectonic plates is true, there would have been no tectonic natural disasters.
But when a subduction process stops in one area, another subduction zone must open up elsewhere in order to get the plates going again.
According to Paul Silver, if tectonic plates stood still for 100 million years, volcanoes would have vanished and the earth’s outer crust would have become thicker and cooler. Eventually, the mantle would begin heating up and tectonic plates, as well as volcanism, would become active again.
Another advocates of the theory is Lawford Anderson of the University of Southern California, who attributes the large strip of granite in the northern hemisphere to the melting of the mantle beneath Rodinia into the supercontinent in a massive subduction process.
Despite their arguments, however, Robin remains doubtful.
“Why would plate tectonics have to stop? There is no mechanism present, [and] there is no evidence,” Robin argued. The truth would have to be uncovered with a major reconstruction of the various openings and closings of the oceans at different times. Such an ambitious project would have to show no active subduction zones around Rodinia to prove the theory right.
“Reconstruction is an unambiguous way of reassembling various parts of land that are scattered around the earth,” explained Robin.
Without a reliable reconstruction of Rodinia, said Robin, one cannot know what really happened.
Otherwise, the only conclusive test of the theory’s veracity will come in 350 million years, when the theory predicts that tectonic plates will once again grind to a halt, proving Silver right-if anyone is around to notice.
