Earth's Major Tectonic Plates May Be Speeding Up
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The movement of Earth's major continental tectonic plates is speeding up, suggests a new study.
The study, presented at the Goldschmidt Geochemistry Conference in Sacramento California, challenges the idea that the rate of plate movement remains stable.
"This is quite mind boggling," says Professor Kent Condie of the New Mexico Institute of Mining and Technology, who led the study.
"It's different from what most people thought because Earth is cooling and everybody assumed plate movements would slow down."
Continental drift is caused by heat deep in the planet, driving the convection of material in the Earth's mantle.
The eight major and numerous minor tectonic plates on the planet's surface are moved by these convection currents.
Condie's research, which has been submitted for publication in the Precambrian Research Journal, examines how supercontinents assemble and break up.
To identify how continents have moved, Condie and colleagues looked at the geomagnetic record in the Earth's crust to see how much it has changed over time.
The researchers found the frequency with which continents have been colliding has been increasing over at least the last two billion years maybe longer.
They also found the a rate at which new supercontinents form has been increasing, and the length of time ocean basins last has been decreasing.
"All of these lines of evidence indicate plate tectonics is speeding up, not slowing down," says Condie.
Why continental drift is accelerating, however, is a mystery, says Condie.
A separate paper presented at the Goldschmidt conference led by Professor Peter Cawood of the University of St. Andrews in the United Kingdom, also suggests the rate of continental drift has changed over time.
Cawood and colleagues examined earlier studies on continental movement, finding the planet was stable between 1.7 to 0.75 billion years ago — a time known as Earth's 'middle age' — which coincides with the formation of the Rodinia supercontinent.
During this time, they found there was little new crust building activity, no major changes in atmospheric composition and few major developments in the fossil record.
In contrast, major ice ages and changes in oxygen levels occurred on either side of this period.
Cawood suggests the stability seen during the Rodinia supercontinent epoch may have been due to the gradual cooling of Earth's crust.
"Before 1.7 billion years ago, the Earth's crust would have been substantially hotter, meaning that continental plate movement may have been governed by different rules to those that operate today," says Cawood.
"[750 million years ago], the crust reached a point where it had cooled sufficiently to allow modern day plate tectonics to start working, in particular allowing subduction zones to form where one plate of the crust moves under another."
This increased activity could have kick-started a series of events, including the break-up of Rodinia and changes to levels of key elements in the atmosphere and seas.
"This in turn may have induced evolutionary changes in the life forms present at the time," says Cawood.
Article originally appeared on ABC Science Online.