All rights reserved. They move at a rate of one to two inches three to five centimeters per year. Convergent Boundaries Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Share Tweet Email. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city.
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Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries. History Magazine These 3,year-old giants watched over the cemeteries of Sardinia. This crust forms where plates move apart, allowing hot, light magma to rise from the mantle below and solidify.
Where plates are being pushed together, the crust can either rise up to form mountains or one plate is shoved under the other and is sucked back into the mantle. That heat is ebbing away as Earth ages, and this was expected to slow plate motion. A study last year by Martin Van Kranendonk at the University of New South Wales in Sydney, Australia, and colleagues measured elements concentrated by tectonic action in rocks from around the world, and concluded that plate motion has been slowing for 1.
Now Kent Condie , a geochemist at the New Mexico Institute of Mining and Technology in Socorro and his colleagues have used a different approach and concluded that tectonic activity is increasing. They looked at how often new mountain belts form when tectonic plates collide with one another. They then combined these measurements with magnetic data from volcanic rocks to work out at which latitude the rocks formed and how quickly the continents had moved.
Geophysicists have discovered something startling about tectonic plates: when under extreme stress, they hit the gas and can accelerate in speed by up to 20 times. When they're about to split, the plates can move about as fast as the human fingernail grows, and that's very fast indeed as far as continental drift is concerned. Scientists from the University of Sydney, Australia, and the University of Potsdam, Germany, used a combination of seismic data and computer modelling to map the varying speed of a plate breakups, and you can view the results online.
The same principle applies to rifting continents once the connection between them has been thinned sufficiently. Essentially there's a tipping point where the connection between two continents becomes too weak to resist the forces moving in the other direction, and that's where the action speeds up to fingernail-growing levels.
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