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Earth’s tectonic plates have doubled their speed

SO MUCH for slowing down as you age. Earth’s tectonic plates are moving faster now than at any point in the last 2 billion years, according to the latest study of plate movements. But the result is controversial, since previous work seemed to show the opposite.

Crust forming faster? <i>(Image: Alex Mustard/naturepl.com)</i>

If true, the result could be explained by another surprising recent discovery: the presence of more water within Earth’s mantle than in all of the oceans combined.

Plate tectonics is driven by the formation and destruction of oceanic crust. 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.

The planet’s inner heat powers plate tectonics. That heat is ebbing away as Earth ages, and this was expected to slow plate motion. A study last year byMartin Van Kranendonk at the University of New South Wales in Sydney, Australia, and colleagues measured elements concentrated by tectonic action in 3200 rocks from around the world, and concluded that plate motion has been slowing for 1.2 billion years.

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.

Both techniques showed plate motion has accelerated. The average rate of continental collisions, and the average speed with which the continents change latitude, has doubled over the last 2 billion years (Precambrian Research, doi.org/vbv).

“We expected to find that the average speed would be slowing down with time, but we didn’t get that. Both speeds were going up,” says Condie. “It was a surprise.”

Condie thinks the mantle’s huge store of water could explain the finding. When crust sinks back into the mantle, oceanic water gets sucked down too, and although most comes back to the surface in volcanic emissions, over the aeons the store of water in the mantle has grown vast.

Some of this water forms hydrous minerals that essentially make the mantle more runny, says Condie, speeding up the flow of rock. The effect is strong enough to overcome the stiffening of the mantle caused by the gradual cooling inside Earth, he says.

Peter Cawood at the University of St Andrews in the UK thinks the work is interesting and provocative. “The overall increase in the rate of plate motion with time seems real and believable,” he says, and could well be linked to changes in the mantle’s water content – although convincing sceptics that plates move faster now will be difficult without more data, he adds.

Van Kranendonk is not ready to change his mind. “Our paper documents a reduction in the rate and volume of crustal recycling for 1.2 billion years, supporting the idea that plate tectonics actually has been slowing down since that time,” he says.

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Unexpected Giant Exoplanet Discovered

A group of researchers from the University of Montreal  have announced the discovery of an exoplanet that is 115 light years away and surprisingly, was directly imaged. It also has one of the largest orbits of any known exoplanet. The discovery was published in The Astrophysical Journal.

Neptune is about thirty times further away from the Sun than Earth, around 4.5 billion kilometers away. That’s such a great distance, our minds can’t even comprehend it, and the distance from the Sun to Neptune doesn’t have anything on planet in the system of an M3 star, GU Psc, located 115 light years away in the constellation Pisces. The planet, GU Psc b, is ten times more massive than Jupiter and orbits its star at a colossal distance of 2000 AU. It takes the planet 80,000 Earth years to complete one full revolution. Neptune takes just under 165 years.

Exoplanets are typically washed out from the light of their parent star, forcing astronomers to rely on indirect methods of identification, based on how much of the star’s light is obstructed by the planet. However, the incredibly large orbit in this situation allowed them to image GU Psc b directly, based on the differing wavelengths between the planet and the star.

“The planets are much brighter when viewed in the infrared rather than visible light, because their surface temperature is lower than those of the stars, says Marie-Eve Naud. This is what has identified GU Psc b,” said lead author Marie-Eve Naud in a press release.

Another aspect that helped in identifying the exoplanet is that the host star is quite young, at only 100 million years old. The planets in the system haven’t had a chance to cool all the way, making them brighter and more easily detected. GU Psc is one of 90 young stars in the group AB Doradus and is the only one with a confirmed planet.

In order to determine some of the details GU Psc b, the researchers relied on theoretical models of how the planet may have formed. The wavelength of the light obtained from the planet indicates that it likely has a surface temperature of 800 °C (1472 °F). As a comparison, during the day on the equator of Mercury, temps only get up to about 427 °C (800 °F). They were able to use the age of the parent star to determine the mass, which is about 9-13 times more massive than Jupiter.

“GU b Psc is a true gift of nature. The great distance that separates it from its star makes possible a thorough study with a variety of instruments, allowing a better understanding of giant exoplanets in general,” co-author René Doyon said in the press release.

Researchers didn’t imagine they’d be able to directly image an exoplanet like GU Psc b with current technology, as it had been assumed that 100 light years would be the cutting-off point. Knowing that planets as distant as GU Psc b could be imaged directly may have opened more possibilities for researchers to look for exoplanets in locations they may have passed over before.