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17 May 2016

The earth’s mantle is bouncing ten times faster than scientists realised

The layer beneath the earth's crust is moving in unexpected ways, which could have implications for everything from the oil and gas industry to climate change. 

By Zayani Bhatt

Scientists have known that the earth’s crust is made up of layers since 1909. Since then, earthquakes, volcanic activity, and the formation of mountains has been attributed to the shifting of tectonic plates just below the surface.  

According to a new study from the University of Cambridge, however, it may not be that simple. The earth’s mantle, the layer of magma between the earth’s crust and its core, moves ten times faster than previously imagined, causing the earth’s crust to effectively bounce up and down. The implications of this discovery could affect the oil and gas industry, our current views on global warming, and our knowledge of seismic activity and the changing face of the world’s surface.

The mantle is a 1,864 mile layer of hot rocks and solid silicate that floats just beneath the earth’s crust and above its molten core. It’s known to move up and down slightly thanks to a process of convection, wherein heat from the earth’s interior travels up and slowly lifts it, creating a wave that travels around the earth. It was thought that this movement was rare, and therefore had little to no effect on the earth’s surface. However, a database of information on the mantle’s movements collected as part of the study shows that the currents are not 10,000km from top to bottom, as originally believed, but 1,000km in size.

These shorter currents have more power, subsequently moving faster, pushing or pulling the earth’s crust further from or closer to the core. Over a period of a million years (the standard time measurement in geology) the earth’s crust can move by hundreds of metres. This means our planet is much more dynamic and is evolving far faster than previously thought.

The scientists measured the variations in depth of water at 2,120 points along the ocean floor by analysing surveys on previous seismic activity in each area. By comparing the crust’s thickness to its age, the researchers also discovered that Hawaii is one place where the volcanic activity is not due to the movement of tectonic plates, but rather the crust’s vertical movements.

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The team also created a mathematical model to describe their findings; more specifically the way changes in the temperature of the mantle affect the movement of the crust. Movement of the surface also has implications for ocean water circulation. As lead author Mark Hoggard from the University of Cambridge told the International Business Times:

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“For example, the Gulf Stream runs from Mexico to the North Atlantic, and comes back on itself deeper in the water. But, when the topography of the surface is higher, it blocks off the Gulf Stream.”

Oceanic circulation and water currents determine the climate in many regions of the earth. The Gulf Stream makes the waters around the UK much more temperate. If it were to be blocked, the temperature of our waters could change significantly – and have impact on the land too.

This study, although the first to be conducted, is still small and plenty more is to be done. Its results could have far-reaching effects in a number of different industries. For the oil and gas sector for example, changes in mantle flow dictate sediment shift and therefore how quickly hydrocarbons are generated.

The research could also help us understand the melting of the ice caps during the ice age and so provide a basis for identifying climate change today. Perhaps one day, the information could be added to models of earthquake, volcano and tsunami activity, helping to predict and prepare for these natural disasters. Until then, it’s a fascinating glimpse into the world below our feet.