Earth's crust wobbles like dessert over long timescales

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Washington, April 9 : An analysis of the Earth's crust has suggested that over long timescales, it wobbles like a dessert, proving that the continental plates are not completely rigid after all.

According to a report by Discovery News, the top few kilometers of the Earth's crust - the rocky lithosphere, stays strong and rigid, while beneath that, the crust is more fluid, just like the dessert's wobbly egg custard layer.

Scientists determine that when viewed on very long timescales, the Earth's crust can behave with surprising fluidity.

It may be that sometimes the crust behaves as if its plates are rigid and strong all the way down, with only the underlying mantle showing any jelly-like elasticity.

But on longer timescales, the same area of crust can act more like pudding, with only the top few kilometers, the rocky lithosphere, staying consistently strong and rigid.

"We're tying to take a new look at an old problem," said Dr Wayne Thatcher, a geologist with the US Geological Survey (USGS).

According to Thatcher, "I think of the lithosphere as ice on a pond. The thicker a patch of ice, the wider and gentler it will dip in response to weight, such as a truck driving over it,"

If the ice is replaced with a lithosphere in that analogy and the truck for mountain ranges, a basic picture of the structure underground can be arrived at.

"We tried to use different kinds of loads to probe different properties of the lithosphere," said Thatcher.

His findings determined that mountains are one load that the crust responds to on the scale of tens of millions of years.

Other loads are glaciers, which grow and shrink on a mid-range timescale of hundreds to tens of thousands of years.

Briefest of all loads are earthquakes, which trigger adjustments in the crust on the scale of just days, weeks and months.

But at the glacial timescale, the mantle behaves more like jelly, effectively limiting the more rigid 'ice' to just the crust.

Finally, on the mountain-load timescales of millions of years, only the upper crust really behaves rigidly, making for the thinnest 'ice', which bows the most under the weight of a truck.

"It turns out that what happens on the short term and what happens on the million-year timescale is different," said Thatcher.

ANI

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