- Underground volcanic action on ancient
Mars sculpted gorges far larger than the Grand Canyon and melted enough
water to feed floods of biblical proportions, two geologists suggest in
a study published today.
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- Most scientists have attributed the gorges
to the bowing and stretching of the terrain from surface forces. Under
the new theory, such features were instead shaped from below by rising
wedges of molten rock known as dikes.
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- Under the theory, the dikes would have
also melted vast quantities of ice. This would explain the colossal floods
that scientists generally believe scoured Mars 2 billion to 3 billion years
ago.
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- The theory, which appeared today in the
journal Nature, was devised by geologists Dan McKenzie and Francis Nimmo
at the University of Cambridge in England.
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- Under their scenario, dikes pushed up
to within several miles of the surface, forcing the rock above to jut upward
and outward. The area in the middle sagged, forming a canyon.
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- Meanwhile, the molten rock melted ice
in the frozen ground, underground pools formed and spread and the rock
above Ø as if afloat Ø shifted into the broken, chaotic pattern
characteristic of Mars.
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- The water trapped underground could have
offered the sort of warm, moist oases where some have suggested that life
could have survived.
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- When the water ultimately found its way
to the surface, it collected in the canyons. The two geologists calculated
that such a process could have let loose floods of 400 trillion gallons
or more.
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- McKenzie argued that a gigantic dike
larger than any on Earth, or a series of smaller ones, could run beneath
the canyon network known as the Valles Marineris, the planet's best-known
landmark.
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- The Valles Marineris stretches about
2,500 miles Ø roughly the distance from New York to San Francisco
Ø and runs as deep as six miles. Its walls tower more than five
times higher than the Grand Canyon's.
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- Alfred McEwen, a geologist at the University
of Arizona, challenged the molten dike theory as a full explanation for
Mars' canyons. He said there is scant evidence that there was full-scale
volcanic activity, such as volcanoes or lava flow, at the time the gorges
took shape.
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