Mountain Range's Collapse May Have Supercharged Evolution

Carlos Ganade de Araujo. What is now a plain in north-east Brazil hides evidence of a mountain range the size of the Himalayas

A mountain range the height and length of the Himalayas spurred the diversification of life when the first unambiguously multicellular organisms appeared, according to new research published in Nature.

An Australian-Brazilian collaboration have found evidence of a range, known as the West Gondwanaland Orogeny, that ran from Algeria to Togo and then in into Brazil—at the time, joining up with west Africa.

"Just like the Himalayas, this range was eroded intensely because it was so huge. As the sediments washed into the oceans they provided the perfect nutrients for life to flourish," said Professor Daniela Rubatto of the Australian National University. "Scientists have speculated that such a large mountain range must have been feeding the oceans because of the way life thrived and ocean chemistry changed at this time, and finally we have found it." Erosion of subsequent mountain ranges have been associated with similar biological effects.

Mountains, Rubatto says, “Are like icebergs, there is more beneath the surface than above, and the taller the mountain the deeper the roots.” At the base of an enormous mountain, the forces are extraordinary, producing rocks called ultra-high pressure eclogites that cannot form in other ways. As the ranges erode, some of these eclogites reach the surface.

Dr. Ganade de Araujo of the University of Sao Paulo recognized eclogites dotted across 2,300 kilometers, and with Rubatto showed they all formed at the same time, presumably from a single event. Rubatto says that since the paper was submitted, they have found rocks in southern Brazil that may also be related, extending the range's length even further. 

“The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth,” the authors note.

The 600 million year old range Rubatto has helped identify is the oldest one of this size known. Mountain ranges on this scale have come and gone since, prompting debate about why we haven't found signs of anything from the first seven-eighths of Earth's history. "There were mountain ranges before this of course,” says Rubatto, "But we've found nothing to indicate they had such deep roots. That these rocks are hard to find could be part of it, but there is also discussion as to whether the differences in the Earth's crust prevented the formation of such high mountains.”

The orogeny runs almost perpendicular to the line where, hundreds of millions of years later, Africa and South America broke apart, and was driven by the collision of previously separate continents that fused together to create Gondwana. The continent survived the merger into Pangea and the break-up before finally separating along current boundaries 130 million years ago.

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