Mountains of Evidence Suggest Human Evolution Had
Rocky Start
By Dave Mosher, LiveScience Staff Writer
posted: 19 December 2007 04:13 pm ET
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Geology may be a long-overlooked, major factor that
created conditions favoring the evolution of modern
humans.
That's the conclusion of geologists at the University
of Utah, who detail their findings in next month's
issue of the journal Geotimes.
It's fairly well-established that changing climate,
and thus vegetation, in East Africa spurred human
evolution, but there has been no agreement about what
exactly caused that change, said Royhan Gani
He thinks the riddle's answer is in rocks, and how big
slabs of it move altering continents and building
mountains by a process called tectonics.
"The idea of tectonics influencing evolution has been
discussed since at least 1983, but no one's brought it
to the foreground," said Gani, who co-authored the
study with his wife, Nahid Gani.
Rock pushups
The evidence the couple studied was in "the Wall of
Africa," a chain of highland rocks which extends for
almost 3,700 miles (5,950 kilometers) from Sudan to
South Africa. Two chunks of Earth's crust moving apart
created this expansive feature.
"You get volcanism, but mostly an upwelling of magma
pushing on the crust from below," Royhan Gani said. He
compared the action to stretching plastic over a water
spout: Where there are weaknesses in the film, the
water pushes out bubbles.
In an Ethiopian stretch of the wall, the Ganis
painstakingly mapped out the subsurface rock to show
at least 3,200 feet (1 kilometer) of uplift happened
between 3 million and 6 million years ago, creating
valleys and basins.
This local and drastic "superplume" of tectonic
activity caused the region's climatic to change,
Royhan Gani said.
"These plateaus rose up and cut off much of Africa
from wet Indian Ocean weather, sort of like the Rocky
Mountains cut off Pacific [Ocean] air," he said. "That
eventually dried up jungles into savanna and
woodland."
Evicted ancestors
Gani said anthropologists found the new work
compelling.
"Essentially, our ancestors were kicked out of trees
and evolved full bipedalism," or walking and running
on two feet, he told LiveScience. "They had to adapt
to an environment with fewer and shorter trees and
more spread-out food sources."
They also had to avoid being eaten.
"Some people argue running is a major reason our
ancestors survived," he said. "They couldn't fight
most predators face-to-face, so they fled."
Fossils indicate one of the first fully bipedal early
humans, Australopithecus anamensis, emerged about 4.1
million years ago near the region the Ganis studied
placing it smack-dab in the middle of the
jungle-to-savanna change.
In the future, Gani hopes to further investigate just
how much tectonic activity accounts for the appearance
of such early humans.
"It all happened within the right time period," he
said. "Now we need to nail it down."
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