A few months ago, I posted about a possible meteor strike on Antarctica. Here it is, in the news again. The theory is, it caused the greatest extinction ever and some people propose it broke up the continents. I think this is wrong. The continents have always been quite restive since they first congealed out of the primal planetary material.
By Robert Roy BrittClick on image to enlarge
Senior Science Writer
posted: 01 June 2006
06:07 pm ET
An apparent crater as big as Ohio has been found in Antarctica. Scientists think it was carved by a space rock that caused the greatest mass extinction on Earth, 250 million years ago.
The crater, buried beneath a half-mile of ice and discovered by some serious airborne and satellite sleuthing, is more than twice as big as the one involved in the demise of the dinosaurs.
The crater's location, in the Wilkes Land region of East Antarctica, south of Australia, suggests it might have instigated the breakup of the so-called Gondwana supercontinent, which pushed Australia northward, the researchers said.
"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," said Ralph von Frese, a professor of geological sciences at Ohio State University.
If a meteor busted apart the continents this would mean they were all one unity before the strike and then fell apart. But geologists have detailed how they have moved together and apart repeatedly, cartwheeling into new configurations. After looking at various proposed maps, I would say, the cartwheeling effect is quite striking, they don't simply move away, they rotate away from each other. This infers a current within the mantle which causes them to ride in arcs rather than straight away from an impact point, for example.
Continents shifted around at far slower than a snail's pace throughout Earth's history like pieces of a puzzle, drifting together and pulling apart to form oceans, he said. Part of the eventual fascination with his idea came from globe-gazers' observation that continents such as Africa and South America look like they could fit together snugly.
Following up on Wegener and others' work, a University of North Carolina at Chapel Hill geologist believes he has discovered a new, long-vanished supercontinent. That early amalgamation of most of the world's continents in one vast land area later split up several times, reformed and divided again to begin shaping Earth's current continents.
The primeval supercontinent, which Professor John J.W. Rogers named Columbia, existed more than 1.5 billion years ago and is older than any of several giant landmasses previously proposed.
"I named the supercontinent Columbia because some of the best evidence for its existence is in the Columbia River region of western North America," Rogers said. "Starting at about 1.8 billion years ago, all of the continents existing at that time began to collide into a single land area."
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For the first half of the planet's existence, the land masses were naked to the elements. The atmosphere has gone through several revolutionary changes over the course of the planet's lifespan. It is undergoing one right now thanks to human activity.
The rate of erosion a billion years ago was ferocious. One could also assume the planet's core was hotter, too, fueling rapid changes in crust configurations. Out of a pretty toxic stew, life arose. It wasn't in a paradise but rather a very hostile environment. If we went to the earth a billion years ago, it would look like hell to us. We couldn't stay long, it would destroy our protective equipment. Life arose in the oceans. There is increasing feeling that this happened where the continental plates plunged down into the mantle. To this day, life flourished in particular where hot vents spew minerals from the mantle into the sea. These clefts are underwater rift zones. I would propose that rift zones underwater as well as on land, fuel evolution.
Meanwhile, geologists at Rice University have located the oceanic portion, off the southern African coast, of a boundary between two immense continental plates, solving a mystery that has plagued tectonic researchers for more than 35 years.
The northern boundary between the west African (Nubian) plate and the east African (Somalian) plate has long been identified as the East African Rift Valley. From the time plate tectonics was proposed in the mid-1960s, geologists have speculated about whether, and in what direction, the boundary continues from the south end of the rift valley, beyond which seismic and volcanic activity disappear.
Rice geologists Richard G. Gordon and James Lemaux II, along with geologist Jean-Yves Royer of the Institut Universitaire Européen de la Mer (France), report their findings in the April issue of the journal Geology.
Comparing records of magnetic variations in the seafloor of the southern Indian Ocean, they located the intersection of the Nubian, Somalian and Antarctic plates within a 100-kilometer-wide region known as the Andrew Bain Fracture Zone Complex. The submarine complex, located south of Africa, is more than 1,000 miles long and, at its southern end, intersects the northern boundary of the Antarctic plate.
"This boundary has been elusive because there is very slow movement between the Somalian and Nubian plates," said Gordon, the W.M. Keck Professor of Geophysics. "Both plates are moving away from Antarctica, but the Somalian plate is moving slightly slower, so the relative movement between the African plates is only about two millimeters per year."
Gordon, Royer and Lemaux, now with BP Exploration (Alaska) Inc., determined movement rates for the African plates by studying the magnetic profile of the seafloor on both sides of the slowly slipping fault zone. New seafloor is continuously created as the African plates pull away from Antarctica.
Not only has life developed first in subduction rift zones undersea, protected from the fury of the younger star called the sun, the crust recycles the organic and inorganic material of the crust over a very long time cycle. When the mantle ejects fresh material onto the surface of the planet, it feeds the organisms living there which is why the most lush farming lands are associated with recent volcanic action. This would suggest a very strong connection between the material being processed in the mantle with the creation of life forms.
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The crust that goes under a continent at subduction zones doesn't melt right away but falls through the mantle until it oozes onto the core.The crust is distinctly different from the mantle.
By Robert Roy Britt
LiveScience Managing Editor
posted: 17 May 2006
01:09 pm ET
A huge slab of folded Earth that scientists think used to be part of the ocean floor has been detected near the planet's core.
The discovery supports the theory that Earth's crust is constantly recycled deep into the planet as molten material from below simultaneously pushes up to refresh the surface.
The structure is about 125 miles deep and at least 125 miles wide and 370 miles in the north-south direction. In consistency, it is more like a giant, folding mush of taffy, researchers said today.
"If you imagine cold honey pouring onto a plate, you would see ripples and folds as it piles up and spreads out, and that's what we think we are seeing at the base of the mantle," said Alex Hutko, a graduate student University of California, Santa Cruz and lead author of a paper describing the discovery in the May 18 issue of the journal Nature.
This would seem to confirm the idea that the crust, when it plunges into the earth and drops to the core, is radically different from the mantle. And it takes a long time for the mantle to digest. We still don't understand the mechanism that causes volcanoes, if the mantle is alien to the crust in some fashion, how does it break through?
Scientists think there are deep, steady currents moving in the mantle. The core is irregularily shaped and is extremely dense and locks out both the crustal and the mantle material, it seems. This reminds me to say, the most interesting and mysterious celestial object bar none is our own planet! We should be consumed with curiousity about it! And we must understand how it works and dangers inherent to this planet's past.
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One of the interesting features of rift zones is their habitat variety. Namely, there are many levels and it goes from one extreme to the other, very hot or very cold to the opposite. Rifting also exposes many layers of the earth's past which releases many different kinds of minerals. This variety creates more distinctive niches.
Islands do this, too, of course, as Darwin showed so elegantly with his famous finch studies. But the weakness of the island approach is the very isolation which pushes genetic drift along at a tremendous pace compared to continental land masses, it also is often a dead end due to isolation. Rift valleys are not one way streets like islands.
Nor are they like the land around steep mountain ranges that isolate communities. Long ranges like the Andes effectively keeps out living things on one side from interacting in any with with creatures on the other side. But rift valleys are open to both sides. Animals and plants can move down into a rift valley or emigrate out of it but unlike a plain or water basin like the Mississippi or Amazon, they aren't part of a easily mixing community.
Life forms on the great plains and river basin jungles evolve at a fairly slow, even glacial rate. Any mutation genes will be washed out or overlaid by mating within a major population. Only if that population is suddenly terminated and the climate drastically altered, do mutations thrive. But in developing rift zones, this diversification happens much more frequently since there is semi-isolation on the steep downslopes as well as the constantly changing environment in the lowest levels due to falling well below sea level just like Death Valley or the Dead Sea, for example.
So some chimpanzee/homo erectine creatures wandering into the African Great Rift Valley could end up being cut off from the greater chimp population off in the Congo jungle drainage area. Due to this seperation, various groups of homo erectine creatures would end up mating with a much smaller pool of sex partners and thus, even small genetic ticks and glitches end up suffusing through the entire rift valley population, over a million years, leading to significant differences from the larger chimpanzee population in the great Congo river basin area.
When our most distant ancestors first split off from other mammalian groups, if one looks at probable maps of the mega continents back 100 million years ago, it is obvious that the lemur/proto-monkey groups were in the rapidly developing rift zones spreading apart India, Africa and South America. Antarctica and Australia's rifts were already filled with ocean water and uncrossable very early in the mammalian splits for of course, no mammals survived Antarctica's climate change and Australia had no mammals, changing from a rift valley host to full island isolation status.
Today, thanks to humans, there are no genetic islands. We have united the entire planet into one genetic pool which is why diversity is decreasing. This is a paradox that will haunt us in a bad way over time.