Posted on 03/23/2007 11:06:03 PM PDT by Ernest_at_the_Beach
A sliver of four-billion-year-old sea floor has offered a glimpse into the inner workings of an adolescent Earth.
The baked and twisted rocks, now part of Greenland, show the earliest evidence of plate tectonics, colossal movements of the planet's outer shell.
Until now, researchers were unable to say when the process, which explains how oceans and continents form, began.
The unique find, described in the journal Science, shows the movements started soon after the planet formed.
"Since the plate tectonic paradigm is the framework in which we interpret all modern-day geology, it is important to know how far back in time it operated," said Professor Minik Rosing of the University of Copenhagen and one of the authors of the paper.
Sea floor is not normally preserved for more than 200 million years 
Minik Rosing
Professor John Valley, a geologist at the University of Wisconsin, Madison described the work as "significant" and "exciting".
"If these observations are substantiated it will be a significant line of new evidence indicating that plate tectonics was active and familiar as early as 3.8 billion years ago," he said.
"That really is an important conclusion."
Crack and spread
Plate tectonics is a geological theory used to explain the observed large-scale motions of the Earth's surface.
The relatively thin outer shell of the planet is composed of two layers: the lithosphere and the asthenosphere.
Ancient pillow lavas are preserved in exquisite detail
The lithosphere - made up of the outer crust and the top-most layer of the underlying mantle - is broken up into huge plates; seven major plates and several smaller ones.
These float above the asthenosphere and move in relation to one another.
Today, oceanic crust is created at plate boundaries known as mid-ocean ridges, where magma rises from the asthenospehere through cracks in the ocean floor, cools and spreads away.
As it moves away from the spreading centre towards the edges of the oceans it becomes cooler, denser and eventually starts to sink back into the mantle to be recycled.
"Sea floor is not normally preserved for more than 200 million years," said Professor Rosing.
Most is destroyed at subduction zones, such as those found along the edge of the Pacific Ocean, where oceanic crust plunges under the buoyant and long-lived continental crust.
Water world
However, in certain circumstances, fragments of the sea floor known as ophiloites are preserved when they are scraped on to the land.
This exceptional process typically occurs when continental crust begins to be sucked into a subduction zone, clogging the system.
"It goes down into the subduction zone until the buoyancy of the continent arrests the process of subduction," explained Eldridge Moores, emeritus professor of geology at the University of California, Davis.
You can actually recognise features that formed in a couple of minutes, 3.8 billion years ago
Minik Rosing
"The continent then pops back up, preserving a little bit of the overriding wedge of oceanic crust and mantle that was on the overriding plate."
Ophiolites are found today in Cyprus and Oman and show a distinctive structure.
At their base, crystalline rocks preserve the top layer of the mantle. Above, "fossilised" magma chambers give way to a layer of stacked vertical pipes, known as sheeted dykes.
These represent the conduits through which magma is extruded onto the sea floor as pillow lavas, bulbous lobes of basaltic rock that form when lava cools quickly in contact with water.
Racing rocks
The rocks analysed in Greenland are found in an area known as the Isua Belt, a zone of intensely deformed rocks in the southwest of the island that geologists have pored over for decades.
The ophiolite structure was mapped between outcrops covering 4-5km (2.5-3 miles) and shows the correct sequence of layers found in an ophiolite, except the lowest mantle portion.
"You can actually recognise features that formed in a couple of minutes, 3.8 billion years ago - a quarter of all time - and you can actually go and touch them with your hand," said Professor Rosing.
The rocks are found in the Isua Belt, in southwest Greenland
Crucially, they show well preserved sheeted dykes and pillow lavas, clear evidence to many that these are the ancient remains of sea floor created by processes seen today.
"What this tells you unequivocally is that the process of sea-floor spreading that we observe today appears to be present in one of, if not the, oldest sequence of rocks on Earth," said Professor Moores. "That is a significant milestone."
In particular, it pushes back the oldest known evidence of plate tectonics by at least 1.3 billion years and gives scientists clues to the processes that formed the surface of the Earth today.
Although the structures and processes that led to their formation would be similar to the modern era, they would not be exactly the same.
The young Earth was much hotter than now, and as it shed heat, it put many of the tectonic processes into overdrive.
"If you had plate tectonics you probably would have had more plates, moving faster, and they probably would have been thinner," said Professor Moores.
The rate of recycling of oceanic crust would therefore have been even quicker than today, making the fact that the rocks in Isua are preserved at all even more extraordinary.
"These fragments are extremely rare," said Professor Rosing. "It's just very exciting when you get one of these glimpses when you can look back nearly four billion years in time."
PLATE TECTONICS
Magma rises from the asthenospehere at mid-ocean ridges
New crust cools and spreads away from ridge
Denser oceanic crust begins to sink back into the mantle at subduction zone
Melting of slab creates volcanoes on overlying continental crust
May I suggest you also read
No Free Lunch, Part 1:
A Critique of Thomas Gold's Claims for Abiotic Oil
http://www.fromthewilderness.com/free/ww3/102104_no_free_pt1.shtml
No Free Lunch, Part 2:
If abiotic oil exists, where is it?
http://www.fromthewilderness.com/free/ww3/011205_no_free_pt2.shtml
When comet Halley came by during 1988 the Europeans (NOT nasa) took close up pictures of it. They saw a black part that was much bigger than what they thought the comet should be. They discovered a surprise: the comet was 4 times bigger in size than they had thought. That meant it was 4 cubed times more massive, or about 64 times.
It was black because it was covered with a dirty, tar-like material. Their sensors found it was "kerogen", CH2.5 polymer, which is something like oil shale.
Ridiculous. Neutrinos can't form baryons spontaneously; it violates several conservation laws. But even if we assume they can, they can't do it unless their energies are greater than 1 GeV (the mass of the neutron) in principle, but in practice the energy would have to be much greater than that, because it has to be above 1 GeV in the rest frame of the collision, not in the Earth's frame. But that last point I also waive.
The fact of the matter is that the flux of neutrinos with energies greater than 1 GeV is vanishingly small. That excludes any neutrinos from any star or supernova, or even relics from the Big Bang. All that is left are a fraction of the neutrinos from Active Galactic Nuclei. Think about how little light the Earth receives from AGNs, and you'll have a rough idea of how few neutrinos that comprises.
But how much energy would we need? Well, these...individuals...are claiming that MOST of the mass of the Earth came from this process, so let's suppose that all of it was created this way. Since the neutrinos aren't enough, let's suppose that every erg the Earth receives from the Sun gets converted to energy.
The Earth has a mass of 6x1024 Kg. That translates to 5.4x1041 Joules of energy.
The Earth receives 2x1017 Watts from the sun. A Watt is one Joule per second.
That would take 2.7x1024 seconds.
There are 3x107 seconds in a year.
Therefore, it would take 9x1016 years to build an Earth this way. The universe is 1.4x1010 years old. So it would take six million universe lifetimes to build up the Earth in this way, but that's if you use the total output of the sun. (Or rather, a series of ones like it. A star like that only lasts 10 billion years.) If you're depending on high-energy neutrinos, it will take gigantically longer.
D'oh! I meant converted to matter.
Early Water on Earth
Geotimes | February 2003 | Salma Monani
Posted on 02/09/2003 7:22:57 PM EST by CalConservative
http://www.freerepublic.com/focus/f-news/839466/posts
Early Earth Likely Had Continents, Was Habitable, According To New Study
University of Colorado at Boulder | 2005-11-18 | University of Colorado at Boulder
Posted on 11/18/2005 11:32:59 PM EST by dila813
http://www.freerepublic.com/focus/f-news/1525001/posts
Crusty Old Discovery Reveals Early Earth’s History
(3.8 billion years old outer crust)
LiveScience.com on yahoo | 3/24/07 | Robert Roy Britt
Posted on 03/24/2007 10:40:45 PM EDT by NormsRevenge
http://www.freerepublic.com/focus/f-news/1806290/posts
Diamonds Tell Story Of Earth’s Beginning
The Telegraph (UK) | 8-22-2007 | Roger Highfield
Posted on 08/22/2007 9:48:58 PM EDT by blam
http://www.freerepublic.com/focus/f-news/1885157/posts
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Just updating the GGG info, not sending a general distribution. |
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