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
I lost a pair of RayBans quite a long time ago. I wonder if they found them in that 4 billion year old rock?
In the 1960s oceanography came up with some surprises. First of all, it was recognized that the ocean beds were not filled with miles and miles of sediment, as would be the case if the world's rivers had been carrying silt to the oceans for four billion years. Instead it was found that the ocean floors were geologically new.
Expansion
Image: Atlantic Floor Spreading
The second surprise was the discovery of the Atlantic ridges, a series of parallel ridges which run mostly north and south throughout the Atlantic. The ridges show a series of parallel magnetic reversals of the top layers of rock, matching east and west from approximately the center of the Atlantic. Further research has found the same in the Pacific and Indian ocean, although of a more complex pattern. Geological dates of the ridges also match from the center out. The oldest ocean beds are just east of China, with smaller stretches just off the North American east coast and in the south Caribbean. These regions all date from the Jurassic era, 200 to 150 million years ago.
It looked like the Earth had indeed been expanding, and in fact it looked like there were no oceans before the Jurassic. That means the original land mass (Pangea, the single land mass which had already been suggested as the parent to all of today's continents) must have covered all of the Earth at one time. The start of ocean floor spreading (as it is called) dates from after the first appearance of the giant dinosaurs during the Jurassic.
You can look at a globe and make some simple calculations. Subtracting the estimated spread of the Atlantic and Pacific from the current circumference of the Earth (25,000 miles) gives an earlier circumference of about 12,500 miles. The Earth had roughly doubled in diameter.
Gravity is a function of the mass divided by the square of the radius of the Earth. The mass of the Earth, assuming no change in density for the new material, is a cubic function of the radius. Thus gravity is linearly proportional to the radius of the Earth. As Earth expanded, gravity increased in proportion.
bookmark, thanks for posting
Other than LAVA BASED rocks, ALL rocks are the same age!! ALL of the earth except for living things are the SAME AGE except for lava and meteors....am I wrong? Did God make newer rocks?
This is a TREMENDOUS discovery, and thanks for adding some links to "snowball Earth"/ Continental Drift stories.
Greenland being "old" does not surprise me. That Greenland has been able to preserve 3.8Byo material is astonishing!
The "Professor Moores" mentioned in this article is a pioneer in this field and is well respected. Congratulations to him and his team!
As an example from the article
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.
:') You're most welcome.
I don't think so....
Only if you see God in processes like erosion and volcanism. I do.
For a great read and pleasant introduction to historical geology I recommend "Rising from the Plains" by geology-oriented author John McPhee. While he may come a little close to environmental 'preachiness' in a few places (he's dealing with the geologist-grandson of John Muir!) he keeps it pretty balanced. The educational aspect of the book far outweighs any negatives IMO.
I think you may be astounded at how much "new rock" has been created over the past 4+ billion years!
New sedimentary rock formation is an ongoing process.
You can look at a globe and make some simple calculations. ...(snip)... the Earth (25,000 miles) gives an earlier circumference of about 12,500 miles. The Earth had roughly doubled in diameter.
In terms of geologic time; wouldn't that be a phenomenal rate of expansion? Doubling the circumference of the earth in less than 200 million years? It is almost like a slow motion explosion.
Earth Expansion Sites. (It's a theory.)
Crusty Old Discovery Reveals Early Earth's History (3.8 billion years old outer crust)
http://www.freerepublic.com/focus/news/1806290/posts
I said volcanic rock was being formed every day.
Didn't you read what I said...I excluded volcanic rock formation and meteors....otherwise all rocks are the same age.
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The Earth’s radius is about 4,000 miles (6,400 kilometers). The main layers of its interior are in descending order: crust, mantle and core.
The crust thickness averages about 18 miles (30 kilometers) under the continents, but is only about 3 miles (5 kilometers) under the oceans. It is light and brittle and can break. In fact it's fractured into more than a dozen major plates and several minor ones. It is where most earthquakes originate.
The mantle is more flexible – it flows instead of fractures. It extends down to about 1,800 miles (2,900 kilometers) below the surface.
The core consists of a solid inner core and a fluid outer core. The fluid contains iron, which, as it moves, generates the Earth’s magnetic field. The crust and upper mantle form the lithosphere, which is broken up into several plates that float on top of the hot molten mantle below.
SOURCE: LiveScience reporting
http://msnucleus.org/membership/html/jh/earth/igneous/lesson5/igneous5a.html
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IGNEOUS ROCKS |
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Only if you mean to exclude the entire sea bed (most of the earth)
Fusion At The Cores Of Planets And The Origin Of Earth's Oceans
Abstract:
The text proposes that neutrino oscillations inside planetary matter are responsible for the fabrication of new protons, neutrons and electrons. From this, hydrogen nuclei are likely to form at the core of dense rocky planets. Slow neutrons produced from the oscillation of neutrinos inside dense matter, may be fused into atoms near a planet's core. This will result in new elements production within a planet. Calculation of how many neutrino oscillations are required for new matter fabrication inside a planet is discussed. A plausible fusion process with growth of heavier elements is described via slow neutron amalgamation with atoms and standard beta decay processes which are commonly utilized in production of heavier elements in a laboratory context. Newly fabricated hydrogen is slowly brought to the surface, transiting crustal rocks and into the hydrosphere and atmosphere. A new proposal for the origin of Earth's oceans is discussed. Seven predictions are proposed which are a direct consequence of this physical geochemical model. This model illustrates that a Big Bang creation event is not required to account for observed Geo and Cosmo-chemical abundance i.e., the fabrication of hydrogen. See also my related planetary expansion paper under "Planetary Sciences" on the index page or by clicking here: http://www.johnkharms.com/planetary.htm . Also see "Solar System and Galaxy Evolution" at: http://www.johnkharms.com/solarsystem.htm .
Key Words: Neutrinos, Neutrino Oscillations, Chemistry, Big Bang, Protons, Neutrons, Electrons, Matter Fabrication, Slow Neutrons, Fusion, Ocean Water, Metallic Hydrogen
See #39.
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