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
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Introduction
One of the central arguments in favor of the Big Bang theory is that it explains well the chemical abundance within the Cosmos. It describes, for example, why hydrogen and helium should vastly dominate the other elements as a percentage of visible matter and, in fact, this is precisely what is observed by astronomers. Thus, hydrogen and helium make up perhaps ninety-nine percent of the ordinary visible matter in the Universe. The elements heavier than hydrogen and helium up to iron are fused supposedly in the stars as they evolve by consuming their atomic components in fusion processes. Elements heavier than iron are catastrophically fused via supernovae explosions, the terminal phase of a stars fusion cycle. This is the orthodox convention.
For those scientists who disagree fundamentally with the Big Bang occurrence, their alternative theories have had difficulty explaining the dominance of hydrogen in the Universe. Thus a key question arises: If there was no Big Bang in the distant past, how can there be so much hydrogen as observed in the Cosmos? It is the approach of this paper that neutrino oscillations may provide such a plausible alternative mechanism whereby hydrogen can be fabricated without invoking a Big Bang-type creation event.
The other possibility is that if there was a Big Bang event, vastly less hydrogen was fabricated by it. Perhaps, neutrinos which were likely to be high energy in the early Universe, "off-loaded" their energy into the early planetary-type objects fabricating hydrogen atoms. Hence, hydrogen is created in the cores of the planets causing the evolution of such objects to larger bodies. This is an ongoing process today.
Moreover, the fusion of slow neutrons which then beta decay to fabricate higher elements may take place at or near the core of a planet. Thus, the fusion of hydrogen is taking place within planets as well as stars. The common beta-decay process, provides a standard mechanism which enables nuclide to nucleus fusion at low energies and provides a fabrication pathway to heavier elements over time. Another consideration is that hydrogen is joining-up with other elements to form simple molecules such as ordinary water and hydrated minerals in the liquid outer core. This offers a different explanation of the origin of the oceans on Earth.
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We now know that there are (at least) three flavours (types) of neutrinos: the electron-neutrino, the muon-neutrino and the tau-neutrino (this last one has not been observed yet, but its existence is inferred by analogy) and their anti-particles. We do not know if neutrinos have mass since all attempts to measure their mass have failed (see neutrino experiments).
However, if neutrinos actually have mass, it does not necessarily mean that the electron neutrino has a fixed mass, the muon-neutrino has another fixed mass and the tau-neutrino yet another. It is possible that an electron-neutrino, for example, is a composite particle made up of different massive neutrino states. This might sound like a weird idea, but actually this is exactly how the different types of quarks (the constituents of all hadrons such as nucleons and other baryons or mesons) operate amongst themselves. In fact, the quarks that suffer decays are a mixed state of the quarks that have a definite mass. This property is called mixing, so it is thought that if neutrinos have mass, they too could be in a "mixed mass state".
For simplicity, we could assume that for example the electron-neutrino is made up of two mass states (which we could call 1 and 2), so if an electron-neutrino is created in some interaction (for example, in the sun) then as it travels, each of the mass states travels with a different speed. This means that the electron-neutrino travelling through space is no longer a "pure" electron-neutrino but might be partly electron-neutrino and partly muon-neutrino. As the neutrino continues to travel, the proportion of each vary with distance, so it is said that neutrinos oscillate from one state to another. If we set-up a detector along its path, it would then be possible to observe not only the interactions of the electron-neutrino but the interactions of the other component (muon-neutrino in this example). If we saw muon-neutrinos where we would only expect electron-neutrinos we would observe the phenomenon of neutrino oscillations (appearance experiment), but it could also manifest itself if we saw that some of the original neutrinos were not there any more (disappearance experiment). As one can see, it is absolutely necessary that for this property to be visible that neutrinos must have more than one mass state (that is, neutrinos must be massive and the masses of each of the mass states must be different ). The proportion in which the two mass states can mix inside each neutrino flavour is called the mixing angle and is not known. If neutrino oscillations could be observed, this would be one of the parameters (with the mass difference) that could be determined.
There are a large number of experiments trying to observe neutrino oscillations. Some rely on man-made sources like nuclear reactors or accelerators and others rely on "natural" sources such as solar neutrinos or neutrinos from cosmic-rays (otherwise known as atmospheric neutrinos). All of these nutrino oscillation experiments are complementary because they involve neutrinos of different energies travelling over differnt distances. Since we do not know what the mixing angle and the mass difference is between the neutrino species we need to try and cover as much of our "parameter" space as possible to be able to discover oscillations in the future.
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Another motivation for studying whether neutrinos have mass or not is to try and determine whether neutrinos form part of the famous dark matter problem. Astrophysicists have been observing for some time that the rotational speed of galaxies is not what they would expect if the total mass of the visible stars made up the total mass of the galaxy. The rotational velocity of the stars at the edges of galaxies is much larger than what would be expected if most of the mass of the galaxy was concentrated close to its centre (galactic rotational curves). This implies that there must be an "invisible" form of mass that goes out to the edges of galaxies forming a halo of dark matter. Calculations of the percentage of dark matter vary, but it is believed that the visible matter makes up only between 1% and 10% of the total mass of the universe. The amount of dark matter is a crucial parameter to know if we want to determine what is the future fate of the universe. If the mass of the universe is above a certain critical mass, the current expansion would eventually halt and the universe would commence an implosion into itself, resulting in a "big crunch" at some time in the distant future. If the universe is below this critical mass, then the universe would continue to expand for ever and if it was at exactly the critical mass then it would also continue to expand but at a continuously slower rate.
There are a number of candidates for this dark matter: some are astronomical objects like MACHOs (Massive Astronomical Compact Halo Objects) which are low mass stars like brown dwarves or large planets similar to Jupiter or black holes with masses of less than a solar mass, or sub-atomic particles that have yet to be discovered (like Weakly Interacting Massive Particles or WIMPS, and axions) or neutrinos with a mass of the order of 1-30 eV. It is worth noting that MACHOs have already been discovered by the MACHO and EROS collaborations by the technique of gravitational lensing, in which the image of a distant object is amplified by a massive object in the light path between the earth and the far-away object, but the number of these objects is not sufficient to explain the whole dark matter story. There are many other experiments that are searching for dark matter and links to these experiments can be found through the UK dark matter search site .
It is well known that there is a cosmic microwave background that permeates the universe with an average temperature of 2.726 K. The observed universe shows rather clumpy features (large voids and areas of the universe with clusters of galaxies) and the uniformity of the microwave background in the universe seemed at odds with this clumpy structure. The Cosmic Observatory Background Explorer satellite (COBE) was launched to search for ripples in the microwave background that would be compatible with the clumpiness of the observed universe. The discovery of these ripples was made in 1992, in which it was found that the temperature of the microwave background varied by differences of about one thousandth of a degree in different parts of the sky. This was a triumph for the Big Bang theory of the universe, since it verified that the origin of the microwave background was in effect the remnant radiation from that Big Bang after cooling for more than 10 billion years and that these ripples formed the density fluctuations needed to form the large scale structure of the universe. Models that explain these fluctuations include the dark matter, and the COBE data favours a model in which there is a 70% cold dark matter (objects like MACHOS, WIMPS and axions which travel at non-relativistic speeds) and a 30% hot dark matter (like neutrinos which are relativistic particles) component. This still leaves the possibility open that neutrinos could make up about 30% of the dark matter. A logical candidate could be the tau-neutrino which could possibly be the heaviest of the neutrinos (assuming a mass-heierchy amongst neutrinos). This is one of the main motivations in the search for muon to tau-neutrino oscillations at experiments like NOMAD and CHORUS.
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From Australia
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Not mentioned is that Ray Davis also discovered the solar neutrino deficit, a problem that was solved in the last few years by scientists here at Penn. The reason why Prof. Davis's neutrino experiment in the Homestake gold mine only detected 1/3 as many neutrinos as predicted by the standard solar model is that the electron-type neutrinos produced by the sun transform into muon-type and tau-type neutrinos in-flight on their way from the sun. This in turn demonstrates that neutrinos have mass. Since Prof. Davis's experiment was only sensitive to electron-type neutrinos, he saw an apparent deficit.
With little more than a tank of dry cleaning fluid--carbon tetrachloride--he discovered a fundamental fact about the most elementary particles in the universe.
Sloan Digital Sky Survey: Dark Energy, Inflation, & Neutrino Mass News
Cool, got to watch out for those neutrons, 'specially the slow ones.
Interesting description of the formation of planets like Earth, bookmark'd the link
Good Link, interesting stuff.
Interesting, thanks for the ping.
thanks for the links, if you don't hear from me for a while it's because I have a lot of reading to do!
Thanks for the link. I knew it was a theory and an interesting one too. Great gif!
I reckon you have. It might take me the next nine months to read the links you've laid down here. Bookmarked.
The Deep Hot Biosphere : The Myth of Fossil Fuels (Paperback)
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Thanks E.
oh, and...
Small Comets and Our Origins
University of Iowa | circa 1999 | Louis A. Frank
Posted on 10/20/2004 2:13:25 AM EDT by SunkenCiv
http://www.freerepublic.com/focus/f-bloggers/1250694/posts
Life on other PlanetsHighly oxidized iron is abundant on Mars, and very small-grained magnetite can then be expected to be one of the accumulated residues of microbial processes; so can iron sulfide and methane-derived carbonates. Polycyclic aromatic hydrocarbons are the large molecules that might remain in a rock that originally contained crude oil but then was exposed for millions of years to the high vacuum of space. All these substances have been found in the discovery meteorite, closely packaged to each other, and this by itself would make a strong case for the microbial interpretation. In addition, there are small objects seen under scanning electron microscopy that may well be fossils of microbes. While the last item by itself would not be conclusive evidence, the combination of this together with oil and the three residue products make a strong case for the microbial explanation. It is true that each step can occur without biological intervention, but the chance of finding by chance the evidence for all three solids in a small volume, together with hydrocarbons, seems to be very low. Many terrestrial oil and gas wells show just such an association (but an association with helium also, which the meteorite could not have transported through space).
by Thomas Gold
May 1997Earth's Oxygen EnigmaScientists have long believed that blue-green algae arose 3.5 billion years ago, pumping out oxygen and causing the oceans to fill with rust. Over the next billion years the algae transformed Earth's atmosphere, allowing oxygen-breathing life to evolve. Carrine Blank of Washington University in St. Louis... compared genetic sequences from 53 different groups of bacteria -- including blue-green algae, also known as cyanobacteria -- to construct a detailed family tree. The results confounded her expectations. "Cyanobacteria arose fairly late, about 2.2 or 2.3 billion years ago. That explains why we see this very sudden increase in oxygen, around 2.2 to 2 billion years ago, which has always been a big mystery," she says. The finding implies that something else caused the ocean rusting.
by Kathy A. Svitil
February 11, 2003
Carrine Blank of Washington University in St. Louis
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