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
fyi
Ancient Rocks Show How Young Earth Avoided Becoming Giant Snowball
YEC INTREP
WOW!
Actually, that conclusion presupposes that there was a Gondwanaland in the first place.Fossil Mantle Plume Under South America"The conduit appears to have remained geographically fixed with respect to the overlying continent despite thousands of kilometers of South American plate motion. This observation runs contrary to a major tenet of plate tectonic theory -- that the motion of lithospheric plates is essentially independent of flow in the upper mantle beneath the plates -- and implies that the upper mantle and the overlying South American continent have remained coupled since the breakup of the Gondwanaland super-continent and opening of the South Atlantic Ocean some 120 million years ago.
by William Corliss
But What About The Hawaiian Volcanic Chain?P.D. Ihinger is challenging the well-entrenched "Hawaiian-volcanic-chain" theory. For example, the Hawaiian volcanoes do not line up exactly. There are dozens of short, overlapping segments rather than a continuous trace across the Pacific basin. On the map, you will also see a sharp dog-leg in the trace. Further, the volcanoes Mauna Loa and Mauna Kea, only 40 kilometers apart, disgorge lavas that are distinctly different.
by William Corliss
Researchers Suggest Answer to Geological PuzzleSMU geologists Rebecca Ghent and Douglas Oliver studied the location of the major hot spots and determined that a disproportionate number occur at latitudes between 20 and 30 degrees north and south of the equator. Their observation became much more significant when the hot spots were weighted according to the amount of volcanic material that they produced. Statistical analysis shows that the likelihood of this distribution arising by chance is less than one percent... Oliver and Ghent said their observation may shed light on other geological phenomena, such as the development of superplumes, which are clusters of mantle plumes arriving together at the Earth's surface. Scientists believe that massive superplume events are responsible for some of the major changes that have occurred on the Earth, such as the breakup of the supercontinent known as Pangea into the present continents.
National Science Foundation
The Earth Is Expanding And We Don't Know Why"The geological and geophysical implications of such Earth expansion are so profound that most geologists and geophysicists shy away from them. In order to fit with the reconstruction that seems to be required, the volume of the Earth was only 51 per cent of its present value, and the surface area 64 per cent of that of the present day, 200 million years ago. Established theory says that the Earth's interior is stable, an inner core of nickel iron surrounded by an outer layer that behaves like a fluid. Perhaps we are completely wrong and the inner core is in some state nobody has yet imagined, a state that is undergoing a transition from a high-density state to a lower density state, and pushing out the crust, the skin of the Earth, as it expands."
by William R. Corliss
Science Frontiers #37
Jan-Feb 1985
(Owen, Hugh; "The Earth Is Expanding and We Don't Know Why, "New Scientist, p. 27, November 22, 1984.)
Please FREEPMAIL me if you want on or off the
"Gods, Graves, Glyphs" PING list or GGG weekly digest
-- Archaeology/Anthropology/Ancient Cultures/Artifacts/Antiquities, etc.
Gods, Graves, Glyphs (alpha order)
Now that is serious...more so than Global warming...are we causing this expansion with our constant drilling looking for oil?
I think the problem is all the laser beans in use in CD players, computers, and the like.
http://www.agu.org/meetings/fm04/fm04-sessions/fm04_U33A.html
The Tarim APWP Paradox
Gilder, S -- Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
Cogne, J -- Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
Courtillot, V -- Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
Chen, Y -- Universite d'Orleans, BP6749, Orleans, 45067 France
Gomez, J -- Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
Central Asia boasts one of the world's densest regions sampled for paleomagnetic data thanks to numerous sections of well-exposed rocks possessing stable remanent magnetizations. Such is the case for the Tarim craton, which is represented by a quasi-continuous time sequence of paleomagnetic poles since the Permo-Carboniferous. Most of these poles are derived from studies demonstrating positive fold and-or reversal tests, with N equal to or greater than 6 sites or 50 samples. Samples collected from Permo-Carboniferous rocks usually have reverse polarities, and samples collected from Cretaceous rocks usually have normal polarities, consistent with the geomagnetic polarity time scale. Despite the apparent excellent quality of the paleomagnetic data from Tarim, they impose geologically unrealistic tectonic displacements when compared to the Eurasian and-or Indian APWPs. This leads to the Tarim APWP paradox: is there a problem (inclination shallowing, overprinting, etc.) with the plentiful Tarim data, or is the Eurasian APWP not representative of the land east of the Ural Mountains? If the latter is true, then previous tectonic reconstructions must be reconsidered. If the former is true, then when/how can we rely on the paleomagnetic data? We present arguments showing that both scenarios have their pros and cons.
How Did Glacial Deposits Form 600 Million Years Ago?Dr. David Pollard, research associate, Penn State College of Earth and Mineral Sciences' Environmental Institute, and James K. Kasting, professor of geosciences at Penn State, believe that glacial deposits that formed on tropical land areas around 600 million years ago could only have formed after the Earth's oceans were entirely covered by thick sea ice. Ice can accumulate in the tropics only if temperatures are below freezing or around freezing with large amounts of snowfall. Tropical glaciers exist today only on high mountain peaks such as the Andes and Mt. Kilimanjaro, and do not reach anywhere near sea level. As the earth cools, the oceans begin freezing. The high reflectivity of the snow and ice that covers the northern and southern oceans reflects, rather than absorbs, the sun's heat and further cools the planet. The researchers conclude that it is unlikely that tropical sea level glacial deposits formed before the collapse into snowball Earth. However, having them form after the oceans freeze also seemed problematic because once the oceans are frozen, the rates of precipitation decrease drastically, to only a few millimeters per year.
Freeze-fry from the snowball EarthOn Dec. 14, Daniel Schrag of Harvard University] presented recent observations in favor of the snowball Earth at the American Geophysical Union’s meeting in San Francisco, which lasted from Dec. 12–17...
by Christina Reed
But some scientists still remain skeptical. During a presentation at the AGU meeting, Gregory Jenkins of Pennsylvania State University supported what is called the high obliquity hypothesis over the snowball Earth hypothesis. Jenkins argued that climatic conditions during the Neoproterozoic resulted from a severe tilt of Earth on its axis, possibly caused by the impact of the planetoid that formed the moon. Although a tilted Earth may have cooled the equator and warmed the poles, the theory is still hotly debated as an explanation because it seems to require low-latitude cooling prior to Neoproterozoic glacial events.
Schrag and others defend the snowball Earth theory, saying it brings context to mysteries that have plagued the geological community for decades. It explains how glaciers survived in the tropics, how iron-rich rock emerged in an oxygen-enriched world and how warm-water carbonate rocks found themselves perched atop glacial deposits. It may even explain the explosion of life in the Cambrian.
[P]aleomagnetism specialist Joe Kirschvink of Caltech linked the effect a frozen Earth would have on the hydrological cycle to a buildup of volcanic carbon dioxide. If ice covered the oceans to the equator, it would block off evaporation, dry up the clouds and deny water the chance to erode the land. Carbon dioxide would build up in the atmosphere instead of being washed out by rain and carried back to the oceans as carbonates from land. With enough carbon dioxide, the "snowball Earth" would then become a hothouse, Kirschvink said in a 1992 paper published in the book The Proterozoic Biosphere.
In 1992, Kenneth Caldeira of Lawrence Livermore National Laboratory and James F. Kasting of Pennsylvania State University calculated that the amount of carbon dioxide needed to reverse the snowball effect would be 350 times present-day levels. With a global average of 50°C below zero, Earth would bake under extreme global warming to 40–50°C in only a few thousand years.
Scientists Poke Holes in 'Snowball Earth' HypothesisFrank Corsetti of USC, a co-author on the study, said "this is the first real evidence that substantial photosynthesis occurred in the Earth's oceans during the extreme ice age 700 million years ago, which is a challenge for the snowball theory."
National Science Foundation
Press Release 05-173
September 29, 2005
The evidence does not prove large parts of the ocean remained free of sheet ice during the pre-Cambrian glaciation. Although unlikely, Olcott said it is possible one of the tiny "refugia" under the "Snowball Earth" hypothesis allowed such marine life to exist.
But, she said, "finding the one anomalous spot would be quite unlikely," adding that the samples she studied came from an extensive formation of rocks with similar characteristics.
"At what point does an enormous refugium become open ocean?" she asked.
Laser beans ? Is that a new brand from Bush's ?
:')
Welcome to FR! If we manage to bring over everyone from there, we'll add, well, okay, maybe a couple of dozen... ;') Nice beginning to your profile page!
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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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
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