Archive for Earth Sciences Forum This site is dedicated to the Earth Sciences. We are here for you to discuss issues regarding any aspect of the Earth sciences, at all levels of knowledge. Questions are welcomed, as are open scientific debates. Enjoy!!!
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Andre
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Earth solid?Earth is not really solid as in the third rock from the sun. that's a mistake that many people make, an easy assumption for geologists and planetary physisists. But this is how it appears to work:
plenty of fluids in there, it's more like a raw egg.
But the Earth is also this:
and all that is doing this:
Now for many specialities you will find that they can cope with two of the elements out of the three. But we're trying to find out what if we can think of everything.
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billiards
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Hi Andre,
You are right that the Earth is not all solid, for starters it has a fluid outer core with a viscosity similar to water, but also, over long time-scales the mantle will flow viscously. The very fact that the Earth is round teaches us that the Earth is fluid.
However, the passage of S-waves through the mantle teaches us that over shorter time scales the Earth is predominantly a solid. P-wave reflections from the inner core have long established that the centre of the Earth is solid, and of course, any sane person will testify that their homes are built on a solid crust (unless they live on a boat!).
Many people consider ice to be the solid form of water, yet over long time-scales it flows viscously and so is really a fluid; however in every day life, for pragmatic purposes, it is often reasonable to treat ice as a solid. The Solid Earth section is perhaps then a misnoma, for pragmatic purposes it seemed easier to describe the Earth as a solid, to distinguish discussion of rocks from discussion of the atmosphere.
Of course, in some problems, like for example mantle convection and plate tectonics, we should be careful with the "solid earth" label. However, a discussion of these phenomena would still be found in the "Solid Earth" forum, although this might appear confusing and somewhat contradictory, there is little else I can do, I don't want to split the forum into too many separate boards at this early stage; unless anyone can suggest a more suitable name to encompass such a broad range of topics from mineral physics to structural geology, the solid earth tag will live on.
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Baywax
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I think Andre is reflecting on the "lava lamp" effect that may explain certain extreme variations in sea level that took place at the end of the pleocene or thereabouts(?)
http://www.sciencedaily.com/releases/2001/06/010619072105.htm
This could also explain the oblong shape of our planet and perhaps the effects of the moon on tides....
The amount of geological activity earths fluidity causes by disrupting the crust could be attributed to this effect.
BTW, what are the chances of the crust slipping on all this magma??? (Yes...... shades of Hapgood..... ewwwww)
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Baywax
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Sorry if I spoke for you Andre.
I'm just rather excited about all of those humungous cycles and objects... like earth, that we're talking about.
I've got a close friend out on the prairies who says the sun is setting further north than it should be at this time of year. Is this a possibility? If it is then what would contribute to this kind of misalignment? Thanks.
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Andre
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| Baywax wrote: | Sorry if I spoke for you Andre.
I'm just rather excited about all of those humungous cycles and objects... like earth, that we're talking about.
I've got a close friend out on the prairies who says the sun is setting further north than it should be at this time of year. Is this a possibility? If it is then what would contribute to this kind of misalignment? Thanks. |
Tell your friend that he has a vivid imagination, but no. The rotation axis of the Earth, the motion of the pole, is monitored by the inch as you can see here:
The location of the spin axis wanders a little bit around in the Chander wobble.
Also there is the tilt cycle (Milankovitch) with a period of 41,000 years and your friend is probably not that old. Moreover we are cycling to the upright position which brings the sun to a lower position.
Of course there are some issues with the spin axis of the Earth in the past, forget Hapgood, that's impossible but yet:
| Quote: | Abstract
A new apparent polar wander path (APWP) from the beginning of the Paleocene (65 Ma) to the middle of the mid-Eocene (42 Ma) is shown to be correlated with polar climatic data of the same time period. Rather than applying the classical method based on analysis of site-based poles, we "stacked" the APWPs obtained from magnetostratigraphies. Magnetostratigraphies have the advantage of displaying an unbroken record of local APWPs through time and, for a magnetozone (defined as the a combination of normal and reversed polarity intervals), the instantaneous poles are synchronous. Seven magnetostratigraphies located on 4 different plates covered sufficient time to be used in the analysis. An average APWP was then determined with respect to age at the magnetozone level for the African plate, which was arbitrarily chosen as a reference frame; virtual geomagnetic poles were transferred onto the African plate using ocean kinematic Euler rotations. The calculated APWP is characterized by a loop with two main changes of direction at magnetozones 26–25 ( 61.5–56.5 Ma) and 24–22 (56.5–48.6 Ma) distinct at a 95% level of probability, and indistinct poles related to magnetozones 29–27 (65.5–61.5 Ma) and 21–19 (48.6–40.6 Ma).
We also show that the implied rapid shift of the lithosphere with respect to the geographic pole, possibly an episode of true polar wander, was coeval with the time evolution of vertebrate occurrence on Ellesmere Island (Canadian Arctic) and with the tree ring growth rate in Western Antarctica.
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Moreau M.G. et al 2007 A new global Paleocene–Eocene apparent polar wandering path loop by "stacking" magnetostratigraphies: Correlations with high latitude climatic data Earth and Planetary Science Letters
Volume 260, Issues 1-2, 15 August 2007, Pages 152-165
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Baywax
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| Andre wrote: | | Baywax wrote: | Sorry if I spoke for you Andre.
I'm just rather excited about all of those humungous cycles and objects... like earth, that we're talking about.
I've got a close friend out on the prairies who says the sun is setting further north than it should be at this time of year. Is this a possibility? If it is then what would contribute to this kind of misalignment? Thanks. |
Tell your friend that he has a vivid imagination, but no. The rotation axis of the Earth, the motion of the pole, is monitored by the inch as you can see here:
The location of the spin axis wanders a little bit around in the Chander wobble.
Also there is the tilt cycle (Milankovitch) with a period of 41,000 years and your friend is probably not that old. Moreover we are cycling to the upright position which brings the sun to a lower position.
Of course there are some issues with the spin axis of the Earth in the past, forget Hapgood, that's impossible but yet:
| Quote: | Abstract
A new apparent polar wander path (APWP) from the beginning of the Paleocene (65 Ma) to the middle of the mid-Eocene (42 Ma) is shown to be correlated with polar climatic data of the same time period. Rather than applying the classical method based on analysis of site-based poles, we "stacked" the APWPs obtained from magnetostratigraphies. Magnetostratigraphies have the advantage of displaying an unbroken record of local APWPs through time and, for a magnetozone (defined as the a combination of normal and reversed polarity intervals), the instantaneous poles are synchronous. Seven magnetostratigraphies located on 4 different plates covered sufficient time to be used in the analysis. An average APWP was then determined with respect to age at the magnetozone level for the African plate, which was arbitrarily chosen as a reference frame; virtual geomagnetic poles were transferred onto the African plate using ocean kinematic Euler rotations. The calculated APWP is characterized by a loop with two main changes of direction at magnetozones 26–25 ( 61.5–56.5 Ma) and 24–22 (56.5–48.6 Ma) distinct at a 95% level of probability, and indistinct poles related to magnetozones 29–27 (65.5–61.5 Ma) and 21–19 (48.6–40.6 Ma).
We also show that the implied rapid shift of the lithosphere with respect to the geographic pole, possibly an episode of true polar wander, was coeval with the time evolution of vertebrate occurrence on Ellesmere Island (Canadian Arctic) and with the tree ring growth rate in Western Antarctica.
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Moreau M.G. et al 2007 A new global Paleocene–Eocene apparent polar wandering path loop by "stacking" magnetostratigraphies: Correlations with high latitude climatic data Earth and Planetary Science Letters
Volume 260, Issues 1-2, 15 August 2007, Pages 152-165 |
Thanks Andre. I'll have to console my friend. Its those lonesome prairie nights drivin' a man to visit too many websites.
Excellent data you found. Do you think the lava lamp effect could skew our rotation and orbit by much?
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billiards
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By "lava lamp effect" do you mean convection? The mantle does convect, although it convects so slowly, many many orders of magnitude more slowly than the periodocity that earth spins and orbits, thus mantle convection would not have an effect on our rotation and orbit.
However, momentum transfer in the atmosphere, oceans, and fluid outer core all do have a noticeable effect on Earth's spin.
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Baywax
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| billiards wrote: | By "lava lamp effect" do you mean convection? The mantle does convect, although it convects so slowly, many many orders of magnitude more slowly than the periodocity that earth spins and orbits, thus mantle convection would not have an effect on our rotation and orbit.
However, momentum transfer in the atmosphere, oceans, and fluid outer core all do have a noticeable effect on Earth's spin. |
Very cool!
Here's what the lava lamp effect does to the ocean floor.
| Quote: | "It's a bit like pouring batter onto a hot griddle. As it hits the griddle it sets, and has to run sideways," said UC Davis geologist Charles Lesher, who is not an author on the paper.
The blobs of partially molten rock then flow along the mid-Atlantic ridge, about 90 miles (145 kilometers) below the surface. The molten rock slowly percolates upwards and eventually reaches the surface, where it "freezes" into solid crust. As the ridge pulls apart, it draws out the ends of the "V."
"This provides an explanation for the V-shaped ridges that links the surface features to the Iceland hotspot," said Lesher. |
I think I've overestimated its effect thinking it may be an assymetrical flow with cooler and more liquid spots in the magma causing an assymetical rotation and even possibly contributing to the orbital wobble. I have a feeling this is wrong.
I'm looking for a mechanism that may have knocked us off orbit slightly contributing to a warmer temperature due to a change in proximity to the sun.
The other half of the hypothesis is that the sun may have gained in temperature and radiance and cause us to warm up.
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NileQueen
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brought to our attention by cool Hans Erren,
http://www.knmi.nl/kenniscentrum/eigentrillingen-sumatra.html
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NileQueen
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| Baywax wrote: | I think Andre is reflecting on the "lava lamp" effect that may explain certain extreme variations in sea level that took place at the end of the pleocene or thereabouts(?)
http://www.sciencedaily.com/releases/2001/06/010619072105.htm
This could also explain the oblong shape of our planet and perhaps the effects of the moon on tides....
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Beeswax, oblong = rectangular. I think you mean oblate spheroid, where a sphere (earth) gets flattened at the poles and bulges at the equator a.k.a. geoid.
Here is Garret Ito's (featured in your article) homepage. He is in Hawaii.
http://www.soest.hawaii.edu/GG/FACULTY/ITO/
Interesting article Baywax, and interesting research for sure, but no pictures. I want to see what these puzzling V-shaped ridges look like that are puzzling geologists near the ridge that goes through Iceland.
Okay I found the visuals I need in a link on his publication page for 2001
Here is Garret Ito's publication page
http://www.soest.hawaii.edu/GG/FACULTY/ITO/Publications.html
I am VERY interested in how transverse faults form at the mid-
Atlantic ridge and other spreading centers.
As far as pulsating lava lamps etc. yes the mantle, asthenosphere (plastic part of the mantle) --
lithosphere = hard rocky part of earth, which is comprised of the crust plus the upper part of the mantle directly under the crust layer
asthenosphere = the plastic part of the (lower) mantle
--would convect slowly, but can we be sure there are not pockets of softer material? Can molten material from the outer core come up through channels of any sort in the mantle? BTW the magma
at "hotspots" and volcanoes is supposed to be from friction of the plate movement and not come from too deep. Much discussion is going on about mantle plumes and hotspots at http://mantleplumes.org
Can they be that sure that a supervolcano such as Yellowstone not be that deep?
| Quote: | The amount of geological activity earths fluidity causes by disrupting the crust could be attributed to this effect.
BTW, what are the chances of the crust slipping on all this magma??? (Yes...... shades of Hapgood..... ewwwww) |
Well earth is not a layer cake and it is not a jelly sandwich. 
Let's say the crust/mantle moved while the spin axis stayed in place.
How then, would you explain the Hawaiian hotspot?
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NileQueen
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| Quote: |
Public release date: 13-Aug-2007
Contact: Sofia Valleley
svalleley@esf.org
33-388-762-149
European Science Foundation
Keeping the Earth's plates oiled
Earth’s surface is a very active place; its plates are forever jiggling around, rearranging themselves into new configurations. Continents collide and mountains arise, oceans slide beneath continents and volcanoes spew. As far as we know Earth’s restless surface is unique to the planets in our solar system. So what is it that keeps Earth’s plates oiled and on the move?
Scientists think that the secret lies beneath the crust, in the slippery asthenosphere. In order for the mantle to convect and the plates to slide they require a lubricated layer. On Mars this lubrication has long since dried up, but on Earth the plates can still glide around with ease.
Beneath continents the asthenosphere appears at around 150km depth, while under oceans it can be as shallow as 60km. Above the asthenosphere lies the lithosphere: a more rigid layer that includes the crust. By 220km depth the asthenosphere comes to an end and the mantle goes back to a less flexible state. |
Hmm. Can we be sure about this?
| Quote: | What makes the asthenosphere so slippery and why does it exist on Earth but not other planets? These are some of the key questions that have puzzled Earth scientists ever since plate tectonics was discovered, but only now are the answers starting to emerge. A combination of new experimental techniques and powerful computational theory is enabling scientists to work their way through the asthenosphere atom by atom.
Björn Winker, a mineralogist at the Johann Wolfgang Goethe University in Frankfurt, Germany, believes that the key to the asthenosphere is water. “We have to have water in the asthenosphere to get it plastically deforming,” he explains. This water is no longer in its liquid state, but is bound to oxygen in crystal structures to form hydroxyl (OH-) groups instead.
The question that really interests Winkler is ‘where does the water go’? Which minerals are clinging on to their hydrogen and enabling the Earth to perform its plate tectonic dance?
Unfortunately we can’t get samples from the asthenosphere – no-one has ever managed to drill a hole deep enough. But seismic wave patterns and magma spurting out of volcanoes give us clues as to which minerals make up the majority of the asthenosphere. Winkler finds samples of these candidate minerals on the Earth’s surface and, using specialist experimental equipment, subjects them to the pressures and temperatures estimated for the asthenosphere.
The diamond anvil cell is just one of the tools his group uses. A sample is placed between two diamonds and compressed, to reach pressures of 10GPa – one million times the pressure at the Earth’s surface. When these experiments are carried out at a synchrotron, which provides extremely bright x-ray radiation, he is able to use X-ray diffraction to analyse the way the sample behaves as the pressure is ratcheted up. “It is only possible to make these measurements at a synchrotron,” says Winkler. “Laboratory x-ray sources are far too weak for such experiments.” In other experiments infra-red radiation shines through the sample and makes the O-H bonds vibrate. By measuring how much of the infra-red radiation is absorbed by the sample Winkler can estimate how much water the sample contains and whether it manages to hold onto it as the pressure increases. However, spectroscopic measurements can’t reveal everything. “They can only give you a frequency. It is like trying to figure out a car’s problems from listening to the way it rattles,” says Keith Refson, a colleague of Winkler’s who is based at the CCLRC Rutherford Appleton Laboratory near Didcot in the UK.
Afterwards Winkler and Refson use powerful computer calculations to work out what the atoms are doing and where the water might be held within the structure. “With computer models we can calculate where the sample should rattle and match the theory with experiment,” says Refson.
Already Winkler and Refson have analysed a number of minerals in this way including ‘diaspore’ and ‘clinochlore’. “It was known previously that diaspore would not survive going into the asthenosphere, but we are able to use the knowledge we have gained and apply it to other minerals,” says Winkler. Meanwhile, clinochlore was found to be good at holding onto water, but showed some interesting changes in its structure at around 8GPa. “The nature of the hydrogen bonds start to change and the layers within the structure slide,” explains Refson.
These kind of results have been invaluable for Hans Keppler, a geologist at the University of Bayreuth in Germany. He has been trying to work out why the asthenosphere exists.
Previous theories have suggested that this ‘wet’ and slippery layer exists because minerals leave their water behind them when they melt and turn into magma. “This explains why the asthenosphere appears beneath oceans, but it doesn’t explain why we have an asthenosphere beneath the continents,” says Keppler. Lava continually bubbles up at mid-ocean ridges, but continental plates don’t have an equivalent spring of constant magma. It also fails to explain why there is a lower boundary to the asthenosphere.
Instead, Keppler has been investigating water solubility in the asthenosphere. Using a loaded piston cylinder apparatus he was able to heat and pressurise mixtures of aluminium-saturated enstatite (estimated to make up around 40 percent of the asthenosphere) and water to asthenosphere values. Similar experiments were also done with olivine (thought to make up around 60 percent of the asthenosphere).
What he found was that water solubility in olivine continuously increases with temperature and pressure, whereas in aluminium-saturated enstatite the solubility reaches a distinct minimum at asthenosphere temperatures and pressures. “It means that the mantle minerals cannot contain all the water and the excess water forms a hydrous silicate melt,” says Keppler, who presenting his findings at the 1st EuroMinScI Conference in La Colle-sur-Loup, France, in March this year. The presence of even small quantities of melt in a rock in known to drastically reduce its mechanical strength.
EuroMinScI is the European Collaborative Research (EUROCORES) Programme on “European Mineral Science Initiative” developed by the European Science Foundation (ESF).
The water solubility model explains why the asthenosphere has a lower boundary and why it exists under continental and oceanic plates. Once the aluminium-saturated enstatite passes through its minimum solubility it starts to absorb water again and deeper in the mantle (at higher pressures and temperatures) the mantle becomes dry once more – creating a lower boundary.
Meanwhile, temperatures increase more slowly underneath continents, meaning that the minimum water solubility zone for aluminium-saturated enstatite is not reached until a greater depth under continents, compared to oceanic plates. (see Fig 4 from the Science paper.)
For now the jury is still out on Keppler’s new model. “It is a very elegant, but simplified model,” says Winkler. “Essentially it is based on two minerals, which is definitely not the whole story. The question is, if we refine the theory and include a greater range of minerals will it change things much?”
Some scientists are quite hostile to Keppler’s water solubility model. “It puts a lot of people out of business,” says Keppler. Nonetheless, most people agree that the theory is consistent with what is known about the asthenosphere and that it can’t be discarded. “Only more experiments and calculations can reveal the truth,” says Winkler.
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http://www.eurekalert.org/pub_releases/2007-08/esf-kte081007.php
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NileQueen
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| Quote: | Contact: Carl Marziali
marziali@usc.edu
213-740-4751
University of Southern California
Tectonic plates act like variable thermostat
Heat loss from Earth's interior depends on size and number of plates, says PNAS study
Like a quilt that loses heat between squares, the earth’s system of tectonic plates lets warmth out at every stitch.
But a new study in PNAS Early Edition finds the current blanket much improved over the leaky patchwork of 60 million years ago.
The study, appearing online the week of Aug. 13-17, shows that heat flowed out of Earth’s mantle at a high rate 60 million years ago, when small tectonic plates made up the Pacific basin.
The reason, the authors said, is that much of the heat from the mantle escapes near the ridges between newly formed plates. Those areas are thinner and allow more heat to pass.
The smaller the plates, the greater the heat loss from the mantle on which they float, said geophysicists from the University of Southern California, Johns Hopkins University and the University of Michigan at Ann Arbor.
Several small plates have more area close to the ridge – and allow more heat to pass – than one large plate, explained lead author Thorsten Becker, assistant professor of earth sciences at USC.
“When you go back 60 million years there were a bunch more smaller plates in the Pacific basin,” Becker said.
Using seafloor age reconstructions published last year, Becker and his co-authors found that heat flow out of the mantle in the last 60 million years was greater than previously estimated.
They also found that heat flow is relatively low now that the Pacific basin consists mainly of one large plate. |
There are no undersea vents or volcanoes or ridges there?
| Quote: | Becker added that variations in heat flow would not necessarily affect surface temperature, which depends on many factors, including solar activity and greenhouse gases in the atmosphere.
However, Becker said, a leaky tectonic quilt on average would lead to greater volcanic activity, earthquakes and plate movement. This would affect almost every aspect of Earth’s geography, from sea level to erosion to climate.
“There’s sort of a chain of things that follows from a good mechanical understanding of how plate tectonics works,” he said.
Like previous estimates of heat flow, the new study raises a nagging question. If heat loss for the past few billion years was comparable to Becker’s estimate, the mantle would have had to be impossibly hot at the beginning of Earth’s history.
Becker’s study, which implies an even greater rate of heat loss, shows that previous models designed to avert a “thermal catastrophe” do not work.
“A different solution to the thermal catastrophe needs to be found,” he said.
###
Becker’s co-authors were Frank Corsetti, USC associate professor of earth sciences, USC graduate student Sean Lloyd, Clint Conrad of Johns Hopkins University and Carolina Lithgow-Bertelloni of the University of Michigan at Ann Arbor.
Becker is a recipient of a National Science Foundation Early Career award.
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http://www.eurekalert.org/pub_releases/2007-08/uosc-tpa081007.php
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scpg02
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| Quote: | | If heat loss for the past few billion years was comparable to Becker’s estimate, the mantle would have had to be impossibly hot at the beginning of Earth’s history. |
But it wouldn't be a steady loss. Woudn't you have to account for the heating caused by large impacts?
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NileQueen
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And, Maggie, have they taken into account period LIPs? LIP = Large Igneous Province such as Siberian flood basalts (traps)
or Deccan traps in India, and there is one in the North Atlantic.
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scpg02
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I saw a good show that explained the Siberian traps by a large impact on the other side of the globe. Very interesting show.
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NileQueen
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Do you recall which show? Was it NOVA or discovery channel?
The flood basalts seem to coincide with major geological events (extinction boundaries) and may indeed be linked to impacts.
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billiards
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| NileQueen wrote: | | Quote: |
Public release date: 13-Aug-2007
Contact: Sofia Valleley
svalleley@esf.org
33-388-762-149
European Science Foundation
Keeping the Earth's plates oiled
Earth’s surface is a very active place; its plates are forever jiggling around, rearranging themselves into new configurations. Continents collide and mountains arise, oceans slide beneath continents and volcanoes spew. As far as we know Earth’s restless surface is unique to the planets in our solar system. So what is it that keeps Earth’s plates oiled and on the move?
Scientists think that the secret lies beneath the crust, in the slippery asthenosphere. In order for the mantle to convect and the plates to slide they require a lubricated layer. On Mars this lubrication has long since dried up, but on Earth the plates can still glide around with ease.
Beneath continents the asthenosphere appears at around 150km depth, while under oceans it can be as shallow as 60km. Above the asthenosphere lies the lithosphere: a more rigid layer that includes the crust. By 220km depth the asthenosphere comes to an end and the mantle goes back to a less flexible state. |
Hmm. Can we be sure about this?
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I don't see anything wrong with this except for the use of the word "slippy". I don't believe the asthenosphere is slippy, the lithosphere doesn't just glide over it like a puck on an ice rink, in fact it is very hard to resolve the asthenosphere to see deformation structures because it does not reflect waves back up at us. It is a low velocity zone (LVZ), which is a seismological term meaning that the zone's wavespeed is heterogeneously lower than its surroundings. LVZs tend to refract seismic energy away from the surface, therefore seismic reflection is out of the window, seismologists have to use tomographic techniques to learn about the asthenosphere which have only a limited resolution.
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scpg02
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| NileQueen wrote: | Do you recall which show? Was it NOVA or discovery channel?
The flood basalts seem to coincide with major geological events (extinction boundaries) and may indeed be linked to impacts. |
It wasn't NOVA, a good show but I rarely watch it. Probably one of the cable science channels. Might be able to dig something up with a web search. And yes extinction played a big part, may have actually been the main thrust of the original investigation.
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scpg02
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As I recall the show said the impact was so large the Earth rang like a bell. The shockwave went around the globe and met where the Siberian traps are, causing the eruption and subsequent extinction. One of these links has a graph but I haven't really looked at it.
http://news.bbc.co.uk/1/hi/sci/tech/2030075.stm
Volcanic 'flood' linked to extinction
| Quote: | A huge outpouring of molten rock 250 million years ago may have been the decisive factor in the deaths of nearly all lifeforms on the Earth at that time.
The lava that gushed out of the ground was at least twice as extensive as previously thought, a team of international researchers now reports.
Its work suggests the "volcanic flood" was a kilometre and a half deep and covered an area half the size of Australia.
Its timing coincides with the disappearance from the fossil record of up to 90% of all marine species and 70% of land vertebrates.
Researchers suspect the upwelling released vast quantities of gas into the atmosphere, rapidly changing environmental conditions and making it impossible for most lifeforms to continue.
~snip~
Some scientists strongly suspect the impact of an asteroid or comet may also have played a significant role.
American researchers have found chemical traces in rocks from the time which they believe point to an extraterrestrial collision. |
http://users.tpg.com.au/users/tps-seti/crater.html
Asteroid/Comet Impact Craters and Mass Extinctions
by Michael Paine
| Quote: | The following graph shows impact craters on Earth by age and diameter. Also shown are the main geologic boundaries involving mass extinctions (tall, bold lines), minor boundaries (thin, short lines - fewer extinctions) and the approximate timing of "flood basalt eruptions". Originally the graph only showed craters which aligned with major extinction events but it was considered better to show all craters 20km diameter or more to avoid "counting the hits and ignoring the misses". Those which appear to align with a geologic boundary are shown as dark blue diamonds. The most notable is Chicxulub at the Cretaceous/Tertiary boundary - the event that saw the extinction of the dinosaurs.
Since multiple impacts appear to be very common throughout the solar system it is expected that some of the smaller craters are associated with other major impacts, evidence of which has not been discovered or has vanished over time. For example, the Triassic/Jurassic and Jurassic/Cretaceous boundaries appear to involve multiple impacts. Craters 40km diameter or more are likely to be caused by 2km diameter asteorids or comets. Such impacts would probably result in severe global climate disruption but it takes an asteroid/comet 10km or larger to cause mass extinctions. It is estimated that such impacts occur, on average, once every 50 to 100 million years. |
And just for balance:
Link
Contemporaneous mass extinctions, continental flood basalts, and ‘impact signals’: are mantle plume-induced lithospheric gas explosions the causal link?
J. Phipps Morgan, , T. J. Reston and C. R. Ranero
Abstract
| Quote: | Contemporaneous occurrences of the geologic signals of ‘large impacts’, craton-associated continental flood basalts, and mass extinctions have occurred far too often during the past 400 Myr to be plausibly attributed to random coincidence. While there is only a 1 in 8 chance that even one synchronous large impact within the interval of a continental flood basalt and mass extinction event should have happened during this period, there is now geologic evidence of four such ‘coincidences’, implying causal links between them. The 66 Ma (K–T) evidence suggests that impacts do not trigger flood basalts, since the Deccan flood basalt had started erupting well before the Chicxulub impact event. If extraterrestrial impacts do not trigger continental flood basalt volcanism, then we are really only left with two possible resolutions to the dilemma posed by these mega-coincidences: either the reported ‘impact signals’ at the times of great mass extinctions are spurious or misleading, or – somehow – a terrestrial process linked to continental rifting and the eruption of cratonic flood basalts is sometimes able to generate the shocked quartz, microspherules, and other geologic traces commonly attributed to large extraterrestrial impacts, while also triggering a mass extinction event. Here we explore a promising mechanistic link: a large explosive carbon-rich gas release event from cratonic lithosphere, triggered by mantle plume incubation beneath cratonic lithosphere, and typically associated with the onset phase of continental rifting. Sudden CO2/CO and SO2 release into the atmosphere would provide the primary killing mechanism of the induced extinction event. Such explosive deep-lithospheric blasts could create shock waves, cavitation, and mass jet formation within the venting region that could both create and transport a sufficiently large mass of shocked crust and mantle into globally dispersive super-stratospheric trajectories. We suggest these be called ‘Verneshot’ events.
Author Keywords: mass extinctions; flood basalts; large impacts; cryptoexplosions |
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Baywax
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I found this while searching for the full explaination of the "Lava Lamp Effect".
Movement
| Quote: | | Due to the temperature difference between the Earth's surface and outer core, and the ability of the crystalline rocks at high pressure and temperature to undergo slow, creeping, viscous-like deformation over millions of years, there is a convective material circulation in the mantle. Hot material ascends as a plutonic diapir (somewhat akin to a lava lamp), perhaps from the border with the outer core (see mantle plume), while cooler (and heavier) material sinks downward. This is often in the form of large-scale lithospheric downwellings at plate boundaries called subduction zones. During the ascent the material of the mantle cools down both adiabatically and by conduction into surrounding cooler mantle. The temperature of the material falls with the pressure relief connected with the ascent, and its heat distributes itself over a larger volume. Because the temperature at which melting initiates decreases more rapidly with height than does a rising hot plume, partial melting may occur just beneath the lithosphere and causing volcanism and plutonism. |
[url]http://en.wikipedia.org/wiki/Mantle_(geology)[/url]
Mantle Plumes
Here's a good article on Mantle Plumes and it does actually mention the lava lamp effect.
| Quote: | | In this lecture we discuss hotspots and mantle plumes, the phenomena that explain why volcanoes can occur away from plate boundaries. Among the topics that will be discussed are the characteristics of hotspots and mantle plumes, the evolution of mantle plumes, and the interesting links that might be made between continental rifting, climate change, extinctions, magnetic reversals and mantle plumes. |
http://www.nipissingu.ca/faculty/ingridb/geology/hotspots.htm
Lava Lamp Plumes...
| Quote: | | Some authors (e.g., Cox & Van Arsdale, 2002) have held on to the Morgan-Crough Bermuda plume model, which would require a a pulsating (“lava lamp”) plume and/or severe control by lithospheric structure on melts rising into or erupting onto the crust. In support, Cox & Van Arsdale (2002) note that predicted Bermuda hotstpot tracks cross the ca. 65 Ma igneous activity in Mississippi, and also the ca 115 Ma activity in Kansas (Figure 2). However, there is no “LIP” (large igneous plateau) in Kansas or elsewhere that might represent the effects of a “plume head” at the beginning of the putative Bermuda plume track. Moreover, Cretaceous and Cenozoic igneous rocks elsewhere in North America (some are noted in simplified form in Figure 2) would necessarily require other plumes (McHone, 1996) [Ed: See also CAMP page]. |
http://www.mantleplumes.org/Bermuda.html
and lastly but not leastly... 
| Quote: | | What’s a lava lamp got to do with Northwest earthquakes? Visitors to the exhibit will learn that, too. |
http://www.washington.edu/burkemuseum/earthquakes/press/bigone.html
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scpg02
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| Quote: | | Lava Lamp Plumes... |
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Baywax
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That's the action!
The action of the lava lamp-like effect with denser material rising and falling inside of what her NileQueenishness has determined to be a "oblate spheroid" (earth) was considered to perhaps be the cause of the sea level rising to heights that exceed those caused by hydro and glacio-isostatic lift during the last "ice age".
Here's a time-lapse film of a lava lamp for your entertainment
http://www.youtube.com/watch?v=-Z0ne-xHlaM
The thread that thought about the geo-lava-lamp came up in is here:
http://www.physicsforums.com/archive/index.php/t-165114.html
Run away Lava...lamp...
http://www.austin-animation.flixprod.com/lava_lamp.mpg
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