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Viewing Inside the Earth
Roland Piquepaille writes "Last week, a study released by Princeton University said that geoscientists have captured images of the interior of the Earth by using techniques similar to body scanning by physicians. This study also revealed in-depth structures which might explain how our planet is changing -- and aging. They studied more than 86,000 earthquakes which occurred since 1964. And they found 32 "mantle plumes" which are believed to cause island chains, such as the Hawaiian Islands and Iceland. They have been conjectured thirty years ago, but this is the first visual evidence they exist. This overview contains more details and references, including a rendering of mantle plumes in action."
It looks just like some scenes from The Core.
I'm really amazed how Science Fiction is able to shape and mold our understanding of real science.
I have been pwned because my
Hey man, where are all the massive geode caves, as depicted in The Core? Oh nevermind... (he could ask for anything and he asks for hot pockets and Zena *tapes*)
In other news, with the recent Slashdotting, Princeton shows they're super-smart, for not posting the recent core scans online, at 2megs a pop.
It is very cool to hear that a 30 year old theory can be turned into observation. Now if we could only do that with religion, there'd be fewer needless deaths in the world.
I wonder what this does to the hollow earth theory...
Hollow Earth Theory
I would argue that slashdot has just bought into hype surrounding one scientific paper. Seismic tomography work has been incrementally improving for many years.
Moreover, I suspect this paper will be very controversial -- the inversion of tomographic data is necessarily model-dependent, and many scientists are going to be skeptical of the claim that the have settled the source claim of plumes once and for all. [It's much easier to understand why plumes would originate at the thermal boundary at the core; what causes a plume to begin if it starts somewhere in the middle of the mantle?]
another ramp up in seismic survey was reported in this article in the san francisco chronicle.
"Stratigraphically the origin of agriculture and thermonuclear destruction will appear essentially simultaneous" -- Lee
How do we know how hot the core of the Earth
is?
We derive our primary estimate of the temperature of the deep earth from the melting behavior of iron at ultrahigh pressures. We know that the earth's core depths from 2,886 kilometers to the center at 6,371 kilometers (1,794 to 3,960 miles), is predominantly iron, with some contaminants. How? The speed of sound through the core (as measured from the velocity at which seismic waves travel across it) and the density of the core are quite similar to those seen in of iron at high pressures and temperatures, as measured in the laboratory. Iron is the only element that closely matches the seismic properties of the earth's core and is also sufficiently abundant present in sufficient abundance in the universe to make up the approximately 35 percent of the mass of the planet present in the core.
The earth's core is divided into two separate regions: the liquid outer core and the solid inner core, with the transition between the two lying at a depth of 5,156 kilometers (3,204 miles). Therefore, If we can measure the melting temperature of iron at the extreme pressure of the boundary between the inner and outer cores, then this lab temperature should reasonably closely approximate the real temperature at this liquid-solid interface. Scientists in mineral physics laboratories use lasers and high-pressure devices called diamond-anvil cells to re-create these hellish pressures and temperatures as closely as possible.
While predicition of seismic and volcanic events is still, well, progressing... Detection and tracking of such an event is very much doable...
A tsunami resulting from a seismic event can be devistating, however the landing times can be predicted... The WestCoast/Alaska Tsunami Warning Center (US specific, though I'm sure there are others..) has a page (http://wcatwc.arh.noaa.gov), that include papers, faqs, and also nice charts showing if an eartquake hit how long would it take the wave to hit (http://wcatwc.arh.noaa.gov/ttt/ttt.htm)
Volcanic eruptions also are interesting in that they tend to throw up ash detectable via satellites... On the NOAA polar orbitals, channel 4 (10.3-11.3 microns) minus channel 5 (11.5-12.5 microns) shows most plumes... A good website for more information is NESDIS's volcano page (http://www.ssd.noaa.gov/VAAC/)
- Dr. Evil
Free your ecomony and enact the FairTax
"sufficiently abundant present in sufficient abundance"
I read the headline and immediately thought, wouldn't it be great if we could map the interior of other planets, or the moon? The knowledge we have about what lies beneath the surface of Mercury, Venus and Mars seems to be mostly speculation, with no easy way of investigating. But on a body without active plate tectonics, I guess this technique wouldn't be usable at all. I suppose there are other sources of disturbance such as significant meteorite impacts, but they're much rarer than earthquakes (on Earth, anyway).
:)
Also, does this method rely on the liquid nature of the mantle? Would these acoustic waves propagate as effectively through solid rock (I guess not)? So, even if we could create the effect of an earthquake on, say, the moon, would it even help?
(should get back down to Earth, really!)
These sigs are more interesting tha
Actually it is believed that Iceland _does_ sit on top of a mantle plume as well as being on a plate boundary - the evidence is that there is apparently just too much magma being produced there to be just explained by oceanic ridge magmatism. The online article on "VOLCANOES, MANTLE PLUMES, and HOT SPOTS" linked to in the weblog mentions that hotspots can occur on plate boundaries.
It wouldn't take a lot of uranium settling to the core to form a natural nuclear reactor. I can imagine the reactor pulsing as it heats up, poisoning itself like Hanford did when they first fired it up, shutting down and cooling which allows it to shrink. Since the core is molten, the lighter fission products would convect away allowing pure uranium to accrete once again and repeating the cycle.
At the imaging resolution we're currently getting from seismographs, it's not clear to me the reactor would show up in these images. It wouldn't take a lot of "contaminates" to form a small nugget of uranium at the center of the putative iron core.
There is a growing movement in the geosciences that claims there is no evidence pointing to "mantle plumes." Everyone knows /. readers are well-balanced and open to new ideas, so in that spirit I offer up this link to the UK Geological Society.
Remember, an open mind is a terrible thing to waste.
The Apollo missions deployed seismometers on the moon and recorded over 12000 "events" from 1969-1977. There's some info in this abstract, which I found using, you guessed it, google (search term "moonquakes study interior"). Apparently most of these events are moonquakes caused by tidal forces, as opposed to plate tectonics on Earth.
I hold it, that a little rebellion, now and then, is a good thing. -- Thomas Jefferson
RTFA
Sig (appended to the end of comments you post, 120 chars)
No, we destroyed them with all our seismic noise and "Underground" atomic bomb tests.
Here is an illustration of how these mantle plumes are *moving* under ourselves (Credit: Jamie Painter, Visualization Scientist, Copyright The Regents of the University of California, Link).
This is not the "images" captured by geoscientists mentioned earlier on that page.
There really is some debate over wether this is so. 3He/4He ratios are indeed high, and this is normally attributed to a lower mantle source (possibly as deep as the core mantle boundary). HOWEVER four recent (and independent) tomography experiments image a major, strong, low-wave-speed anomaly in the upper mantle beneath Iceland that does not continue down into the lower mantle. These studies strongly suggest that iceland is fed by an upwelling originating in (and confined to) the upper mantle.
The suggested explanations for this are somewhat tenuous - that the plume gains strength in the upper mantle and is not imaged at depth runs counter to the improved tomographic resolution with depth, and besides, doesn't make much sense chemically.
Speaking as a geochemist, the real interest lies in tieing in the 3He origin with tomographic images. The evidence is rapidly shrinking for a chemically seperate 'upper' and 'lower' mantle, but rather for a 'marble cake' type mantle with small regions of primitive material mixed in with more recent 'evolved' mantle material.
I suppose this shouldn't surprise me, but the first thing I thought when I looked at the rendering was, "Gee, the interior of the earth looks like a lava lamp."
The second thing I thought, of course, was, "Well, duh."
Proud member of the Weirdo-American community.
Sure they can. I have no problem with that, however I believe the AC that replied to you above me states is pretty nicely. I believe Iceland was discussed back when I took global plate tectonics, and I was given the impression that it was not a hotspot.
The main fact that keeps me skeptical about the presence of a hotspot under Iceland is the fact that if there is one there, then the mid-Atlantic ridge has remained exactly at the same fixed point about that hotspot for a loooooooong time. Look at other hotspots around the world. With Hawaii, you can track the motion of the Pacific plate over the hotspot by the occurrence of islands and seamount. With the Yellowstone hotspot, you can track the North American plates course from the Columbia River Flood basalts.
Project Steve
Well, the easiest answer for your question is that the mid-Atlantic ridge probably isn't moving. Material is produced there, the plates themselves slide away from it, and in other areas are subducted (or subduct). So it's perfectly reasonable for the ridge to have remained in one place for a long time.
It's also possible that there's a relationship between the causes of hot spots and of the ridge itself, so that the two are moving, but move in concert.
A few random comments on this subject.
/. story is posted on the first day of the fall AGU (American Geophysical Union) meeting. I'm quite sure that there will be discussions and debate about this.
So-called hot spots (fixed volcanic positions) was first proposed by the great Canadian geophysist J. Tuzo Wilson almost 40 years ago.
The mantle plume origin of these hot spots was proposed by W. Jason Morgan (as mentioned in the Princeton link). Morgan also the put forth the first model for global plate tectonics on a sphere (spring AGU meeting, 1967). This extended the work of Wilson that looked only at transform faults.
I've known Jason for 25 years and can truly say that he is one of the nicest guy you could ever meet. He is also an incredible smart scientist.
Ironically, this
Seismic tomography has been around for over two decades. Global body-wave seismic tomography has been performed primarily since the 1990's. I did seismic tomography work about twenty years ago albeit using surface waves covering only a portion of the Earth.
I hope that they publish a resolution map of their inversion model. An error map would also be good. Many times only the final model is presented.
Bingo! Earthquake waves are the only things we know about that go through the planet. Even radio waves don't make it.
Best wishes,
Mike.
To elaborate on mikerich's reply, EM waves (e.g. x-rays) attenuate rapidly in the earth. Ground penetrating radar, for instance, can penetrate about 10 meters in good areas. Experiments have been done with extremely high-powered GPR systems, but they tend to turn the ground surface into glass (not good from an airplane). Very low frequency electric currents generated by the interaction of the earth's magnetic field with the solar wind are used in the method known as magnetotellurics. You can see down maybe 100 km, but the wavelengths are so long that the resolution is very coarse. And 100 km is still just the uppermost mantle.