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."

Comments

The Core

[CoboyNeal]

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.

seismic survey

[eyenot]

another ramp up in seismic survey was reported in this article in the san francisco chronicle.

Re:seismic survey

[eyenot]

this new research grant seems to follow pretty closely on the heels of new activity occuring at yellowstone national park, described here, here, and here (where you can also buy your own survey equipment.)

apparently, yellowstone park is right on top of a vent or something that has exploded catastrophically and according to some is overdue to do the same soon.

i'm willing to bet that the funding discussed in the article i linked to above:

Grants totaling $319 million from the National Science Foundation have been awarded to cover the first five years of the major new project, called EarthScope. Work has already begun on its array of instruments and facilities, which will provide the tools for decades of future detailed studies.

... has eveything to do with attempting to determine just how soon and how badly North America is going to be covered with ash and oochi-hot burning lava. Cool, or what?

Pictures?

[Zardoz44]

Where are they? We were told what it looked like years ago.

Offtopic sidenote...

[_Pinky_]

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/)

Shame it requires earthquakes

[CaptainAlbert]

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!) :)

Re:Shame it requires earthquakes

[Anonymous Coward]

Seismic detection equipment is very sensitive, able to detect waves beyond the ability of humans. An earthquake needs to be at least a 3 on the richter scale for people to feel it. I also believe geologists used explosives to generate seismic waves to study the earth,(search for oil).

I remember reading an article in the 80's in either Science Digest or Scientific American about how underground testing of nuclear weapons sent waves all over the planet and how some geologists were taking advantage of it to get a better picture of the core. I wonder if any nuke testing data was used in this study.

Resolution?

[jmichaelg]

To assert categorically that the core is iron strikes me as foolish. It's hard for me to believe that the density of Uranium wouldn't almost guarantee that it forms the central core of the earth. At 19,000 kg/m^3, it's almost 3 times as dense as iron. Although iron is around 30,000 times as abundant as uranium on the surface and assuming the abundance ratio didn't change much as you went down towards the core, you're still talking about a fair amount of Uranium.

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.

Re:Resolution?

[jandrese]

If this were true, wouldn't volcanos be far more radioactive than they are today? I woudn't think the uranium would make a 100% pure seperation in the core.

Besides, doesn't uranium refract sound waves differently than iron? That seems like something we could test somehow. Perhaps reading the article will be enlightening...

Re:Resolution?

[The Fun Guy]

Uranium is rarely, if ever, found in the pure metallic form. Uranium has a valence of 6, forms uranium oxides very readily, and doesn't lose the oxygen without a lot of chemical coaxing. These oxides would rarely break down under natural conditions to free up the pure metal. Uranium is indeed denser than iron, and would be expected to sink, but uranium oxides are lighter, and float up to the mantle.

Re:Resolution?

[jmichaelg]

If this were true, wouldn't volcanos be far more radioactive than they are today?

Not necessarily. I can think of two ways the radioactivity wouldn't be expressed.

1. If a uranium core is small, then a few miles of surrounding material would serve to contain the radioactivity. The heat, however, would conduct outwards and drive the lighter basalts upward.
2. The other possibility is that the transit time from the core to the surface is sufficiently long that the fission debris have completely decayed.

Lord Kelvin's estimate of the age of the earth was 100 million years based on his understanding of heat radiation and conduction. He started with a molten sphere at 7000 Kelvin and figured out how long it would take to cool to what we see today. His math was right but his estimate was wrong by a factor 45 because he didn't know about radioactive heat sources. Point being that radioactivity is already implicated in explaining why the earth is as hot as it is. The question is are the fissionable elements concentrated at the center or dispersed throughout the mantle or both? The best argument that they're dispersed is that uranium is chemically reactive and readily forms oxides which are lighter than iron. On the other hand, there isn't a lot of lab chemistry being done at the intense pressures and heat found just a few miles below our feet, let alone several thousand miles down so we don't really know how uranium chemically behaves under those conditions.

As to your refraction question - it goes back to the resolution of the tool being used and the size of a uranium core as to whether it would show up or not.

Re:Resolution?

[mikerich]

To assert categorically that the core is iron strikes me as foolish.

Actually its not, we have plenty of iron meteorites in our museums which are essentially an iron-nickel alloy. The crystallisation patterns (known as Widmanstatten patterns show that the metal cooled extremely slowly (ie. it was well insulated ie. it was at depth ie. it formed the core of a planetoid).

Uranium settling to the core would not form a reactor since natural uranium cannot sustain a chain reaction (the U238 gobbles up the neutrons) without a moderator. Even if there had been one long ago fuelled by relatively abundant U235, natural decay would have killed it by now. The 'reactor' in West Africa was moderated by ground water, which there isn't a lot of in the middle of the Earth.

And I'm sure a geochemist in the house will be able to tell me for sure. Isn't uranium partial to binding with silica - so the outer layers of the Earth are relatively enriched in uranium - it gets scarcer as you go down.

Best wishes,
Mike.

Plumes not universally accepted

[pongo000]

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.

Re:ok...

[pyr0]

"The online article on "VOLCANOES, MANTLE PLUMES, and HOT SPOTS" linked to in the weblog mentions that hotspots can occur on plate boundaries."

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.

Re:This is awesome

[ComaVN]

No, it's the kind of crap movie where the producers know it's crap, so it's declared to be a homage or parody to a pulp genre, so the fact that it's crap is actually put forward as one of its good qualities. Compare with Godzilla.

Suspension of disbelieve for me does not tolerate people drilling to the center of the earth, to do anything remotely noticable to the core.