The heart of the world

One of the biggest mysteries in science lies literally beneath our feet; the structure and composition of the interior of the Earth.

We have direct access only to the barest fraction of it.  The deepest borehole ever created is the Kola Superdeep Borehole, on the Kola Peninsula in Russia near the border of Norway.  It's 12.26 kilometers deep, which is pretty impressive, but when you realize that the mean radius of the Earth is just under 6,400 kilometers, it kind of puts things in perspective.

What we know is that the crust is principally silicate rock -- lower-density felsic rocks (like granite) forming the majority of the continental crust, and denser mafic rocks (like basalt) comprising the thinner oceanic crust.  Beneath that is the semisolid mantle, which makes up two-thirds of the Earth's mass.  Inside that is the outer core, thought (primarily from estimates of density) to be made up of liquid iron and nickel, and within that the inner core, a solid ball of red-hot iron and nickel.

At least that's what we thought.  All of this was determined through inference from evidence like the relative speed of different kinds of seismic waves; despite what Jules Verne would have you believe, no one has been to the center of the Earth (nor is likely to).  But figuring all this out is important not just from the standpoint of adding to our knowledge of the planet we live on, but in comprehending phenomena like magnetic field reversals -- something that would have obvious impacts on our own lives, and which are still poorly understood at best.

We just got another piece of the puzzle in the form of a paper last week in Nature that suggests our picture of the Earth's inner core as a homogeneous ball of solid iron and nickel may not be right.  Using data from seismic waves, scientists at the Australian National University in Canberra have concluded that the inner core itself has two layers.  The exact difference between the two isn't certain -- as I said before, we're limited by what information we can get long-distance -- but the best guess is that it's a difference in crystal structure, probably caused by the immense pressures at the center.

[Image courtesy of Drew Whitehouse, Hrvoje Tkalčić, and Thanh-Son Phạm]

In general, whenever a wave crosses a boundary from one medium to another, it refracts (changes angle); this is why a straw leaning in a glass of water looks like it's bent.  If the angle is shallow enough, some of the wave's energy can also reflect off the interface.  When that happens to seismic waves inside the Earth, those reflected waves bounce around inside the core; when they finally make it back out and are measured by scientists on the Earth's surface, features such as the energy, wavelength, and angle can provide a lot of information about the materials it passed through on its journey.

The authors write:

Earth’s inner core (IC), which accounts for less than 1% of the Earth’s volume, is a time capsule of our planet’s history.  As the IC grows, the latent heat and light elements released by the solidification process drive the convection of the liquid outer core, which, in turn, maintains the geodynamo.  Although the geomagnetic field might have preceded the IC’s birth5, detectable changes in the IC’s structures with depth could signify shifts in the geomagnetic field’s operation, which could have profoundly influenced the Earth’s evolution and its eco-system.  Therefore, probing the innermost part of the IC is critical to further disentangling the time capsule and understanding Earth’s evolution in the distant past.

The discovery of the Earth's hitherto-unknown center could help us to understand one of the most fundamental questions in geology; the structure of the inside of the Earth.  We still have a very long way to go, of course.  As I said, even understanding how exactly the core generates the Earth's protective magnetic field is far from achieved.  But the new research gives us a deeper comprehension of the structure of the inner core -- the red-hot heart hidden beneath the deceptively tranquil surface of our home planet. 

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Jerk analysis

Sometimes there are news stories that I have to feature here simply because they're cool.

This one came from some data collected by a mission called Swarm, consisting of three satellites which were launched in 2013 to study the Earth's magnetic field.  The mission is pretty important -- besides being critical to navigation, the magnetic field of our planet protects us from most of the cosmic particles that strike the upper atmosphere.  And -- somewhat alarmingly -- it appears we may be at the beginning of a geomagnetic pole reversal, when the magnetic field of the Earth flips for reasons still poorly understood.  (We know about 183 such pole reversals in the last 83 million years, which is about as long as we have good data for.  The oddest part is that they are anything but regular.  The shortest duration of a particular polarity was around 400 years -- and we've been in the current one for 780,000 years.)

What the current study looked at is a much more transitory phenomenon called a geomagnetic jerk, which sounds like a derogatory name for a geologist, but isn't.  Actually, it's a sort of hiccup in the magnetic field.  They were first discovered in 1978, when there was a sudden increase in the magnetic field intensity followed by an equally rapid decrease, only lasting a few days.  They can be localized geographically, too; there have been jerks that are measurable in North America and invisible in the magnetic field measured everywhere else.

The new study, released last week in Nature: Geoscience in a paper by Julien Aubert (Université de Paris) and Christopher Finlay (Technical University of Denmark) is called "Geomagnetic Jerks and Rapid Hydromagnetic Waves Focusing at Earth’s Core Surface."  It suggests that what's happening is twofold -- there's a slow convection within our metallic core that, combined with the Earth's rotation, gives rise to the magnetic field on the larger scale; but there are much more rapid, turbulent fluid motions, caused by rising blobs of hot liquid metal.  When those blobs impact the boundary between the outer core and the mantle, it results in shock waves that register on the surface as a jittering of the magnetic flux.

Simulation of the magnetic field within the Earth's core

The weirdest part is that the rising of the blobs (which would make a great title for a horror movie, wouldn't it?) begins a good twenty-five years before it registers on the surface as a jerk.  What process creates the blobs is still not understood, but this is at least a step forward.

"Swarm has made a real contribution to our research, allowing us to make detailed comparisons, in both space and time, with physical theories on the origin of these magnetic jerks," said Christopher Finlay, who co-authored the paper.  "While our findings make fascinating science, there are some real-world benefits of understanding how our magnetic field changes.  Many modern electronic devices such as smart phones, rely on our knowledge of the magnetic field for orientation information.  Being able to better forecast field changes will help with such systems."

All of which makes me wonder, however, how we're going to handle it when the overall magnetic field does its headstand, because the theory is that the field first collapses (or becomes highly erratic) before reforming with the opposite polarity.  I have this strangely hilarious mental image of people with their noses glued to the GPS on their cellphones all heading very efficiently to their destinations, and then suddenly they all start wandering off in random directions, never to be seen again.

Of course, it probably won't be nearly that much fun.

Um, I mean, "catastrophic."  "Catastrophic" is what I meant.

Anyhow, it's nice that we now have another piece of the puzzle as far as what's happening in the core of our planet, which -- as always -- turns out to be far more complex than we realized.  As far as jerks and pole reversals, we'll just have to wait to see what happens and find out if the models hold up under scrutiny.

As always.

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This week's Skeptophilia book recommendation is for any of my readers who, like me, grew up on Star Trek in any of its iterations -- The Physics of Star Trek by Lawrence Krauss.  In this delightful book, Krauss, a physicist at Arizona State University, looks into the feasibility of the canonical Star Trek technology, from the possible (the holodeck, phasers, cloaking devices) to the much less feasible (photon torpedoes, tricorders) to the probably impossible (transporters, replicators, and -- sadly -- warp drive).

Along the way you'll learn some physics, and have a lot of fun revisiting some of your favorite tropes from one of the most successful science fiction franchises ever invented, one that went far beyond the dreams of its creator, Gene Roddenberry -- one that truly went places where no one had gone before.

The state of GRACE

One of NASA's ongoing experiments is the Gravity Recovery and Climate Experiment (GRACE for short), which was launched, both literally and figuratively, in March 2002.  GRACE uses data from a pair of satellites to do detailed measurements of the Earth's gravitational field, information that can be used in such disparate fields as plate and mantle tectonics and the study of groundwater flow rates, deep ocean currents, and ice cap melting.

The data is frequently represented visually, using bulges, dips, and colors on the Earth's surface to represent various variables such as measured gravitational strength, temperature, and water salinity.  This generates images like the following:

And that's where the trouble started, because someone posted this image on the unfailingly bizarre site Godlike Productions with the caption, "This is the current shape of our planet?!!! WTF!!!  As modeled by the GRACE Gravity Data.  Planet being torn apart!"

Now, I don't know whether the original poster was a troll, or really believed that what (s)he was posting was true, but you'd think that once it was posted, there would be a Greek chorus' worth of shouts of "Are you a complete moron?  Or what?"  After all, if there really was something stretching the world into the shape depicted on the map, the folks in Australia would have something to say about it.

But no.  The vast majority of the responders thought that this, in fact, showed what the Earth really looks like, and that NASA was covering the whole thing up for their usual evil motives.

Oh, there were voices of reason, but they were the ones being shouted down.  Here are some comments that appeared, in order, after the original post.

Could it be since the moon is pulling away from Earth that it is pulling a chunk off Earth with it?

If that is really the current shape of our planet, then we are in deep shit. This is worse than anyone has thought! The moon is gonna pull a chunk off the planet. That or planet X's effect on our planet? No wonder there are so many quakes? The planet is being torn!!!

This is for real folks! This is imaged by GRACE Twin Satellites. This is so off from past projections. The planet is literally being torn apart.

This explains everything from sink holes, mass animal dies offs, weird weather, increase in quakes, oil leaks, continent movements, poles shifting etc...

Something is pulling a chunk off the planet, or the destabilization of the Arctic and Antarctica is distorting the planet.

Then, one person posted the following:

It is a GRAVITY map.  For fuck's sake.

But you don't stop a whole herd of Chickens Little that easily, because the outcry continued as if the Voice of Reason hadn't said a word:

Notice the three areas of extreme magnetic pressure and the weak area in the Indian Ocean. That is going to continue to sink and eventually break off completely, a chunk off the planet. Maybe it will become our new moon with an atmosphere to make it habitable.

None of the other planets look like that. The moon sure doesn't.

Seems to me like we are literally splitting ourselves apart.

the bible does say that the earth shall be destroyed including the heavens and a new heaven and earth shall be born or created. Maybe there is an earth being born within, black sun? Vril? Or the beast raising from the deep? Very interesting.

One person even responded directly to the Voice of Reason, implying that (s)he was the one who didn't understand:

No Duh! A gravity map also showing the current shape of our potato planet.

And on it goes:

Even the stretching effect can clearly be seen. It's starting to look like a skull?

Doesn't look normal to me.

After watching that again, I think the planet is rarely anything close to spherical. How come other planets don't look like that?

Then, we had one other person chime in who evidently has some understanding of what's going on here:

Wow.... I thought for a minute second that ultimate doom has befallen us.... Finally..... BUT, it's a gravity map. It's NOT a geophysical depiction... It's based on gravitational data. Kind of like the "hole in the ozone layer" enhancement maps. This is not the shape of the planet folks, it's the shape of the planet's gravitational plus and minuses, which change daily due to moon placement and other factors... Kind of like an mri if you will... If you remove certain colors from an mri does that mean you have removed parts of the person's brain?

Unfortunately, no real doom here. As this map will look very different on the next full moon.

But of course, the doomsayers paid no attention whatsoever.  They never do, somehow.

What gets me about all of this is how a quick internet search for "GRACE gravity survey" would have turned up websites -- several of them, in fact -- that explain what the image means.  So I've often railed against people who want to be able to talk about things like quantum mechanics without doing the hard work of learning what quantum mechanics really is; here we have people who are so catastrophically lazy that they can't even be bothered to do a search on Google before deciding whether or not Australia is being forcibly ripped off the surface of the Earth.

I don't know, folks.  I should have some sort of trenchant comment to make about all of this, but at the moment I can't think of anything to do but weep quietly into my coffee, and quote Professor Farnsworth:

Of course, if the people who think that the GRACE map actually represents the real, physical shape of the Earth are correct, I may get my wish sooner than I realize.