Relics of a lost planet

It took astronomers a good long while to figure out how the Moon formed.

Some initial working models were found, upon analysis to... well, not work.  One early idea was that what is now the Moon sheared away from the Earth while it was molten because of centrifugal force, but the viscosity of molten rock is too high (or the rotational speed of the Earth is way too low) for that to be feasible.  Another possibility was the gravitational capture of a pre-formed body, but that makes it hard to explain the Moon's nearly perfect circular orbit.  (Captured objects -- a likely candidate is Neptune's moon Nereid -- tend to have highly elliptical orbits and/or orbits not parallel to their host planet's rotation, because there's no reason to suppose that their capture occurred at any particular angle.)

A big clue came from isotopic analysis of lunar rocks, which found that the ratios of isotopes for several different elements were nearly identical to terrestrial rocks, arguing for a common source.  The prevailing theory is that the Moon formed when, about 4.5 billion years ago, the proto-Earth was struck by a Mars-sized planet -- named Theia, after the Greek Titan who was the mother of Selene, the goddess of the Moon -- which caused a blob of material to shear away, propelling it into orbit where it coalesced into what we see today on a clear night.

Artist's depiction of the collision between Theia and the proto-Earth [Image is in the Public Domain courtesy of NASA/JPL]

The reason the topic comes up is because of a paper that appeared this week in Nature that I found out about from a friend and loyal reader of Skeptophilia.  A team led by geophysicist Qian Yuan of Arizona State University took a look at two large low-velocity provinces (LLVPs) in the Earth's lower mantle -- dense regions where seismic waves slow down, and which are hypothesized to have a significantly higher iron oxide content than the rest of the mantle -- and their models support the astonishing idea that these are the remnants of Theia.

It's wild that there are still relics discernible, between the violence of the collision and the fact that 4.5 billion years have passed since it happened.  You'd think this would be plenty enough time to stir the mantle and homogenize the material Theia brought in with whatever was present in the proto-Earth.  But Yuan et al. think that the collision's energy was mostly dissipated into the upper mantle, allowing the remnants of Theia's core to sink into the lower mantle without mixing completely -- where the pieces are still detectable today.

Like all good science, the Yuan et al. paper raises some interesting questions, such as what effect the collision had on the rest of Earth's evolution.  "A logical consequence of the idea that the LLVPs are remnants of Theia is that they are very ancient," said Paul Asimow, of the California Institute of Technology and senior author of the paper, in an interview with Science Daily.  "It makes sense, therefore, to investigate next what consequences they had for Earth's earliest evolution, such as the onset of subduction before conditions were suitable for modern-style plate tectonics, the formation of the first continents, and the origin of the very oldest surviving terrestrial minerals."

So that's today's cool scientific research, which I can say without fear of contradiction is pretty close to earthshattering.  Think about that next time you see our companion's ghostly white light in the night sky -- that despite its tranquil appearance, it may well have been born from a collision of almost unimaginable violence, billions of years ago.

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Reversing the core

I get really frustrated with science news reporting sometimes.

I mean, on the one hand, it's better that laypeople get exposed to science somehow, instead of the usual fare of the mainstream media, which is mostly stories about seriously depressing political stuff and the latest antics of celebrities.  But there's a problem with science reporting, and it's the combination of a lack of depth in understanding by the reporters, and a more deliberate desire to create clickbaity headlines and suck people in.

Take, for example, the perfectly legitimate (although not universally accepted) piece of research that appeared on January 23 in Nature Geoscience, suggesting that the Earth's inner core oscillates in its rotational speed with respect to the rest of the planet -- first going a little faster, then slowing a bit until its rotational rate matches Earth's angular velocity, then slowing further so the rest of the planet for a time outruns the core.  Then it speeds up, and does the whole thing in reverse.  The reason -- again, if it actually happens, which is still a matter of discussion amongst the experts -- is that the speed-up/slowdown occurs because of a combination of friction with the outer core, the effects of the magnetic field, and the pull of gravity from the massive mantle that lies outside it.

[Image licensed under the Creative Commons CharlesC, Earth cutaway, CC BY-SA 3.0]

That's not how this story got reported, though.  I've now seen it several times in different mainstream media, and universally, they claim that what's happening is that the inner core has stopped, and started to spin the other way -- i.e. the inner core is now rotating once a day, but in the opposite direction from the rest of the Earth.

This is flat-out impossible.  Let's start with the fact that the inner core has a mass of about 110,000,000,000,000,000,000,000 kilograms.  A mass that huge, spinning on its axis once a day, has a stupendous amount of angular momentum.  To stop the rotation of that humongous ball of nickel and iron would take an unimaginable amount of torque, and that's not even counting overcoming the drag that would be exerted by the outer core as you tried to make the inner core slow down.  (I could calculate how much, but it's just another huge number and in any case I don't feel like it, so suffice it to say it's "a shitload of torque.")  Then, to accelerate it so it's rotating at its original rate but in the opposite direction would take that much torque again.

Where's the energy coming from to do all that?

Here, the fault partly lies with the scientists; they did use the words "reversing direction" in their press release, but what they meant was "reversing direction with respect to the motion of the rest of the Earth."  I get that relative motion can be confusing to visualize -- but giving people the impression that something has stopped the inner core of the Earth and started it rotating in the opposite direction gives new meaning to "inaccurate reporting."

Worse still, I'm already seeing the woo-woos latch onto this and claim that it's a sign of the apocalypse, that the Evil Scientists™ are somehow doing this deliberately to destroy the Earth, that it's gonna make the magnetic field collapse and trigger a mass extinction, and that it's why the climate has been so bonkers lately.  (Anything but blame our rampant fossil fuel use, apparently.)  Notwithstanding that if you read the actual paper, you'll find that (1) whatever this phenomenon is, it's been going on for ages, (2) it represents a really small shift in the inner core's angular velocity, and (3) it probably won't have any major effects on we ordinary human beings.  After all, (4) the scientists have only recently figured out it's happening, and (5) not all of them believe it is happening.

So let's just all calm down a bit, okay?

In any case, I'd really appreciate it if the people reporting science stories in the mainstream media would actually read the damn papers they're reporting on.  It'd make the job of us skeptics a hell of a lot easier.  Thanks bunches.

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I felt the earth move under my feet

Some of you probably recall the highly scientific 1990 nature documentary Tremors, wherein Kevin Bacon has to battle gigantic worms that can tunnel through rock, and which have evolved such sophisticated sensory organs that they can feel your footsteps and follow you until an opportune moment to pop up and eat you for lunch, yet are still stupid enough to die from running into the wall of an aqueduct or launching themselves out of a cliff face in the fashion of Wile E. Coyote being shot from the barrel of an Acme E-Z Cannon.

The reason this comes up is because of a piece of research in the journal Geology, which I can confidently assert would have reminded no one else in the entire world of Tremors, but I'm not responsible for how my brain works, and I figure if on some level you didn't enjoy free association, you wouldn't be here.  Anyhow, the paper is titled "Eruption Risks from Covert Silicic Magma Bodies," which as you can tell from the title has zero to do with giant carnivorous worms, but does have to do with the fact that there seem to be dangerous and undetected pockets of magma underground that can be located by their seismic traces.

(See the connection?  See?  The tagline for Tremors is "They say there's nothing new under the sun, but under the ground...".  I rest my case.)

What spurred the four geologists who wrote the paper -- Shane M. Rooyakkers, John Stix, and Kim Berlo (of McGill University), Maurizio Petrelli (of Università degli Studi di Perugia), and Freysteinn Sigmundsson (of the University of Iceland - Reykjavík) -- were three instances of what they euphemistically call "Unintentional encounters with silicic magma at ~2-2.5 km. in depth," which is science-speak for some people at a drill site looking into the hole and then yelling, "FUCKING HELL WE JUST HIT A MAGMA CHAMBER."  The three sites were on Krafla (in Iceland), Menengai (in Kenya), and Kilauea (in Hawaii), and in each case was a shock because the areas had been studied extensively and the magma chambers they hit hadn't previously been detected.

Magma chambers are usually found by their seismic properties; the sound waves from explosions, and the pressure waves from earthquakes, travel at a different speed in solids than they do in liquids, so by comparing how long it took for those waves to arrive at detectors in different locations, you can infer how much of the intervening material is liquid and how much is solid.  (That's a vast oversimplification, but the gist of it, anyhow.)  Given how good this technique is, geologists thought they had all of the near-surface magma chambers pinpointed, so it was a significant shock to find out that there were some out there that we didn't know about.

Another piece of this that raised red flags for me was that word "silicic" in the title.  Magma usually comes in two flavors, mafic and felsic (or silicic).  Mafic magma is high in magnesium and iron, hardens into dark-colored rocks like basalt, and when it's molten it's highly fluid, like the rivers of lava you probably think of when you picture a volcano.  Felsic magma is high in silica and feldspar, hardens into light-colored rocks like granite and rhyolite, and is very viscous and thick when it's molten -- so volcanoes powered by a felsic magma chamber often build up so much pressure beneath that blob of sticky glop that when they erupt, it's explosive.  (Examples are Vesuvius, Mount Saint Helens, and La Soufrière -- currently erupting on the island of Saint Vincent.)

So an undetected near-surface magma chamber filled with felsic/silicic magma is not good news.  People are walking around without realizing it on top of what amounts to a giant superheated bomb.

The 1980 eruption of Mount Saint Helens [Image is in the Public Domain courtesy of NASA]

"In traditional approaches to volcano monitoring, a lot of emphasis is placed on knowing where magma is and which magma bodies are active," said study lead author Shane Rooyakkers, in an interview with Science Daily.  "Krafla is one of the most intensely-monitored and instrumented volcanoes in the world.  They've thrown everything but the kitchen sink at it in terms of geophysics.  And yet we still didn't know there was this rhyolitic magma body sitting at just two kilometers' depth that's capable of producing a hazardous eruption...  So the concern in this case would be that you have a shallow rhyolitic magma that you don't know about, so it hasn't been considered in hazards planning.  If it's hit by new magma moving up, you might have a much more explosive eruption than you were anticipating."

Which is a lot worse than a bunch of giant carnivorous earthworms.

Anyhow, that's our unsettling piece of scientific research for today.  The good news is that it's not like these magma chambers are scattered about everywhere; they still seem to occur only near active volcanoes.  So it's not like an eruption is likely to take place in the middle of Newark, or anything, which is kind of a shame, because an erupting volcano in Newark would probably be considered urban renewal.  But you never know.  Even Kevin Bacon got taken off guard by what's underground.

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This week's Skeptophilia book recommendation is pure fun: Arik Kershenbaum's The Zoologist's Guide to the Galaxy: What Animals on Earth Reveal About Aliens and Ourselves.  Kershenbaum tackles a question that has fascinated me for quite some time; is evolution constrained?  By which I mean, are the patterns you see in most animals on Earth -- aerobic cellular respiration, bilateral symmetry, a central information processing system/brain, sensory organs sensitive to light, sound, and chemicals, and sexual reproduction -- such strong evolutionary drivers that they are likely to be found in alien organisms?

Kershenbaum, who is a zoologist at the University of Cambridge, looks at how our environment (and the changes thereof over geological history) shaped our physiology, and which of those features would likely appear in species on different alien worlds.  In this fantastically entertaining book, he considers what we know about animals on Earth -- including some extremely odd ones -- and uses that to speculate about what we might find when we finally do make contact (or, at the very least, detect signs of life on an exoplanet using our earthbound telescopes).

It's a wonderfully fun read, and if you're fascinated with the idea that we might not be alone in the universe but still think of aliens as the Star Trek-style humans with body paint, rubber noses, and funny accents, this book is for you.  You'll never look at the night sky the same way again.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]

Moonstruck

A lot of times, it's the simple, easily-stated questions that are the hardest to answer.

Take, for example, the question of how the Moon formed.  Satellites around planets are common -- Jupiter has 79, for example -- but our own is a bit of an anomaly.  For example, if you make a list of moons in the Solar System in order of mass with respect to its host planet, the Earth's Moon is way out in front.  Its mass is 0.0123 of the Earth's.  Next in line would be Titan, which has a moon mass to planet mass ratio fifty times smaller (0.000237).

It's easy to picture a planet the size of Jupiter or Saturn gravitationally capturing blobs of the coalescing matter during the Solar System's formation, but it's harder to see a small planet like the Earth having the gravitational oomph to snag something the size of the Moon.  Another oddity is that of the sixteen most massive moons in the Solar System, the Moon's orbit around the Earth is by far the most eccentric.  Eccentricity is a number between zero and one that indicates how elliptical an orbit is, with 0.000 eccentricity being a perfect circle.  The Moon's deviation from a circular orbit is twice the next contender (which is once again Titan; whether that's a coincidence or not isn't known).  But the elliptical nature of the Moon's orbit is why its apparent size from Earth fluctuates, and explains why when there's a solar eclipse, sometimes it's total (complete coverage of the Sun's disk) and sometimes it's annular (occurs when the Moon is farther away and has a smaller apparent size, so at totality there's a ring of the Sun's disk still visible).

A third peculiarity of the Moon only became apparent when scientists got their first views of the far-Earth side around 1960, and they discovered that the far side had few maria -- the darker regions that were named for the Latin word for sea because it was thought early on that they might be water-filled oceans.  The largest two, the Oceanus Procellarum (Ocean of Storms) and the Mare Imbrium (Sea of Showers) together cover about 10% of the near-side disk of the Moon, and given that they're dotted with impact craters they seem to be very old structures.  (The first Apollo manned landing, in 1969 in the Mare Tranquillitatis (Sea of Tranquility), showed that the darkness of the maria is due to their being made largely of the dark volcanic rock basalt.)

[Image is licensed under the Creative Commons Gregory H. Revera, FullMoon2010, CC BY-SA 3.0]

So something odd is going on here, but a research team headed by geophysicist Stephen Elardo of the University of Florida has come up with a compelling answer to at least one piece of it.  The best hypothesis for the formation of the Moon, the researchers say, is the head-on collision of two protoplanets, one about ten times larger than the other (the smaller is estimated to be about the size of Mars).

Wouldn't that have been something to see?  From a safe distance?

In any case, this colossal collision blew both planets to smithereens, creating a whirling cloud of white-hot rocks and dust.  When the debris cooled and re-coalesced, the heavier one (eventually the Earth) had a high enough gravity to sort out the mess and pull the denser elements, like nickel and iron, into the core.  The lighter one (eventually the Moon) didn't, so it was left asymmetrical, with one side enriched in uranium, thorium, and the elements collectively called KREEP (potassium [symbol K], the Rare Earth Elements [such as cerium, lanthanum, dysprosium, and yttrium], and phosphorus [symbol P]).  This combo is what created the maria.  Uranium and thorium are radioactive, and as they decay, they release heat.  One effect of rocks being enriched in KREEP elements is that it lowers their melting point.  This meant that the surface remained liquid much longer -- becoming the flat, dark basalt plains we now can see from Earth.  The other side, being much lower in uranium, thorium, and KREEP, froze solid very early, and the landscape largely lacks maria.

"Because of the relative lack of erosion processes, the Moon's surface records geological events from the Solar System's early history," said study co-author Matthieu Laneuville, geophysicist at the Tokyo Institute of Technology, in an interview with ScienceDaily.   "In particular, regions on the Moon's near side have concentrations of radioactive elements like uranium and thorium unlike anywhere else on the Moon.  Understanding the origin of these local uranium and thorium enrichments can help explain the early stages of the Moon's formation and, as a consequence, conditions on the early Earth."

So that's one piece of the puzzle.  It brings up other questions, though, such as whether the fact that all this happened on the near-Earth side is a coincidence or was driven by something about the collision that formed the Earth-Moon system.  But whatever the answer to that is, the whole topic is fascinating -- and the violence of our satellite's origin is something to remember the next time you're looking up on a clear, peaceful moonlit night.

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This week's Skeptophilia book recommendation of the week is for anyone who likes quick, incisive takes on scientific topics: When Einstein Walked with Gödel: Excursions to the Edge of Thought by the talented science writer Jim Holt.

When Einstein Walked with Gödel is a series of essays that explores some of the deepest and most perplexing topics humanity has ever investigated -- the nature of time, the implications of relativity, string theory, and quantum mechanics, the perception of beauty in mathematics, and the ultimate fate of the universe.  Holt's lucid style brings these difficult ideas to the layperson without blunting their scientific rigor, and you'll come away with a perspective on the bizarre and mind-boggling farthest reaches of science.  Along the way you'll meet some of the key players in this ongoing effort -- the brilliant, eccentric, and fascinating scientists themselves.

It's a wonderful read, and anyone who is an aficionado of the sciences shouldn't miss it.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]