Sphere itself

A loyal reader of Skeptophilia asked me what I knew about a strange geological oddity called "Klerksdorp spheres," which are round-ish objects with a metallic sheen, often with two or three parallel grooves at the equator, most commonly found near Ottosdal, South Africa.  They're a prominent feature in the arguments of the Ancient Astronauts crowd, where they're often claimed to have been dropped here on Earth during an alien visitation billions of years ago, only to be unearthed today.

His email said:

I'm not saying I agree with them -- in general I don't just accept far-fetched explanations -- but I've seen lots of photos of these things and they're peculiar.  It's hard for me to imagine how they could form naturally.  They're all over the place on webpages about "out of place artifacts," and a lot of people think they're evidence that we were visited by aliens in the distant past, or at least that early civilizations had a lot better technology than we thought was possible.  At least I thought I'd ask you what you think, and whether there's any chance these things aren't natural.

Well, first of all, thanks for asking.  To me, even if you lean toward weird or paranormal or non-scientific explanations, you can go a long way toward avoiding drowning in the Great Swamp of Woo simply by admitting that you don't know for sure.

The thing is, though, the paragraph from the email is basically the argument from incredulity -- "I can't imagine how this could happen" = "it must be aliens/magic/the supernatural/God."  (Intelligent design creationism is really nothing more than a religious version of the argument from incredulity.)  The proper response to "I can't imagine how this could happen" should be one of two things: (1) "... so I simply don't know the answer," or (2) "... so I'll try to find out more scientifically credible evidence about it."

As astrophysicist Neil deGrasse Tyson put it -- in this case, referring to UFOs -- "Remember what the 'U' in 'UFO' stands for.  It stands for 'unidentified.'  Well, if something is unidentified, it means you don't know what it is.  If you don't know what it is, that's where the conversation should end.  You don't then go on to say that 'therefore it must be' anything."

Anyhow, I chose option #2 and did a bit of looking into the question posed by the writer.  I won't argue that the Klerksdorp spheres are odd-looking:

[Image is in the Public Domain courtesy of photographer Robert Huggett]

If I found something like this, my first thought would certainly be to wonder if it was some sort of human-made artifact.  The thing is, they've been found in a three-billion-year-old pyrophyllite deposit in South Africa -- not somewhere you'd expect to find modern ball-bearings.

Here's the problem, though.  Rather than doing any kind of sober analysis, the Alien Manufacture cadre has perpetually misrepresented the actual facts about the spheres.  One of the worst is the "Vedic creationist" Michael Cremo, author of the book Forbidden Archaeology, who believes (amongst other things) that humans in more or less their present form have been around for millions, possibly billions, of years.  Here are a few of the verifiable facts that Cremo and others get wrong:

• The objects are "perfect spheres."  Anyone with intact vision can see from the example shown that they're relatively symmetrical oblate spheroids, but are far from perfect spheres.
• They're made of a nickel-steel alloy "only known from human manufacture."  In fact, detailed analysis found them to be composed of a combination of hematite (Fe2O3) and wollastonite (CaSiO3).
• The objects, once placed on a shelf in a "vibration-free case" in a museum in Klerksdorp, "rotated by themselves."  This seems to have been a misquotation of the museum curator, Roelf Marx, who stated that the spheres had been jostled by tremors caused by underground blasting in gold mines, and that maybe the cases weren't as vibration-free as they needed to be.
• They're "far harder than tempered steel."  In fact, the ones tested are around 5.0 on the Mohs scale of hardness.  For reference, that's a bit softer than window glass.
• They even get the nature of the mine wrong; the Wonderstone Mine, where most of the Klerksdorp spheres were found, has been repeatedly called a "silver mine" even though silver has never been mined there.  It's a pyrophyllite mine -- a silicate mineral with a multitude of industrial uses, including as an additive to clay in brick-making.

I've nothing against speculating; sometimes shrewd guesses lead to productive lines of scientific inquiry.  But fer cryin' in the sink, at least don't lie about the facts.  Nothing is gained by misrepresenting the actual verifiable data, except possibly to destroy every vestige of credibility you had.

In fact, the Klerksdorp spheres -- odd-looking though they admittedly are -- are almost certainly concretions, sedimentary rocks that start out with a grain of something (probably in this case wollastonite), and then have repeated deposits of additional minerals, creating concentric layers in exactly the same way pearls form in oysters.  (In fact, Klerksdorp spheres that have been cut in half show the internal onion-like layers you'd expect in a concretion.)  The grooves seem to be the external manifestation of lamina, parallel internal sheets that are indicative of the objects' orientation when they formed.

In other words: they're entirely natural.  They're not alien ball bearings or artifacts from a three-billion-year-old human civilization.  They are not "out-of-place artifacts;" they are, in fact, found exactly where they should be.

So to the original reader who emailed me; honestly, thanks for asking, and keep asking questions like that.  There's nothing wrong with being puzzled, and even (for a time) wondering if something strange is going on.  As long as you don't stop there, you're on the right path.  The argument from incredulity isn't a problem until it becomes a solid wall.

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Taken by the flood

It amazes me the mental gymnastics the biblical fundamentalists will go through to use scientific studies to shore up their contention that the Bible is literally, word-for-word true.

We've seen this sort of pretzel logic here before, of course.  Eleven years ago I did a piece about a cool scientific discovery that a mineral called ringwoodite, which contains about one percent (by mass) chemically-bound water, was abundant in the Earth's mantle, which prompted the biblical literalists to jump up and down yelling, "See?  We told you.  That's where all the water went after the Great Flood!  Ha!  Q.E.D."  A few also pointed out that in Genesis 7:11 we read that God "broke up the fountains of the deep," so this could also have been the source of some of the flood waters as well.

Never mind that the ringwoodite is six hundred or more kilometers beneath the Earth's surface, and if God "broke up the fountains" to that extent, what would come out would not be water but superheated magma.

So more flood basalt than conventional flood, really.  Not something you'd want to float your Ark on, especially if it was made of wood.

It was with only mild surprise that I saw similar reactions to a study that came out this week from the King Abdullah University of Science and Technology.  You might recall that earlier this week I alluded to the Zanclean Flood -- the astonishing event that occurred about 5.3 million years ago, where plate movement temporarily closed off the Straits of Gibraltar, resulting in the Mediterranean Sea drying up almost completely.  This was followed by a sudden re-opening of the gap and the creation of the Mother of All Waterfalls over the Gibraltar Sill, at its peak refilling the Mediterranean at a rate of an astonishing ten meters a day.

What I didn't know was that apparently a similar thing happened to the Red Sea.  It shouldn't have been a surprise, really; the Red Sea is like the Mediterranean in having only a single narrow connection to the world's oceans (the Straits of Bab-el-Mandeb), if you don't count the Suez Canal.  It's also a tectonically-active region, with the Red Sea Rift underlying the entire thing lengthwise, terminating at its south end in the geologically complex Afar Triple Junction.

[Image licensed under the Creative Commons Eric Gaba (Sting - fr:Sting), Red Sea topographic map-en, CC BY-SA 4.0]

Well, the research found geological evidence of a similar scenario to the Zanclean Flood; a tectonic shift closing off the strait, followed by evaporation of nearly all of the water, followed by a second shift reopening the strait and refilling the sea.  "Our findings show that the Red Sea basin records one of the most extreme environmental events on Earth, when it dried out completely and was then suddenly reflooded," said study lead author Tihana Pensa.  "The flood transformed the basin, restored marine conditions, and established the Red Sea's lasting connection to the Indian Ocean."

I'm guessing y'all can see where this is going.

The fundamentalists are twisting themselves into knots saying, "See?  We told you.  Moses parting the Red Sea, Pharaoh's army, the waters rushing back!  Ha!  Q.E.D."

Well, needless to say -- or, more accurately, I wish it was needless to say -- there are a few holes in this claim.

First, the study at KAUST explicitly says that the transformation from salty desert back to a water-filled Red Sea was far slower than the Zanclean Flood, and is estimated to have taken a hundred thousand years.  So Pharaoh's army must have been really slow on the uptake.  If they couldn't get out of the way of a flood creeping along at that rate, they deserved everything they got.

Second, the biblical apologists also conveniently leave out that the study found the Red Sea flood happened 6.2 million years ago -- so almost a million years before the much bigger Zanclean Flood.  At this point, there were no modern humans around, and wouldn't be for about another five million years.  Our likely ancestor who would have been alive back then was Orrorin tugenensis, who has been reconstructed to look something like this:

I don't know about you, but when I picture the characters from the Old Testament, this isn't the image that comes to mind.  Although I have to say, it would have made the movie The Ten Commandments a lot more entertaining:

Moses:  Fear not!  The Lord of Hosts will do battle for us!

Israelites:  *excited hooting, one of them throws a femur into the air*

However, the people who can already twist their logical faculties around enough to believe that the Bible is the literal truth will also happily conclude that (1) the KAUST team got the chronology wrong by a factor of 1,000, and (2) the Red Sea could have filled a lot faster than that, because God.

Oh, and (3) why are there still monkeys?

You can not win with these people.  Funny the confidence you can get from assuming your conclusion.

Anyhow.  My general opinion is if you want to believe the Bible is the infallible Word of God, knock yourself out.  As long as you don't try to get it taught as science in public schools, you can believe the universe was created by a Giant Green Bunny from the Andromeda Galaxy, as far as I care.  But a word of advice -- when you start cherry-picking convenient bits of science to support Fundamentalist Bunnyology, and avoiding the much more numerous bits that contradict it, I reserve the right to make fun of you.

Not that I expect it to have any effect.  The creationists, I've found, are as impervious as Noah's lava-proof Ark.

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Birdwalking into the Miocene

From the One Thing Leads To Another department, we have: a cute little fuzzy mammal from Madagascar, some thoughts about genetic drift, and a period of geological history during which a lot was happening.

I'd like to say that this kind of twisty mental path is infrequent for me, but unfortunately, it happens pretty much on a daily basis, and has since I was a kid.  When I was around twelve years old, my parents splurged on a set of Encyclopedia Brittanica, ostensibly to assist me with my schoolwork, but they (the Encyclopedia, not my parents) were honestly more of a hindrance than a help.  I'd go to the Brittanica to look up, say, something about the Monroe Doctrine for social studies class, and my mom would find me three hours later with fifteen open volumes spread on the floor around me, with me in the middle immersed in an article about venomous snakes in Malaysia.

It's why conversations with my older son, with whom I seem to share a brain, are like some kind of weird exercise in free association.  We've occasionally tried to reconstruct the pathway by which we got to a particular topic, and there's usually a logical connection between each step and the preceding one, but overall, our discussions give new meaning to the word labyrinthine.

Anyhow, today I started on this particular birdwalk when someone posted a photograph on social media of an animal I'd never heard of: the ring-tailed vontsira (Galidia elegans).  The vontsira is kind of adorable:

[Image licensed under the Creative Commons Charles J. Sharp creator QS:P170,Q54800218, Ring-tailed vontsira (Galidia elegans) 2, CC BY-SA 4.0]

The vontsira and its relative the falanouc are in the family Eupleridae along with a species I had heard of, the fossa, which is a sleek, elegant, weasel-like animal that is only distantly related to other members of the Order Carnivora.  All of the eupleurids live in Madagascar, and like most of the endemic species on the island, they're threatened by habitat loss and competition from non-native species.

What I found most curious about these mammals is that they're a clade -- genetic studies have found that eupleurids all descend from a single small population that arrived in Madagascar something like twenty million years ago, and then diversified into the species you see today.  Chances are, the ancestors of the vontsira, falanouc, fossa, and other eupleurids came over from Africa via rafting in the early Miocene Epoch.  They're distant cousins of the much more common and widespread mongooses, hyaenas, genets, and civets, and it was probably some prehistoric viverroid (the parvorder that includes all five groups) that made its way to Madagascar and gave rise to modern eupleurids.

This led me to looking into what was happening, geology-wise, during the Miocene.  I knew it was a busy time, but I didn't realize just how busy.  Tectonic movement closed off the Mediterranean Sea from the Indian Ocean, and then a shift at the western end of the Mediterranean closed off the Straits of Gibraltar; the result was that the Mediterranean dried up almost completely, something called the Messinian salinity crisis because what was left was a salty desert with an average temperature of something like 110 F and two disconnected lakes of concentrated brine.  At the end of the epoch, another plate movement reopened the Straits, and there was a flood of a magnitude that beggars belief; at its peak, the flow rate was enough to raise the level of the refilling Mediterranean by ten meters per day.

This is also the period during which the Indian subcontinent rammed into Asia, raising the Himalayas and introducing a bunch of African species into Asia (this is why there are lemurs in Madagascar and India, but none in the Middle East).  Also, it's when the Columbia River Flood Basalts formed -- an enormous (175,00 cubic kilometers) blob of igneous rock covering what is now eastern Washington and Oregon, and the west parts of Idaho -- an eruption probably due to the same hotspot which now underlies Yellowstone.

Because of all this, the climate during the Miocene might as well have been attached to a yo-yo.  Warm periods rapidly alternated with cold ones, and wet with dry.  As you might imagine, this played hell with species' ability to adapt, and groups came and went as the epoch passed -- the borophagine ("bone-crushing") canids, the terrifying "hypercarnivorous" hyaenodonts, and the enormous, superficially pig-like entelodonts amongst them.  The first apes evolved, and the split between the ancestors of modern humans and modern chimps occurred in the late Miocene, something like seven million years ago.

If all that wasn't enough, some time during the Miocene -- geologists are uncertain exactly when -- there was an asteroid impact in what is now Tajikistan, forming the twenty-five-kilometer-wide Karakul Crater Lake, which at an elevation of 3,960 meters is higher than the much better-known Lake Titicaca.

So there you have it.  A brief tour of the chaotic paths through my brain, starting with a furry woodland animal from Madagascar and ending with a meteorite impact in Tajikistan.  Hopefully you found some stops along the way interesting.  Now y'all'll have to excuse me, because I need to go look up a single fact in Wikipedia to answer a question a friend asked about linguistics.  You'll find me in a few hours reading about how general relativity applies to supermassive black holes.

I'm sure how I got there will make sense to me, at least.

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Anomaly analysis

I try to be tolerant of people's foibles, but one thing that annoys the absolute hell out of me is when someone is obviously ignorant of the basic facts of a subject, and yet expects everyone to treat their opinion about it as if it had merit.

It's why "the Big Bang means nothing exploded and made everything" (cosmology) and "why are there still monkeys?" (evolutionary biology) both make me see red almost instantaneously.  Fer cryin' in the sink, if you're going to talk about something, at least take the five minutes it requires to read the fucking Wikipedia page on the topic first.  Yes, I suppose you're "entitled to your opinion" regardless, but I'm in no way required to treat such idiocy as if it were Stephen Hawking levels of brilliance.

I mean, I have a lot of faults, but one thing I try to avoid is pontificating on subjects about which I am ignorant.  I have a pretty good idea of the limits of my own knowledge, and I am unhesitating in saying, "Sorry, I don't know enough to comment about that."

It's really not that hard to say.  Try it, you'll see.

What brings this whole infuriating subject up is all the people who weighed in on something that is honestly a very cool piece of research, which came out in the journal Geophysical Research Letters last week.  A team led by geophysicist Charlotte Gaugné-Gouranton, of Paris City University, used satellite data to analyze a peculiar shift in the Earth's gravitational field that affected a huge region of the eastern Atlantic Ocean.

The team is uncertain what caused the anomaly, which lasted for about two years and then subsided back into its original state.  "By analyzing time series of GRACE [Gravity Recovery and Climate Experiment]-derived gravity gradients, we have identified an anomalous large-scale gravity gradient signal in the eastern Atlantic Ocean, maximum at the beginning of 2007, which cannot be fully explained by surface water sources nor core fluid flows," the researchers wrote.  "This leads us to suggest that at least part of this signal could reflect rapid mass redistributions deep in the mantle."

The team suspects it might have been caused by a sudden phase transition in a common mantle mineral called bridgmanite (Mg,Fe(SiO3)), which could cause mass redistribution because of changes in density, similar to what happens when water freezes into ice.  But further research is needed to confirm this explanation.

Well, in a classic case of people adding 1 + 1 and getting 73.8, we immediately had dozens of self-styled experts adding "anomaly" to "gravity" and multiplying by "cannot be fully explained" and getting... well, take a look for yourself:

• "Advanced technology of alien manufacture is capable of 'shielding' from gravity and is the means of FTL propulsion that's been observed over and over.  This 'blink' means it's finally been captured by scientific equipment.  Countdown until the government denials start."
• "Disruptions like this are to be expected during the End Times.  Hell is on the move."
• "The scientists know more than they're letting on.  I wouldn't live along the East Coast of the United States if you paid me.  Connections to La Palma?"  [Nota bene: La Palma is one of the Canary Islands, home to a volcano that has been erupting intermittently since 2021, and was the subject of a rather hysterical BBC documentary in 2000 about how the island could split in half and cause a megatsunami -- something geologists have determined is extremely unlikely]
• "When those windows open and close again, it is a sign of the Celestial Ascension.  We should expect more of the same very soon."
• "I'm surprised they let this study get published.  Something that can change the Universal Law of Gravity, and they're shrugging it off as an 'anomaly'?  But now that the secret is out, why hasn't this been headline news worldwide?"
• "The LHC [Large Hadron Collider] went online in 2008.  Not a coincidence.  It's only a theory, but they said that the LHC could create mini black holes, and this may be proof."
• "Movement within the Hollow Earth.  But movement of what?  Stay tuned, folks, this is big."

*brief pause to stop banging my head against my desk while whimpering softly*

Okay, let's all just hang on a moment.  First of all, this anomaly was vast in size, but tiny in magnitude.  The fluctuation was small enough that it was undetectable on the Earth's surface (the scientists' own words) and was only caught by highly sensitive sensors on satellites that had been specifically designed to detect minute shifts in the Earth's gravitational field.  Second, it wasn't a "blink" -- it lasted for over two years.  Third, it peaked back in 2007, so whatever it was ended seventeen years ago, and in that time we have seen no Atlantic megatsunamis, aliens, Celestial Ascensions, or hellmouths opening.  Fourth, a shift in the gravitational field just means "something with mass moved," not a "change in the Universal Law of Gravitation."  Fifth, if the LHC had created a dangerous mini black hole, you'd think the physicists right there in Switzerland would have been the first to know, not some geologists working out in the Atlantic.  Sixth, you can't give an idea legitimacy simply by adding the phrase "it's only a theory;" if a claim was stupid before, it's still stupid after you say that.  In fact, it might be even stupider.

Seventh, and most importantly: for fuck's sake, people.

Captain Picard has absolutely had it with this kind of nonsense.

It's not that we laypeople -- and I very much include myself in that term -- can't get carried away by the hype sometimes.  In fact, when I first read about the La Palma thing a few years ago, I was honestly kind of freaked out by it; devastating landslide-induced megatsunamis have happened before (in fact, long-term followers of Skeptophilia might recall that I've written about two of them here -- the Storegga Slide and the Agadir Canyon Avalanche).  But then I did what everyone should do when they're confronted with a claim outside of their area of expertise; I did a little digging to find out what the scientists themselves had to say on the topic, and I found out that just about all geologists agree that while La Palma is clearly seismically active, it's unlikely to fracture and create an ocean-wide megatsunami.

At that point, I just kind of went, "whew," and resumed business as usual.  I did not then go on to claim that the scientists were wrong, the island was too going to fracture, and aliens from the Hollow Earth were going to use their anti-gravity faster-than-light propulsion to come out and usher in either the End Times or the Celestial Ascension, depending on which version you went for earlier.

Look, it's not that there's anything specifically dangerous about thinking there's an alien base under the eastern Atlantic.  It's more that such fuzzy irrationality very quickly becomes a habit.  Once you're accustomed to demanding respect for a claim that upon examination turns out to be "this crazy, fact-free idea I just now pulled out of my ass," you begin to apply the same demand for your uninformed opinions on medicine, the economy, and politics.

Which in one sentence explains why the United States is currently a slow-motion train wreck.

It all goes back to what Isaac Asimov said in 1980, doesn't it?  Seems like a good place to end:

There is a cult of ignorance in the United States, and there has always been.  The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means "my ignorance is just as good as your knowledge."

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Celestial whack-a-mole

If a large meteorite collided with the Earth, it would seriously ruin your day.

Depending on its size and where it hit, it could ruin your next several decades.  Even a relatively small impactor -- such as the Chelyabinsk meteorite of 2013, that exploded over the southern Urals in Russia in 2013 -- did some significant damage, (fortunately) mostly to buildings.  It is estimated to have been about nine thousand tonnes and eighteen meters in diameter, and when it hit the atmosphere and detonated from thermal shock, it released about thirty times the energy of the nuclear bomb that destroyed Hiroshima.

And in the grand scheme of things, Chelyabinsk was nothing more than a pebble, of which there are likely to be millions out there in the Solar System, mostly (again, fortunately) not in orbits that threaten the Earth.  Bigger objects, such as the ten-kilometer Chicxulub meteorite that wrote finis to the Mesozoic Era, are fortunately far less common.

It's also a good thing that impacts have gotten less frequent over time.  The debris left over from the formation of the Solar System has gradually gotten swept up by the planets, either impacting them or being gravitationally flung out into space.  So comparatively speaking, we're safer now than we ever have been.  Four billion years ago, during the period called the Late Heavy Bombardment, there were so many impacts from asteroids and comets that the entire surface of the Earth re-liquified.  (One of the reasons that we have so few intact rocks left from the oldest periods of the planet's history.)

But just because in more recent geological history -- since, say, the beginning of the Cenozoic Era, 66 million years ago -- there have been fewer impacts, doesn't mean there have been none.  The reason the whole topic comes up is a study that came out this week in Nature Communications about the discovery of a three-kilometer wide crater, surrounded by concentric faults, caused by an meteorite impact 43 million years ago, that we hadn't even known about -- because it's underneath the North Sea.

Named the Silverpit Crater, it is thought to have been due to the collision of a 160-meter-diameter meteorite, traveling something like fifty kilometers per second.  The shock wave from the impact raised a tsunami estimated at a hundred meters high, that would have completely obliterated the coastlines of what is now England, Scandinavia, and the rest of northwestern Europe.

[Image credit: Uisdean Nicholson et al., Nature Communications, 20 September 2025]

While Silverpit didn't cause the global devastation that Chicxulub had, 23 million years earlier, it definitely would have caused problems, and not just for the region.  The impact would have blown tons of debris up into the atmosphere, dramatically lowering temperatures across the globe -- just as the eruption of Tambora did in 1815, causing the famous "Year Without a Summer."

If such an impact occurred today, it would have horrible consequences for the entire planet, likely including mass starvation because of widespread crop failure.

The question is what we could do to prevent such a catastrophe.  Even if we could detect an incoming meteor soon enough -- something iffier than ever, given Trump and his cronies' determination to completely sandbag NASA -- it's questionable that we'd have the lead time to try to deflect it into a safer path.  The DART Mission did exactly that, giving a nudge to the asteroid Dimorphos to change its orbit, so that was at least proof of concept -- but the DART lander itself took years to plan and build, and for something as small as the Silverpit impactor, it's unclear we'd know about it soon enough.

Other options -- like nuking the threatening meteor in space -- are dubious.  Even if you could blow up an asteroid, chances are all you'd accomplish is turn one incoming object into a hundred that were still on essentially the same trajectory.

So at present, I guess all we can do is hope for the best, and rely on the at least marginally-encouraging statistics that large meteor impacts are relatively uncommon.

Anyhow, that's our cheerful science news of the day.  The universe playing a game of celestial Whack-a-Mole with the Earth.  Me, I'm not going to worry about it.  On my list of Stuff I'm Experiencing Existential Dread About, this one ranks pretty low.  Certainly way behind climate change, various ongoing genocides, and the fact that my country's so-called leadership seems dead-set on turning the United States into Temu Nazi Germany.  Given all that, a meteorite collision might almost be an improvement.

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Mind the gap

In 1869, explorer John Wesley Powell did the first systematic study of the geology of the Grand Canyon.  As impressive as it is, the Grand Canyon's not that complicated geologically; it's made of layers of sedimentary rock, most of them relatively undeformed, one on top of the other from the oldest at the bottom to the newest at the top.  A layer cake of billions of years of Earth history, and a wonderful example of the principle of superposition -- that strata form from the bottom up.

However, Powell also noted something rather peculiar.  It's called the Great Unconformity.  In geologic parlance, an unconformity is a break in the rock record, where the layer below is separated from the layer above by a gap in time when either no rocks were deposited (in that location, at least), or the rocks that were laid down were later removed by some natural process.  At that stage in the science, Powell didn't know when exactly the Great Unconformity occurred, but it was obvious that it was huge.  Something had taken away almost a billion years' worth of rocks -- and, it was later found out, that same chunk of rock was missing not only at the future site of the Grand Canyon, but across most of North America.

It was an open question as to why this happened, but one leading hypothesis was that it was massive glaciation.  Glaciers are extraordinarily good at breaking up rocks and moving them around, as I find out every time I dig in my garden and my shovel runs into the remnants of the late Pleistocene continental glaciation.  At that point, where my house is would have been under about thirty meters of ice; the southern extent is the Elmira moraine, a line of low hills fifty kilometers south of here, left behind when the glaciers, pushing piles of crushed rock and soil ahead of them like a backhoe, began to melt back and left all that debris for us gardeners to contend with ten thousand years later.

There was a time in which the Earth was -- as far as we can tell -- completely covered by ice. The Cryogenian Period, during the late Precambrian, is sometimes nicknamed the "Snowball Earth" -- and the thawing might have been one contributing factor to the development of complex animal life, an event called the "Cambrian explosion," about which I've written before.

The problem was, the better the data got, the more implausible this sounded as the cause of the Great Unconformity.  The rocks missing in the Great Unconformity seem to have preceded the beginning of the Cryogenian Period by a good three hundred million years.  And while there were probably earlier periods of worldwide glaciation -- perhaps several of them -- the fact that the Cryogenian came and went and didn't leave a second unconformity above the first led scientists away from this as an explanation.

However, a paper in Proceedings of the National Academy of Sciences, written by a team led by Francis Macdonald of the University of Colorado - Boulder, has come up with evidence supporting a different explanation.  Using samples of rock from Pike's Peak in Colorado, Macdonald's team used a clever technique called thermochronology to estimate how much rock had been removed.  Thermochronology uses the fact that some radioactive elements release helium-4 as a breakdown product, and helium (being a gas) diffuses out of the rock -- and the warmer it is, the faster it leaves.  So the amount of helium retained in the rock gives you a good idea of the temperature it experienced -- and thus, how deeply buried it was, as the temperature goes up the deeper down you dig.

What this told Macdonald's team is that the Pike's Peak granite, from right below the Great Unconformity, had once been buried under several kilometers of rock that then had been eroded away.  And from the timing of the removal -- on the order of a billion years ago -- it seems like what was responsible wasn't glaciation, but the formation of a supercontinent.

But not Pangaea, which is what most people think of when they hear "supercontinent."  Pangaea formed much later, something like 330 million years ago, and is probably one of the factors that contributed to the massive Permian-Triassic extinction.  This was two supercontinents earlier, specifically one called Rodinia.  What Macdonald's team proposes is that when Rodinia formed from prior separate plates colliding, this caused a huge amount of uplift, not only of the rocks of the continental chunks, but of the seafloor between them.  A similar process is what formed the Himalayas, as the Indian Plate collided with the Eurasian Plate -- and is why you can find marine fossils at the top of Mount Everest.

[Image is in the Public Domain]

When uplift occurs, erosion increases, as water and wind take those uplifted bits, grind them down, and attempt to return them to sea level.  And massive scale uplift results in a lot of rock being eroded.

Thus the missing layers in the Great Unconformity.

"These rocks have been buried and eroded multiple times through their history," study lead author Macdonald said, in an interview with Science Daily.  "These unconformities are forming again and again through tectonic processes.  What's really new is we can now access this much older history...  The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents.  There are differences, and now we have the ability to perhaps resolve those differences and pull that record out."

What I find most amazing about this is how the subtle chemistry of rock layers can give us a lens into the conditions on the Earth a billion years ago.  Our capacity for discovery has expanded our view of the universe in ways that would have been unimaginable only thirty years ago.

And now, we have a theory that accounts for one of the great geological mysteries -- what happened to kilometer-thick layers of rock missing from sedimentary strata all over North America.

John Wesley Powell, I think, would have been thrilled.

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Old as the hills

In northwestern Australia, there's an administrative region called Pilbara.

Even though on a map, it looks kind of long and narrow, it's big.  The area of Pilbara is just shy of that of California and Nevada put together.  (I suspect that I'm like many non-Australians in consistently forgetting just how big Australia is.  It's the sixth largest country in the world, and is almost the same size as the continental United States.  Flying from Sydney to Perth is comparable to flying from Atlanta to Los Angeles.)

Pilbara is also extremely hot and dry, and very sparsely populated, with only a bit over sixty thousand residents total, most of whom live in the western third of the region.  The northeastern quadrant is part of the aptly-named Great Sandy Desert, one of the most inhospitable places on Earth.  There are only a few Indigenous tribes that somehow eke out a living there, most notably the Martu, but by and large it's uninhabited.

[Image licensed under the Creative Commons Brian Voon Yee Yap, aka Yewenyi, at en.wikipedia]

What brings up the topic, though, is that Pilbara is interesting for another reason than its hostile climate.

It is the home to some of the oldest rocks on Earth.

The Pilbara Craton -- a craton is a contiguous piece of continental crust -- is estimated to be around three and a half billion years old.  For reference, the Earth's crust only solidified 4.4 billion years ago.  Since that time, plate tectonics took over, and as I've described before, tectonic processes excel at recycling crust.  At collisional margins such as trenches and convergent zones, usually one piece slides under the other and is melted as it sinks.  Even in places where two thick, cold continental plates run into each other -- examples are the Alps and the Himalayas -- the rocks are deformed, buried, or eroded.

The result is we have very few really old rocks left.  The only ones even on the same time scale as Pilbara are the Barberton Greenstone Belt of South Africa and the Canadian Shield (and even the latter has been heavily metamorphosed since its formation).

This makes Pilbara a great place to research if you're interested in the conditions of the Precambrian Earth -- as long as you can tolerate lots of sand, temperatures that often exceed 36 C, and a fun kind of grass called Triodia that has leaf margins made of silica.

Better known as glass.

Frolicking in a field of Triodia is like running through a meadow made of Exacto knives.

Be that as it may, geologists and paleontologists have begun a thorough study of this fascinating if forbidding chunk of rock.  The most recent reconstructions suggest that both Pilbara and the aforementioned Barberton Greenstone were once part of an equatorial supercontinent called Vaalbara (which preceded the supercontinent most people think of -- Pangaea -- by a good three billion years).  And those might be the only chunks of that enormous piece of land left intact.

There are two other reasons Pilbara is remarkable.

It contains numerous fossilized stromatolites, which are layered sedimentary structures formed by cyanobacteria, thought to be the earliest photosynthetic life forms.  There are still stromatolites forming today -- probably not coincidentally, in shallow bays in Western Australia.

[Image licensed under the Creative Commons photographer Paul Harrison (Reading UK), March 2005, Stromatolites growing in Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia.]

As such, the Pilbara stromatolite fossils are the oldest certain traces of life on Earth, dating to 3.48 billion years ago.

The other reason is that it's also home to a massive impact crater dating to 3.47 billion years ago.  Shortly after those earliest, tentative life forms were living and thriving in the warm shallow ocean waters, a huge meteorite struck near what is now the town of Marble Bar, forming a crater and shatter cone between 16 and 45 kilometers in diameter (because of erosion, it's hard even for the geologists to determine where its edges lie).  The resulting Miralga Impact Structure blew tremendous amounts of molten debris up into the air, and some of it landed on that chunk of Vaalbara that would eventually end up in South Africa -- only to be recovered by geologists almost three and a half billion years later.

So there's a place in Australia that gives new meaning to the phrase "old as the hills."  Given its remoteness and inhospitable climate, I'm unlikely ever to visit there, but there's something appealing about the idea.  Walking on rock that is an intact remnant of a continent from over three billion years ago is kind of awe-inspiring.  Even if all the other rock is still here somewhere -- melted and reformed and eroded multiple times -- the idea that this chunk of the Earth has somehow lasted that long more or less intact is mighty impressive.

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News from Afar

I've written here before about the fact that the continents are in motion, something that is only not staggering because we've all known about it since ninth grade Earth Science class.  You can easily see why it took so long to accept.  First, the motion is so slow that it was, for most of human history, beyond the limitations of the technology available at the time to measure directly.  Second, it's just hard to imagine.

Continents?  Moving in solid rock?  What?

But move they do, and it's because if you go down far enough, the rock isn't solid.  Get into the upper mantle, and it's the consistency of taffy, so it flows, pushed by subterranean convection currents.  Those currents create drag forces on the undersides of the tectonic plates, shifting them around.  Although this is an oversimplification, in general, there are three ways that plates can move relative to each other:

• Convergent zones, where plates come together.  When thin, brittle oceanic plates are pushed toward each other, one usually bends and slides under the other at a thrust fault or subduction zone; the subducted plate and the sediment riding on it eventually melt, and the hot, water-rich magma rises to form chains of volcanoes parallel to the fault.  Examples are the Japan Trench and the Sumatra Trench.  When an oceanic plate collides with a thick, cold continental plate, you still get volcanoes boring their way up through the continent -- this is the origin of the Cascade Range.  If it's two continental plates colliding, the rock simply crumples up to form mountains -- such as what is happening in the Alps and Himalayas,
• Divergent zones, where plates move apart.  This is what's happening along the Mid-Atlantic Ridge, and is why the island of Iceland is volcanic -- the eastern and western halves of the island are moving apart, and new basaltic lave bubbling up to fill the gap.

A photograph I took at Meradalir Volcano in Iceland, August 2022

• Strike-slip faults, or transform faults, which occur when plates slide in opposite directions parallel to the fault.  Examples are the San Andreas, Hayward, and Elsinore Faults in California, and the Alpine Fault in New Zealand.

All of these movements can significantly transform the shapes and positions of the continents -- you probably know that 250 million years ago, most of the Earth's land masses were assembled into a giant supercontinent (Pangaea), and the seas into a massive superocean (Panthalassa), with huge consequences to the climate.  Fascinating to realize, though, that Pangaea was only the most recent of the supercontinents; geologists believe that the same lumping-it-all-together occurred at least three or four times before then.

And the reverse can happen, too, when a divergent zone forms underneath a continent, and it tears the land mass in two.  In fact, this is the reason the topic comes up today; a paper last week in Nature Geoscience about the Afar Triple Junction, the point where three faults meet at one point (the Red Sea Rift, the Aden Ridge, and the East African Rift).  Geologists have found that underneath this region, there's a mantle plume -- an upwelling of very hot magma -- that is pulsing like a giant beating heart, driving convection that will eventually tear Africa in two, shearing off a chunk from Ethiopia to Mozambique and driving it east into the Indian Ocean.

[Image licensed under the Creative Commons Val Rime, Tectonic African-Arabian Rift System, CC BY-SA 4.0]

"We have found that the evolution of deep mantle upwellings is intimately tied to the motion of the plates above," said Derek Keir, of the University of Southampton, who co-authored the study.  "This has profound implications for how we interpret surface volcanism, earthquake activity, and the process of continental breakup...  The work shows that deep mantle upwellings can flow beneath the base of tectonic plates and help to focus volcanic activity to where the tectonic plate is thinnest.  Follow on research includes understanding how and at what rate mantle flow occurs beneath plates."

The formation of a new sea -- and the consequent turning of much of east Africa into an island -- isn't exactly what I'd call "imminent;" it's predicted that the Red Sea will breach the Afar Highlands and flood the lowest points of the rift (much of which is already below sea level) in something like five million years.  The region will be highly tectonically active throughout the process, however, and there'll be enough volcanoes and earthquakes in the meantime to keep us interested.

It's a good reminder that although mountains and oceans have been a symbol of something eternal and unchanging, in reality everything is in flux.  It recalls to mind the lines from Percy Shelley's evocative poem "Mont Blanc," which seems a fitting way to end:

Yet not a city, but a flood of ruin
Is there, that from the boundaries of the sky
Rolls its perpetual stream; vast pines are strewing
Its destin’d path, or in the mangled soil
Branchless and shatter’d stand; the rocks, drawn down
From yon remotest waste, have overthrown
The limits of the dead and living world,
Never to be reclaim’d.  The dwelling-place
Of insects, beasts, and birds, becomes its spoil;
Their food and their retreat for ever gone,
So much of life and joy is lost.  The race
Of man flies far in dread; his work and dwelling
Vanish, like smoke before the tempest’s stream,
And their place is not known.  Below, vast caves
Shine in the rushing torrents’ restless gleam,
Which from those secret chasms in tumult welling
Meet in the vale, and one majestic River,
The breath and blood of distant lands, for ever
Rolls its loud waters to the ocean-waves,
Breathes its swift vapours to the circling air.

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A perilous beauty

Ever heard of the "Bonneville Slide?"

It sounds like some obscure country line dance, but the real story is more interesting, and it comes with a connection to a curious Native legend that turns out to refer to a real historical event.

The Klickitat People have lived for centuries on both sides of the Columbia River, up into what is now Skamania and Klickitat Counties, Washington, and down into Multnomah and Clackamas Counties, Oregon.  They tell the tale of Pahto and Wy'east, the two sons of the chief of all the gods, Tyhee Saghalie.  The two young men did not get along, and fought over who would rule over which parcel of land.  Their father shot one arrow south and the other north; Pahto was given the lands around where the northern arrow landed, and Wy'east the territory surrounding where the southern arrow fell to the ground.  Tyhee Saghalie then shook the Earth and created a great bridge across the Columbia River so the two could visit each other.

But soon trouble broke out again.  Pahto and Wy'east both fell in love with the same young woman, the beautiful Loowit, and began to fight, burning villages and destroying forests and crops.  Tyhee Saghalie tried to reason with them, but to no avail.  In the end he grew angry himself and shook the Earth again, destroying the bridge; the cataclysm created a flood that washed away whole forests.  He turned all three into mountains -- Wy'east became Mount Hood, Pahto Mount Adams, and the lovely Loowit Mount Saint Helens.  But even in mountain form they never forgot either their anger or their burning love, and all three still rumble and fume to this day.

What is fascinating is that this odd story actually appears to have some basis in fact.

In around 1450 C.E., an earthquake knocked loose about a cubic kilometer of rock, soil, and debris from Table Mountain and Greenleaf Peak.  The resulting landslide -- the Bonneville Slide  -- roared down the Columbia Gorge, creating a dam and what amounted to a natural bridge something like sixty meters high across one of the biggest rivers in the world.  

Greenleaf Peak today [Image licensed under the Creative Commons Eric Prado, Greenleaf Peak, Washington, CC BY-SA 4.0]

The dam couldn't last, however.  The Columbia River has a huge watershed, and the lake that built up behind the dam eventually overtopped the natural "Bridge of the Gods."  The whole thing collapsed -- probably during a second earthquake -- releasing all that pent-up river water in a giant flood.  It left behind geological evidence, both in the form of a layer of flood-damaged strata west of the slide, and the remains of drowned forests to the east, where trees had died as the dammed lake rose to fill the gorge.

Despite the reminder we got in 1980 -- with the eruption of Mount Saint Helens -- it's easy to forget how geologically active the Pacific Northwest is.  Not only is there the terrifying Cascadia Subduction Zone just offshore (about which I wrote two years ago), the other Cascade volcanoes, from Silverthrone Caldera (British Columbia) in the north to Lassen Peak (California) in the south, are still very much active.  Right in the middle is the massive Mount Rainier, visible from Seattle, Tacoma, and Olympia on clear days, which is one of the most potentially destructive volcanoes in the world.  Not only is it capable of producing lava and pyroclastic flows, it's capped by huge glaciers that would melt during an eruption and generate the catastrophic mudflows called lahars.  The remnants of two historical flows from Rainier -- the Osceola and Electron Lahars -- underlie the towns of Kent, Orting, Enumclaw, Puyallup, Auburn, Buckley, and Sumner, and in some places are twenty to thirty meters deep.

The Earth can be a scary, violent place, but somehow, humans manage to survive even catastrophic natural disasters.  And, in the case of the Bridge of the Gods, to incorporate them into our stories and legends.  Our determination to live in geologically-active areas is due to two things; volcanic soils tend to be highly fertile, and we have short memories.  Fortunately, though, we couple what seems like a foolhardy willingness to take risks with a deep resilience -- allowing us to live in places like the Cascades, which are bountiful, and filled with a perilous beauty.

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