Deep impact

It's remarkably hard to find evidence of impact craters on the Earth.

If you're thinking, "What's the difficulty?  Just look for a big hole in the ground," you're probably thinking of one of two things -- either craters on the Moon, or Barringer Crater near Winslow, Arizona.  The craters on the Moon stick around pretty much indefinitely because the airless, waterless surface experiences virtually no erosion; as far as Barringer, the impact that caused it only happened around fifty thousand years ago, which is the blink of an eye, geologically speaking.  (Plus, it's in the high desert, with little vegetation to hide underneath.)

With older impact craters, the forces of erosion eat away at the telltale signs -- the raised, oval or circular ridges, especially.  The oldest craters have been destroyed by subsequent tectonic shifts and faults, and (for ones in oceanic plates) because the damaged strata themselves were subducted and melted.

One massive impact crater that was only detected in 1983 -- despite the fact that tens of thousands of people live more or less right on top of it -- is the one left by the Chesapeake Bay Impact Event, which occurred during the Eocene Epoch, on the order of 35.5 million years ago.  At that point, the impact site, on the southern tip of the Delmarva Peninsula, was coastal tropical rainforest; the global temperature was still dropping following the massive Paleocene-Eocene Thermal Maximum, but was still a good two degrees Celsius warmer than today.  The mass of the impactor isn't known for certain -- it was completely vaporized -- but it's estimated to have been about three kilometers across and traveling at eighteen kilometers per second, and punched a hole eight kilometers deep into the crystalline basement rock, blasting the sediments on top to smithereens and creating a crater over eighty kilometers across.  Because at least part of the impact was in the shallow ocean, it also created a massive tsunami that travelled inland as far as the foothills of the Blue Ridge Mountains.

Since the impact, it refilled -- first with unconsolidated, unsorted sediments, essentially broken up pieces of the rock that was blown out from the collision, then with eroded material as the whole place gradually settled down.  Part of it was refilled with seawater.  The only way it was discovered was the presence of an anomalous "fault" that turned out to be the edge of the crater wall, followed by the analysis of some rock cores that showed a huge, thick layer of jumbled junk that geologists figured out was the debris formed as the crater walls slumped inward.  It also explained the North American Tektite Field, an enormous splatter field of what amounts to cooled droplets of melted rock.

But visiting the area today, you don't see much that would tell you that only thirty-five million years ago, the place got slammed by an enormous chunk of rock from outer space.

[Image is in the Public Domain courtesy of the United States Geological Survey]

Even the much larger Chicxulub Impact Crater, near the Yucatán Peninsula, took a lot of work to identify.  It's just shy of twice as old as the Chesapeake Bay site (about 66 million years), and is almost entirely underwater and filled with oceanic sediments.  Today, the impact site that ended the 180-million-year hegemony of the dinosaurs is only visible to sensitive gravitometers and magnetometers.

Which makes the discovery of an impact crater 3.47 billion years old, in East Pilbarra, Western Australia, even more astonishing.

A paper in Nature Communications this week, authored by Christopher Kirkland of Curtin University et al., shows convincing evidence of an impact crater over a hundred kilometers wide near the northwestern coast of Australia.  The center of the crater shows regions of shocked crystalline rock, along with layers of breccia (the same sort of jumble of debris found at the Chesapeake Bay site).  Further stratigraphic work has confirmed that this was, indeed, the site of a "massive hypervelocity impact."  This makes it the only Archaean-age crater known to have survived.

The authors write:

Despite the high modeled frequency of bolide impacts in the early Archaean, the rarity of verified impact craters of Archaean age suggests that: (a) the impact flux was much less than predicted by lunar data; (b) the evidence has been eradicated, or (c) that we have failed to recognise them.  On a young Earth covered in primitive (mafic–ultramafic) crust, identifying shatter cones or impact breccias may represent the best chance of finding other large Archaean impact structures.  However, these highly fractured rocks will be the first to undergo (presumably intense) weathering and erosion.  Notwithstanding their fragility, we believe many more Archaean craters await discovery.

Myself, I think it's astonishing that they've found even one.  For any traces to have survived for nearly three and a half billion years is staggering.  At that point, life was only getting started; the first known microbes appeared 3.7 billion years ago, and when the impact occurred, it would still be another half a billion years before the first certain multicellular life.  So unlike the Chesapeake Bay and Chicxulub Impacts, which were (respectively) regionally and globally devastating to life, the East Pilbarra collision probably didn't make much of... um... an impact.

But it definitely stirred things up, created an enormous crater and rain of debris, and would have been a dramatic thing to witness.  From a safe distance.  The fact that even today, 3.47 billion years later, geologists can detect the hole it left behind, indicates that it was one hell of a punch.

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Hands, skulls, and colours

In H. P. Lovecraft's terrifying and atmospheric 1927 short story "The Colour Out of Space," a meteorite strikes near a farmhouse in a rural area "west of Arkham," the fictional town in Massachusetts that is the setting of many of his stories.

The farm's owner, Nahum Gardner, and many others witness its fall; a "white noontide cloud... [a] string of explosions in the air, and [a] pillar of smoke from the valley."  Nahum, being closest, goes to investigate:

By night all Arkham had heard of the great rock that fell out of the sky and bedded itself in the ground beside the well at the Nahum Gardner place...  Nahum had come to town to tell people about the stone...  He and his wife went with three professors from Miskatonic University who hastened out the next morning to see the weird visitor from unknown stellar space, and wondered why Nahum had called it so large the day before.  It had shrunk, Nahum said as he pointed out the big brownish mound above the ripped earth and charred grass near the archaic well-sweep in his front yard; but the wise men answered that stones do not shrink.  Its heat lingered persistently, and Nahum declared it had glowed faintly in the night.  The professors tried it with a geologist's hammer and found it was oddly soft.  It was, in truth, so soft as to be almost plastic; and they gouged rather than chipped a specimen to take back to the college for testing.  They took it in an old pail borrowed from Nahum's kitchen, for even the small piece refused to grow cool...

The day after that... the professors had trooped out again in great excitement...  [T]he specimen... had faded wholly away when they put it in a glass beaker.  The beaker had gone as well, and the men talked about the strange stone's affinity for silicon.  It had acted quite unbelievably in that well-ordered laboratory; doing nothing at all and showing no occluded gases when heated on charcoal... and soon proving itself absolutely non-volatile at any producible temperature, including that of the oxy-hydrogen blowpipe.  On an anvil it appeared highly malleable, and in the dark its luminosity was very marked.  Stubbornly refusing to grow cool... upon heating before the spectroscope it displayed shining bands unlike any known colours of the normal spectrum.

Eventually, the entire meteorite -- both the samples the scientists took, and the much larger piece in Nahum Gardner's yard -- evaporate away completely.  Well, not completely, because it's Lovecraft, after all; it left behind a miasma -- dare I say, an eldritch miasma -- that proceeds to poison the well, the soil of the farm, and the entire Gardner family.  The result is the crops, domestic animals, Nahum and his wife and three children, and finally the homestead itself quite literally falling apart, crumbling into a gray dust that "the wind does not seem to affect."  At the end of the story, the narrator describes the reason he found out about the affair -- he is an engineer hired by the state of Massachusetts to scope out a proposed site for a dam and a reservoir, which would flood "the blasted, withered heath that is all that is left of the old Gardner place" and the surrounding land.  "I shall be glad to see the water come," he says.  "I hope the water will always be very deep -- but even so, I shall never drink it."

*shudder*

The story is quite different from Lovecraft's usual fare of cults and Elder Gods and idols of the Great Cthulhu and so on, and you have to wonder what inspired it.  One thing is pretty likely to be the construction of the Scituate Reservoir in Rhode Island in 1925, near his native Providence, and the much-publicized plans for the Quabbin Reservoir in Massachusetts; but I wonder if he also got the idea from a pair of wild tales that had been all over the news not long before.

The first occurred in 1916 near Bargaintown, New Jersey, where a farmer named Henry Prantl reported something very much like what Nahum Gardner saw in Lovecraft's story -- a white light streaking across the sky, followed by the boom of an impact.  Rushing out to investigate, Henry and his son John found a "writhing piece of mystic material"...

... shaped like a charred human hand.

Poor scientists.  Even back then, every new thing that happened left them "baffled."  You have to wonder how they ever manage to do any science at all, given how much time they spend scratching their heads.  [Image is in the Public Domain]

It was at first too hot to touch, but once it cooled, they were able to examine it.  We find out it was "made of no known material," and was "abnormally light for its size."  At first reluctant to part with it, the Prantls realized what money could be made from such an oddity, and leased it to an amusement park in Atlantic City where it was displayed for several years.  Somewhere along the way it was lost, and the Prantls found their temporary fame and dreams of wealth evaporating as quickly as Nahum Gardner's mysterious meteorite.

Not to be outdone, a gem miner in northern California claimed ten years later that he witnessed another meteorite fall, and this one was even better than a flaming hand; it was a flaming skull.  This is only a year before Lovecraft wrote "The Colour Out of Space," and like the first meteorite, it was all over the news, largely because of the indefatigable efforts by its discoverer, Charles E. Grant, to make sure it got into the headlines and stayed there.  Grant said he'd been told about the fall by a "reputable and well-to-do man," and they went out to retrieve the object.  He wouldn't let anyone see it, but sent a photograph to a reporter named Ben Cline, who dutifully wrote a story about it, ending with the wry comment, "[it has] the shape of a human skull, with depressions suggesting facial organs.  The writer's first-hand knowledge of races inhabiting planets other than Mother Earth is limited, and he hesitates, therefore, from the picture, definitely to place the Butte County visitor in the nebular scheme of things."

It didn't take long for people to connect the New Jersey story to the California one, and suggest that the hand and the skull had come from the same body.  If so, it was a little mysterious (1) why one had fallen ten years before the other, (2) how the unfortunate individual got up there in the first place, and (3) why he was coming down in chunks.

Maybe he had the Nahum Gardner falling-to-pieces syndrome, or something.

In any case, people started frantically looking around to find out if other charred body parts had come crashing to Earth, so they could cash in on the notoriety, but no such luck.  What with the hand getting lost right around the same time, and Grant refusing to show anyone the actual skull -- leading many to surmise that he made the whole thing up -- the only result was a flurry of interest in meteorites and, perhaps, Lovecraft's story.

Myself, I wonder if the "hand" was actually a fulgurite -- a long, branching tube of vitrified and fused soil, sand, and debris left behind when lightning strikes the ground.  Some of these things have a remarkably organic look, and the ones I've seen have a striking resemblance to the Prantl photograph.  This would also explain why it was "abnormally light for its size."  As far as Grant's flaming skull goes -- well, like I've said many times before, if you expect me to believe something, show me the goods or else bugger off.  If there was a meteorite at all -- i.e., if the photograph itself wasn't a fake -- its resemblance to a skull is very likely to be nothing more than a combination of pareidolia and Grant jumping up and down shouting, "It looks like a skull, doesn't it?  Doesn't it?"

So that's today's tidbit of historical weirdness.  Meteoritic body parts and one of Lovecraft's best stories.  I'm happy to report that neither the Scituate nor the Quabbin Reservoir seem to have poisoned anyone, and that I haven't heard any reports out of southern New Jersey or northern California suggesting anybody out there had any difficulties with "colours."

Just as well.  What happened to the Gardner family was nasty.  I wouldn't even wish that on Elon Musk, and that's saying something.

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Impact

New from the "Well, I Guess That's A Silver Lining?" department, we have: a massive meteorite collision 3.26 billion years ago that may have jump-started the evolution of life on Earth.

And I do mean massive.  This particular meteorite, given the unprepossessing name "S2," is estimated to have been a hundred times heavier than the Chicxulub Impactor that wrote finis on the Age of the Dinosaurs around 66 million years ago.  The S2 impact in effect took a chunk of rock four times the size of Mount Everest and slung it toward Earth at the muzzle velocity of a bullet fired from a gun.

The evidence for this impact was found in one of the oldest exposed rock formations on Earth -- the Barberton Greenstone, on the eastern edge of the Kaapvaal Craton in northeastern South Africa.  Geologists found tiny spherules -- microscopic glassy beads that result from molten rock being flung upward and aerosolized.  The impact not only blasted and melted millions of tons of rock, it generated so much heat that it boiled off the upper layer of the ocean, and the liquid water left behind was turned into the mother of all tsunamis.

"Picture yourself standing off the coast of Cape Cod, in a shelf of shallow water," said Nadja Drabon of Harvard University, who led the study.  "It’s a low-energy environment, without strong currents.  Then all of a sudden, you have a giant tsunami, sweeping by and ripping up the seafloor."

[Image is in the Public Domain courtesy of artist Donald Davis]

But this was a very different Earth from the one we currently live on; it's unlikely there was any multicellular life yet, and possibly not even any eukaryotic organisms.

"No complex life had formed yet, and only single-celled life was present in the form of bacteria and archaea," Drabon said.  "The oceans likely contained some life, but not as much as today in part due to a lack of nutrients.  Some people even describe the Archean oceans as ‘biological deserts.’  The Archean Earth was a water world with few islands sticking out.  It would have been a curious sight, as the oceans were probably green in color from iron-rich deep waters...  Before the impact, there was some, but not much, life in the oceans due to the lack of nutrients and electron donors such as iron in the shallow water.  The impact released essential nutrients, such as phosphorus, on a global scale.  A student aptly called this impact a ‘fertilizer bomb.’  Overall, this is very good news for the evolution of early life on Earth, as impacts would have been much more frequent during the early stages of life’s evolution than they are today."

Well, "very good news" for the survivors, I guess, but the life forms caught in the boiling-hot tsunami or the ones that got bombarded by a rain of molten rock spherules might have disagreed.

But being bacteria, their sky-high reproductive rate certainly allowed them to rebound rapidly, especially given that the impact had basically blenderized the oceans, churning up vast amounts of iron- and phosphorus-rich sediments.  This triggered a planet-wide bacterial bloom, and it's likely that once the dust settled, the Archean oceans were once again thriving.  Even though the first eukaryotes were still over a billion years in the future, the stage had been set for the slow progression that would ultimately lead to the tremendous diversification the ended the Precambrian Era.

So even a collision from a piece of rock four times bigger than Everest didn't wipe out all life, which -- as I said earlier -- is, I suppose, the silver lining to all this.  As Ian Malcolm so famously put it, "Life, uh, finds a way."

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Deep impact

Tektites are curious, glassy blobs of rock, from millimeters to centimeters in diameter.  At first thought to be similar to obsidian (volcanic glass), formed when silica-rich lava cools too quickly to form crystals, it soon became apparent that tektites were something else entirely.  They have strangely pitted surfaces, are often teardrop-shaped, and (once such studies became possible) they were found to have an entirely different chemistry than obsidian.  Most puzzling was the fact that tektites are most often found in circumscribed geographical regions nicknamed "strewnfields" -- which usually were nowhere near recently-erupted volcanoes.

It wasn't until the 1920s that geologist Franz Eduard Suess proposed the theory now accepted today, and coined the name tektite (from the Greek τηκτός, "molten").  Tektites form when a meteorite strikes the Earth, liquefying the rock on the surface upon impact.  The molten rock is thrown outward from the blast site, creating the circular or elliptical "strewnfield" -- and explaining why the blobs thus created don't match the chemistry of igneous rock.  Their composition is different depending on the nature of the rock at the location where the meteorite struck.

[Image licensed under the Creative Commons James St. John, Indochinite tektite (Pleistocene, 783-803 ka; Australasian Tektite Strewn Field, southeastern Asia) 4, CC BY 2.0]

So, you'd think once Suess said, "These are formed when a bigass rock slams into the ground" (I paraphrase him slightly), finding the crater where the thing landed would be easy, right?  Just draw a circle around the strewnfield and then look in the middle?

Wrong.

There's a relatively recent strewnfield -- on the order of 790,000 years old, which is a snap of the fingers, geologically speaking -- that is abso-freaking-lutely huge.  It extends from southern China to Antarctica (going north-south) and from the floor of the middle of the Indian Ocean to Micronesia (going west-east).  And that's just where the tektites have been definitively identified.  By some estimates, the Australasian strewnfield might cover thirty percent of the Earth's surface.

But the location of the crater proved elusive.  Part of it is that the center of the strewnfield is in Southeast Asia, which is (mostly) impenetrable jungle, and in places the terrain is so steep and rugged as to be nearly impassable.  But despite the difficulties, geologists have finally located the crater, and also determined why it wasn't obvious despite how recently it occurred.

The Australasian meteorite struck a spot in Laos that already had an active volcano.

The heat from the impact did two things -- flung blobs of molten rock all over the place (the tektites geologists later found in the strewnfield), and also triggered a massive eruption, producing a large enough lava flow to fill in and bury the crater.

[Map from Sieh et al.]

What I find most astonishing about all this is that the impact of this gigantic rock, only 790,000 years ago, didn't cause climatic chaos and a resulting extinction event.  Our relatives, Homo erectus, were living and apparently thriving in southern China both during and after the impact, and seem to have been none the worse for the event.  (If some of them were in Laos, they were probably deep-fried; but given that there was an active volcano there anyhow...) 

I wonder if the reason for the relatively low environmental impact had to do with the geology of the place the meteorite hit, which was primarily made of basalt and other hard igneous rocks.  The Chicxulub strike, 66 million years ago, was devastating not only because it was so big, but because it hit a formation of shallow marine limestone, which literally vaporized on impact, creating a shock wave of superheated water vapor and carbon dioxide that incinerated everything within a radius of a thousand kilometers.  There has to be more to it than simply size; the two weren't that different, an estimated two kilometers in diameter for the Australasian impact and between ten and twelve for Chicxulub.

Whatever the reason was for the difference, it's a good thing for us, because another Chicxulub-type event 790,000 years ago, and we'd very likely not be here.

In any case, it's pretty cool that we can use the splash patterns of molten debris to identify the location of a meteorite impact almost eight hundred thousand years after it happened, despite the fact that the whole thing was filled in with lava and overgrown by jungle.  Further underscoring my bafflement over how anyone can not find science amazingly cool.

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A projectile from deep space

Sometimes the most interesting questions to ask in science are the ones about facts so commonplace that we don't usually even think about them.  For example: how did the Earth end up with the composition it has?

The crust of the Earth -- the part that (obviously) we're most familiar with -- is largely made of silicate rocks (especially feldspars), with a good bit of magnesium, aluminum, potassium, and sodium thrown in.  The mantle, the liquid-to-semisolid bit beneath the crust, is also rich in silicates, but as you go deeper the iron and magnesium content increases (minerals with those elements are generally denser than silicates, so the silicates float to the top).  The core is mainly iron and nickel.

The oceans and atmosphere are a thin layer that is insignificant in terms of contribution to the mass of the Earth as a whole.  (Pretty damn significant to life on Earth, of course.)  And the impressive mountains and valleys, not to mention things like the oceanic trenches, aren't as impressive as they seem from our vantage point.  I remember being blown away when one of my geology professors said that the highest mountain ranges and deepest trenches have less topographic relief than you find on a typical billiard ball.

The Earth formed during the early days of the Solar System from accretion of asteroids, dust, and debris that pulled together from what was probably a set of rings around the Sun similar to what still exists around the planet Saturn.  During that phase, the energy of the constant collisions and bombardment heated the nascent Earth to beyond the melting point of the rock that it was made of, rendering the whole mass molten, glowing orange-hot.  (Some of that heat is what still makes the interior of the Earth hot today; the rest comes from the breakdown of radioactive elements in the core and mantle.  It's what keeps the Earth tectonically active, and the liquid metallic outer core is very likely why our planet has a magnetic field.)

But the specific makeup of the particular rocks that came together early in Earth's history determined what we have here today.  That includes the water in our lakes, rivers, and oceans.  The vast majority of our water arrived during the coalescence of our world -- but we just found out a little more about that particular feature from a much more recent arrival.

On the 28th of February, 2021, a football-sized meteorite streaked across the skies of Winchcombe, a town in Gloucestershire, in the southwest of England.  The intense heating from friction in the atmosphere made the rock explode, and a large chunk of it landed in the driveway of Rob and Cathryn Wilcock, who donated it to the Natural History Museum of London.

Rob Wilcock's photograph of what was left of the Winchcombe meteorite after it smashed into his driveway in February of 2021

The meteorite turned out to be a carbonaceous chondrite, a rare sort of meteorite that is carbon and water-rich.  And the first cool thing was that when the scientists measured the hydrogen-to-deuterium ratio of the the water in the meteorite, they found that it was identical to that in the Earth's oceans.

But you want the kicker?  Also present in the Winchcombe meteorite were various amino acids and a slew of other organic compounds -- the biochemical building blocks of life.

It's discoveries like this that that make me even more certain there's life out there in the cosmos.  Intelligent life is another matter; we still have yet to explain the Fermi paradox (Enrico Fermi's comment that if extraterrestrial life is common, then "where is everybody?" -- a topic about which I wrote in some detail a while back).  But non-technological life?  I'd bet a significant amount of money that it'll turn out to be abundant.  Think of what we could learn from a biology that was entirely separate from us, that had no ancestral connection to anything on Earth.

The mind boggles.

Studies like the one just done on the Winchcombe meteorite give us a perspective not only on how our planet formed, but what else might be out there waiting for us to find.  To quote Carl Sagan: "The universe is a pretty big place.  If it's just us, it seems like an awful waste of space."

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Flotsam and jetsam

One of the topics I keep coming back to here at Skeptophilia is the possibility of extraterrestrial intelligence.  I have to admit, it's a bit of an obsession with me, and has been ever since I watched Lost in Space and the original Star Trek as a kid.

As with so many things, though, this fascination runs headlong into my staunch commitment to rationality, hard evidence, and the scientific method.  The SETI (Search for Extraterrestrial Intelligence) program has, to date, found no particularly good candidates for a signal from an alien race.  The Fermi paradox -- Enrico's famous question that if the likelihood of extraterrestrial life is so high, then "where is everyone?" -- brings us to the rather depressing answer of the three f's, about which I wrote in detail a couple of years ago.

UFO aficionados point toward all of the sightings of alleged alien spacecrafts, and the more skeptical of them rightly insist that even if it's only a small fraction of them that aren't dismissible because of the usual explanations (hoaxes, camera glitches, natural phenomena mistaken for UFOs, etc.), those few are still worth investigating.  Physicist Michio Kaku, who has gained a bit of a reputation for being out in the ionosphere on the topic, said, "You simply cannot dismiss the possibility that some of these UFO sightings are actually sightings from some object created by an advanced civilization… on the off chance that there is something there, that could literally change the course of human history."

But the fact remains that at present we have zero scientifically admissible evidence for the existence of ET. 

Not so fast, says physicist B. P. Embaid, of Central University in Venezuela, in a paper available at arXiv (but not yet peer reviewed).  Embaid has been studying minerals found in meteorites, and he found two -- heideite and brezinaite -- that he says are superconductors that can only be synthesized in a laboratory.

And therefore, the meteorites in which they were found are fragments of a wrecked spaceship.

In Embaid's favor is the fact that heideite and brezinaite are weird minerals, and have never been found in a single natural terrestrial sample.  Brezinaite was created in 1957 by carefully layering chromium and sulfur; heideite eleven years later, by chemically combining chromium, iron, sulfur, and titanium.  Since their first synthesis, both minerals have been found in meteorites, but they have never been seen otherwise, even in ore samples rich in the constituent elements.

So, Embaid says, these are technosignatures -- relics from a technological civilization.

Predictably, my response is:

But I reluctantly must add that I need a good bit more than this to land myself squarely in Embaid's camp.  There's an important word I left out of my statement regarding heideite and brezinaite never showing up in terrestrial samples -- yet.  Recall that the element helium was first discovered on the Sun, from its characteristic spectral lines, long before it was detected in Earth's atmosphere.  I'm also reminded of the discovery in a meteorite of nonperiodic quasicrystals, a form of matter not thought to be naturally occurring anywhere, by a team led by physicist Paul Steinhardt (and which was the subject of his fascinating book The Second Kind of Impossible, which I highly recommend).  It's always tempting to assume that what we know now represents the final, definitive answer, and forget that nature has a way of surprising us over and over.

So could the discovery of two odd superconducting minerals in meteorites mean that we're looking at the flotsam and jetsam of a wrecked extraterrestrial spacecraft?  Sure.  We shouldn't dismiss that possibility simply because the bent of a lot of scientists is to scoff at UFOlogy; that is in itself a bias.  But based on what we currently have, it is way premature to conclude that the anomalous meteorites are technosignatures.  

Now, if a meteorite contained some superconducting materials laid out in a pattern reminiscent of a circuit board, then you might have me convinced.  That, after all, is how the Tenth Doctor figured out what was going on in "The Fires of Pompeii:"

And hey, if a piece of evidence is good enough for the Doctor, it's good enough for me.

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Forensic geology

I've been interested in rocks since I was a kid.  My dad was a rockhound -- more specifically, a lapidary, who made jewelry from such semiprecious stones as turquoise, agate, and jasper.  The high point of my year was our annual trip to Arizona and New Mexico, when we split our time between searching for cool rocks in the canyons and hills of the southwestern desert and pawing through the offerings of the hundreds of rock shops found throughout the region.

Besides the simple beauty of the rocks themselves, it fascinated me to find out that with many rocks, you could figure out how and when they formed.  A lot of the gem-quality rocks and minerals my dad was looking for -- malachite, azurite, and opal amongst them -- are created by slow precipitation of layers of minerals from supersaturated water; others, such as lapis lazuli, rhodonite, and garnets form when metal-bearing rocks are metamorphosed by contact with magma far underground.

[Image licensed under the Creative Commons Olga Semiletova, Минералы горных пород, Creative Commons Attribution-Share Alike 4.0 International license]

Once I found out that the "when" part was also often knowable, through such techniques as radioisotope dating and stratigraphy, it was always with a sense of awe that I held pieces of rock in my hand.  Even around where I live now, where there are few if any of the lovely gem-quality stones you find in the southwest, there's still something kind of mind-boggling about knowing the layers of limestone and shale that form the bedrock here in upstate New York were formed in the warm shallows of a warm ocean during the Devonian Period, on the order of four hundred million years ago.

But if you think that's impressive, wait till you hear about the research out of the University of Johannesburg that was published in the journal Icarus last week.

The research centered around a stone in the desert of western Egypt called Hypatia, given the name by Egyptian geologist Aly Barakat in honor of the brilliant, tragic polymath whose career was cut short when she was brutally murdered by a mob on the orders of Cyril, bishop of Alexandria.  (The aftermath, although infuriating, is typical of the time; Hypatia was largely forgotten, while Cyril went on to be canonized as a saint by the Roman Catholic Church.)  The stone, fittingly considering Hypatia's contributions to astronomy, turns out to be extraterrestrial in origin, later falling as a meteorite to the surface of the Earth.

But "extraterrestrial" is a big place, as it were.  Where exactly did it form?  Chemical tests on the rock found that it didn't match the composition of any known asteroid or comet; then, the mystery deepened when it was found to contain nickel phosphide, which has never been found on any solid material tested in the entire Solar System.

Further tests only made the rock seem more anomalous.  Silicon, second only to oxygen as the most common element in the Earth's crust (a little over 28%, to be exact), was almost absent, as were calcium, chromium, and manganese; on the other hand, there was far more iron, sulfur, phosphorus, copper, and vanadium than you'd expect.  The ratios were far off not only from rocks in our Solar System, they didn't match the composition of interstellar dust, either.

The researchers decided to go at it from the other direction.  Instead of trying to find another sample that matched, they looked at what process would create the element ratios that Hypatia has.  And they found only one candidate that matched.

A type 1a supernova.

Type 1a supernovas occur in binary star systems, when one of the stars is relatively low mass (on the order of the Sun) and ends its life as a super-compact white dwarf star.  White dwarf stars have an upper limit on their mass (specifically about 1.4 times the mass of the Sun) called the Chandrasekhar limit, after Nobel Prize winning astronomer Subrahmanyan Chandrasekhar.  The reason is that at the end of a star's life, when the outward pressure caused by the fusion in the core drops to the point that it can't overcome the inward pull of gravity from the star's mass, it begins to collapse until some other force kicks in to oppose it.  In white dwarf stars, this occurs when the mutual repulsion of electrons in the star's constituent atoms counterbalances the pull of gravity.  In stellar remnants more than 1.4 times the mass of the Sun, electrostatic repulsion isn't powerful enough to halt the collapse.  (The other two possibilities, for progressively higher masses, are neutron stars and black holes.)

In binary stars, when one of the members becomes a white dwarf, the gravitational pull of its extremely compact mass begins to siphon material from its companion.  This (obviously) increases the white dwarf's mass.  Once it passes the Chandrasekhar limit, the white dwarf resumes its collapse.  The temperature of the white dwarf skyrockets, and...

... BOOM.

The whole thing blows itself to smithereens.  Fortunately for us, really; a lot of the elements that make up the Solar System were formed in violent events such as the various kinds of supernovas.  But the models of the relatively rare type 1a (only thought to happen once or twice a century in a typical galaxy of a hundred billion stars) generate a distinct set of elements -- and the percent composition of Hypatia matches the prediction perfectly.

So this chunk of rock in the Egyptian desert was created in the cataclysmic self-destruction of a white dwarf star, probably long before the Solar System even formed.  Since then it's been coursing through interstellar space, eventually colliding with our obscure little planet in the outskirts of the Milky Way.

When I was twelve, holding a piece of billion-year-old limestone from the Grand Canyon, little did I realize how much more amazing such origin stories could get.

I think the real Hypatia would have been fascinated.

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Big geology

It's easy to get overwhelmed when you start looking into geology.

Both the size scale and the time scale are so immense that it's hard to wrap your brain around them.  Huge forces at work, that have been at work for billions of years -- and will continue to work for another billion.  Makes me feel awfully... insignificant.

The topic comes up because of three recent bits of research into just how powerful geological processes can be.  In the first, scientists were studying a crater field in Wyoming that dates to the Permian Period, around 280 million years ago (28 million years, give or take, before the biggest mass extinction the Earth has ever experienced).  The craters are between ten and seventy meters in diameter, and there are several dozen of them, all dating from right around the same time.  The thought was that they were created when an asteroid exploded in the upper atmosphere, raining debris of various sizes on the impact site.

The recent research, though, shows that what happened was even more dramatic.

"Many of the craters are clustered in groups and are aligned along rays," said Thomas Kenkmann of the University of Freiburg, who led the project.  "Furthermore, several craters are elliptical, allowing the reconstruction of the incoming paths of the impactors.  The reconstructed trajectories have a radial pattern.  The trajectories indicate a single source and show that the craters were formed by ejected blocks from a large primary crater."

So what appears to have happened is this.

A large meteorite hit the Earth -- triangulating from the pattern of impact craters, something like 150 and 200 kilometers away -- and the blast flung pieces of rock (both from the meteorite and from the impact site) into the air, which then arced back down and struck at speeds estimated to be up to a thousand meters per second.  The craters were formed by impacts from rocks between four and eight meters across, and the primary impact crater (which has not been found, but is thought to be buried under sediments somewhere near the Wyoming-Nebraska border) is thought to be fifty kilometers or more across.

Imagine it.  A huge rock from space hits a spot two hundred kilometers from where you are, and five minutes later you're bombarded by boulders traveling at a kilometer per second. 

This is called "having a bad day."

[Image licensed under the Creative Commons State Farm, Asteroid falling to Earth, CC BY 2.0]

The second link was to research about the geology of Japan -- second only to Indonesia as one of the most dangerously active tectonic regions on Earth -- which showed the presence of a pluton (a large underground blob of rock different from the rocks that surround it) that sits right near the Nankai Subduction Zone.  This pluton is so large that it actually deforms the crust -- causing the bit above it to bulge and the bit below it to sag.  This creates cracks down which groundwater can seep.

And groundwater acts as a lubricant.  So this blob of rock is, apparently, acting as a focal point for enormous earthquakes.

The Kumano pluton (the red bulge in the middle of the image).  The Nankai Subduction Zone is immediately to the left.

Slipping in this subduction zone caused two earthquakes of above magnitude 8, in 1944 and 1946.  Understanding the structure of this complex region might help predict when and where the next one will come.

If that doesn't make you feel small enough, the third piece of research was into the Missoula Megaflood -- a tremendous flood (thus the name) that occurred 18,000 years ago.

During the last ice age, a glacial ice dam formed across what is now the northern Idaho Rockies.  As the climate warmed, the ice melted, and the water backed up into an enormous lake -- called Lake Missoula -- that covered a good bit of what is now western Montana.  Further warming eventually caused the ice dam to collapse, and all that water drained out, sweeping across what is now eastern Washington, and literally scouring the place down to bedrock.  You can still see the effects today; the area is called the "Channeled Scablands," and is formed of teardrop-shaped pockets of relatively intact topsoil surrounded by gullies floored with bare rock.  (If you've ever seen what a shallow stream does to a sandy beach as it flows into sea, you can picture exactly what it looks like.)

The recent research has made the story even more interesting.  One thing that a lot of laypeople have never heard of is the concept of isostasy -- that the tectonic plates, the chunks of the Earth's crust, are actually floating in the liquid mantle beneath them, and the level they float is dependent upon how heavy they are, just as putting heavy weights in a boat make it float lower in the water.  Well, as the Cordilleran Ice Sheet melted, that weight was removed, and the flat piece of crust underneath it tilted upward on the eastern edge.

It's like having a full bowl of water on a table, and lifting one end of the table.  The bowl will dump over, spilling out the water, and it will flow downhill and run off the edge -- just as Lake Missoula did.

Interestingly, exactly the same thing is going on right now underneath Great Britain.  During the last ice age, Scotland was completely glaciated; southern England was not.  The melting of those glaciers has resulted in isostatic rebound, lifting the northern edge of the island by ten centimeters per century.  At the same time, the tilt is pushing southern England downward, and it's sinking, at about five centimeters per century.  (Fortunately, there's no giant lake waiting to spill across the country.)

We humans get a bit cocky at times, don't we?  We're powerful, masters of the planet.  Well... not really.  We're dwarfed by structures and processes we're only beginning to understand.  Probably a good thing, that.  Arrogance never did anyone any favors.  There's nothing wrong with finding out we're not invincible -- and that there are a lot of things out there way, way bigger than we are, that don't give a rat's ass for our little concerns.

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People made fun of Donald Rumsfeld for his statement that there are "known unknowns" -- things we know we don't know -- but a far larger number of "unknown unknowns," which are all the things we aren't even aware that we don't know.

While he certainly could have phrased it a little more clearly, and understand that I'm not in any way defending Donald Rumsfeld's other actions and statements, he certainly was right in this case.  It's profoundly humbling to find out how much we don't know, even about subjects about which we consider ourselves experts.  One of the most important things we need to do is to keep in mind not only that we might have things wrong, and that additional evidence may completely overturn what we thought we knew -- and more, that there are some things so far out of our ken that we may not even know they exist.

These ideas -- the perimeter of human knowledge, and the importance of being able to learn, relearn, change directions, and accept new information -- are the topic of psychologist Adam Grant's book Think Again: The Power of Knowing What You Don't Know.  In it, he explores not only how we are all riding around with blinders on, but how to take steps toward removing them, starting with not surrounding yourself with an echo chamber of like-minded people who might not even recognize that they have things wrong.  We should hold our own beliefs up to the light of scrutiny.  As Grant puts it, we should approach issues like scientists looking for the truth, not like a campaigning politician trying to convince an audience.

It's a book that challenges us to move past our stance of "clearly I'm right about this" to the more reasoned approach of "let me see if the evidence supports this."  In this era of media spin, fake news, and propaganda, it's a critical message -- and Think Again should be on everyone's to-read list.

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

Catch a falling star

Today's post is a scientific puzzle that -- so far -- doesn't have an answer.

I'm sure you've all had the lovely experience of seeing meteors in the night sky.  Some of you might even have seen meteor showers, when there can be hundreds of "shooting stars" per hour.  Bright as they are, most meteors are the size of a small pebble; the intense light comes from the heating caused by the friction of passage through the atmosphere.  The speed they're traveling determines how fast they heat up, and that's controlled by the angle with which the meteor intersects with the moving Earth; they can be going anywhere between 11 and 72 kilometers per second.

Sometimes, larger chunks of rock strike the Earth.  Sometimes much larger.  The meteor that exploded over Chelyabinsk, Russia in 2013 is estimated to have been around twenty meters in diameter, and to have weighed on the order of 12,000 tons.  The explosion released an energy equivalent of 400 kilotons of TNT, which is about thirty times that released from the atomic bomb that destroyed Hiroshima.  

[Image licensed under the Creative Commons Alex Alishevskikh, 2013 Chelyabinsk meteor trace, CC BY-SA 2.0]

Big rocks are the exception, of course.  Most meteors are tiny... but there are lots of them.  Honestly, I didn't realize how much meteoritic material hits the Earth.  Given how small most of it is, the vast majority of it goes unnoticed.  But the current estimates are that 44,000 kilograms of meteorites land on the Earth every day.  Most of it lands in the oceans (which, after all, cover seventy percent of the Earth's surface), but the rest of it becomes part of the dust that's floating in the air, and that we give virtually no thought to.

The origin of meteors and meteorites (as they're known once they hit the Earth) has always been thought to be random bits of rocky junk left over from the formation of the Solar System; meteor showers mostly come from the passage of the Earth through the orbital paths of comets.  (Comets, being basically big dirty snowballs, partly evaporate with each passage near the Sun, and any particles of rock embedded in the ice get left behind in a trail corresponding to the comet's orbit.)  Because the origin of meteoritic material was thought to be pretty random, the expectation was that even similar types of meteorites would differ in composition, as they'd come from different sources in the asteroid belt and elsewhere.

Well, turns out that isn't true.  A group of scientists led by Birger Schmitz of Lund University set about to study the only meteorites that hang around for a while in the geological record -- chondrites, or stony meteorites.  (The other main type, iron-nickel meteorites, tend to oxidize pretty rapidly once they hit the Earth, so there aren't any particularly old iron-nickel meteorites known.)  Even the chondrites break down and erode, but there's a part of them -- grains of a mineral called chrome spinel -- that are resistant enough to degradation that they can last a billion years essentially unchanged.

So Schmitz's group decided to look at the commonness of meteoritic chrome spinel crystals in the geological record (which would tell them how meteor strike frequency had changed over time), and the specific composition of the crystals (which would tell them the origins of the grains).

And that's when they got a surprise.

Not only has the flux of meteorites barely changed over the entirety of geological history, the composition of the chrome spinel crystals hasn't changed, either -- leading Schmitz et al. to conclude that the vast majority of meteors come from the same, and as yet unidentified, source.

The authors write:

The meteoritic material falling on Earth is believed to derive from large break-up or cratering events in the asteroid belt.  The flux of extraterrestrial material would then vary in accordance with the timing of such asteroid family-forming events.  In order to validate this, we investigated marine sediments representing 15 timewindows in the Phanerozoic for content of micrometeoritic relict chrome-spinel grains (>32 μm).  We compare these data with the timing of the 15 largest break-up events involving chrome-spinel–bearing asteroids (S- and V-types).  Unexpectedly, our Phanerozoic time windows show a stable flux dominated by ordinary chondrites similar to today’s flux.  Only in the mid-Ordovician, in connection with the breakup of the L-chondrite parent body, do we observe an anomalous micrometeorite regime with a two to three orders-of-magnitude increase in the flux of L-chondritic chrome-spinel grains to Earth.  This corresponds to a one order-of-magnitude excess in the number of impact craters in the mid-Ordovician following the L-chondrite break-up, the only resolvable peak in Phanerozoic cratering rates indicative of an asteroid shower.  We argue that meteorites and small (<1-km-sized) asteroids impacting Earth mainly sample a very small region of orbital space in the asteroid belt.  This selectiveness has been remarkably stable over the past 500 Ma.

So as baffling as it seems, it looks like most of the stony meteors out there come from one source -- probably the collision of two asteroids in the very, very distant past.  This impact created a huge cloud of fragments of different sizes but of relatively uniform composition, and that's the stuff that's been raining down on Earth for the past billion years.

Think about that next time you see a "falling star" on a clear, cloudless night.  You're seeing a relic of a collision that occurred back when the vast majority of living things were single-celled creatures living in the ocean.  That little pebble creating a streak of light across the sky has been floating around in space ever since, finally intersecting Earth's path and burning up in the atmosphere.

Just in time for you to make a wish.

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I'm in awe of people who are true masters of their craft.  My son is a professional glassblower, making precision scientific equipment, and watching him do what he does has always seemed to me to be a little like watching a magic show.  On a (much) lower level of skill, I'm an amateur potter, and have a great time exploring different kinds of clays, pigments, stains, and glazes used in making functional pottery.

What amazes me, though, is that crafts like these aren't new.  Glassblowing, pottery-making, blacksmithing, and other such endeavors date back to long before we knew anything about the underlying chemistry and physics; the techniques were developed by a long history of trial and error.

This is the subject of Anna Ploszajski's new book Handmade: A Scientist's Search for Meaning Through Making, in which she visits some of the finest craftspeople in the world -- and looks at what each is doing through the lenses of history and science.  It's a fascinating inquiry into the drive to create, and how we've learned to manipulate the materials around us into tools, technology, and fine art.

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

The left-handed universe

I first ran into the concept of chirality when I was a fifteen-year-old Trekkie science fiction nerd.

I grew up watching the original Star Trek, which impressed the hell out of me as a kid even though rewatching some of the episodes now generates painful full-body cringes at the blatant sexism and near-jingoistic chauvinism.  Be that as it may, after going through the entire series I don't even know how many times, I started reading some of the fan fiction.

The fan fiction, of course, was more uneven than the show had been.  Some of it was pretty good, some downright terrible.  One that had elements of both, putting it somewhere in the "fair to middling" category, was Spock Must Die by James Blish.  Blish had gotten into the Star Trek universe writing short-story adaptations of most of the original series episodes, but this one was entirely new.

Well, mostly.  It springboarded off an original series episode, "Errand of Mercy," in which the Federation and the Klingons are fighting over the planet Organia, which is populated by a peaceful, pastoral society.  Kirk et al. are trying to stop the Klingons from massacring the Organians, but much to Kirk's dismay, the Organians refuse Federation protection, insisting they don't need any help.  And it turns out they don't -- in the end, you find out that the Organians are super-powerful aliens who only assumed human-ish form to communicate with the two humanoid invading forces, and are so far beyond both of them that they indeed had nothing to fear.

In Spock Must Die, the crew of the Enterprise is sent to investigate why Organia has suddenly gone radio-silent.  It turns out that the Klingons have surrounded the entire planet with a force field.  Spock volunteers to try to transport through it, which fails -- but after the attempt, suddenly there are two Spocks in the transporter room, each claiming to be the real, original Vulcan.

[spoiler alert, if anyone is actually going to go back and read it...]  What happened is that the transporter beam was reflected off the surface of the force field, and it duplicated Spock -- there was the original (who never left the transporter pad) and the duplicate (the reflection, recreated in place).  Since both the original and the duplicate were identical down to the last neuron, each of them had the same memories, and each was convinced he was the real Spock.

The key turned out to be the fact that the duplicate had been reflected all the way down to the molecular level.

Why this matters is that a number of molecules in our bodies -- amino acids and sugars being two common examples -- are chiral, meaning they have a "handedness."  Just like a glove, they exist in two possible forms, a "right-handed" and a "left-handed" one, which are mirror images of each other.  And for reasons unknown, all of our amino acids are left-handed.  No organism known manufactures right-handed amino acids.  Further, if you synthesized right-handed amino acids -- which could be done in the laboratory -- and fed them to a terrestrial organism, the organism would starve.

But the reflected Spock, of course, is exactly the opposite.  Kirk eventually figures out what's happened because one of the Spocks barricades himself in one of the science laboratories, claiming the other Spock wants to kill him.  The truth was he had to have access to a lab in order to synthesize the right-handed amino acids without which he'd die.

Clever concept for a story, right there.

[Image licensed under the Creative Commons Petritap, Finnish mittens, CC BY-SA 3.0]

Chirality is quite a mystery.  Like I said, the left-handedness of amino acids is shared by all known terrestrial organisms, so that bias must have happened very early in the generation of life.

Why it happened is another matter entirely.  A persistent question in scientific inquiries into the origin of life on Earth (and the possibility of life elsewhere) is how much of our own biochemistry and metabolism is constrained.  We code our genetic information as DNA; could it be done a different way elsewhere?  Our primary energy driver is ATP.  Are there other ways organisms might store and access chemical energy?  The question of constraint goes all the way up the scale to macroscopic features, such as cephalization -- the clustering of the sensory processing organs near the anterior end of the animal.  Makes sense; you want your sensors facing (1) the direction you're traveling, and (2) what you're eating.  But are there other equally sensible ways to put an animal together?

Some things we take for granted almost certainly aren't constrained, like bilateral symmetry.  So many animals are bilaterally symmetrical that the ones that aren't (like adult flounders) stand out as bizarre.  Aficionados of H. P. Lovecraft might remember that amongst the innovative ideas he used was that the aliens in "At the Mountains of Madness" weren't bilateral, but had five-way symmetry -- something completely unknown on Earth.  (You may be thinking, "wait... starfish?"  Starfish have what I'd call pseudo-pentaradial symmetry.  As larvae, they're clearly bilateral, and they lose a lot of bilateral features when they mature.  But some characteristics -- like the position of the sieve plate, their water-intake device -- give away that deep down, they are still basically bilateral.)

Anyhow, all this comes up because of a recent discovery by astrobiologists at NASA's Goddard Space Flight Center.  In a press release, we hear about a meteorite discovered in Antarctica called Asuka 12236, which is a carbonaceous chondrite -- a peculiar type of meteorite that is rich in organic compounds.  Asuka 12236 contained large quantities of amino acids, which isn't as bizarre as it sounds; amino acids have been shown to form relatively easily if there are raw materials and a source of energy.

What stands out is that all of the amino acids in Asuka 12236 are left-handed -- just like the ones on Earth.

The scientists studying the meteorite are up front that the first thing to do is rule out that the amino acids in the meteorite aren't contaminants absorbed after the rock crash-landed.  Most of the experts, however, think this is unlikely, and that we're looking at a genuine sample of extraterrestrial amino acids.  And the fact that they all show left-handed chirality is pretty remarkable -- suggesting that the chirality of our biochemicals might, in fact, be constrained, and that we could well find biochemistry similar to our own on other planets.

In that way, at least.

So that's one less thing to worry about if we ever go to an alien world.  Unlike the right-handed reflected Mr. Spock, we'd be able to metabolize alien amino acids just fine.

Of course, how familiar-looking everything else would be is still open to question.

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This week's Skeptophilia book recommendation of the week is a brilliant retrospective of how we've come to our understanding of one of the fastest-moving scientific fields: genetics.

In Siddhartha Mukherjee's wonderful book The Gene: An Intimate History, we're taken from the first bit of research that suggested how inheritance took place: Gregor Mendel's famous study of pea plants that established a "unit of heredity" (he called them "factors" rather than "genes" or "alleles," but he got the basic idea spot on).  From there, he looks at how our understanding of heredity was refined -- how DNA was identified as the chemical that housed genetic information, to how that information is encoded and translated, to cutting-edge research in gene modification techniques like CRISPR-Cas9.  Along each step, he paints a very human picture of researchers striving to understand, many of them with inadequate tools and resources, finally leading up to today's fine-grained picture of how heredity works.

It's wonderful reading for anyone interested in genetics and the history of science.

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