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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The barrage

At the last Tompkins County Friends of the Library Used Book Sale, I picked up a copy of Donald Yeomans's fascinating book titled Near-Earth Objects (which has the rather alarming subtitle, Finding Them Before They Find Us).  Yeomans has impeccable credentials -- senior fellow with NASA's Jet Propulsion Laboratory, manager/supervisor of the Near-Earth Object Program Office and Solar System Dynamics Group, and researcher with the Deep Impact Project that investigates the composition, origins, and trajectories of comets.  His book is about the potential for a significant asteroid or comet strike on Earth -- and, more importantly, how we might find potentially hazardous orbiting objects soon enough to have a chance to avert the collision.

As Canadian astronaut Chris Hadfield put it, "The dinosaurs went extinct because they didn't have a space program."

One of the topics in Yeomans's book is the history of impacts, including the famous one that ended the Mesozoic Era.  But his timeline goes back a great deal further than that; one of the sections is devoted to a period called the Late Heavy Bombardment -- on the order of four billion years ago -- during which it is thought that the Earth got absolutely pummeled.

What caused this barrage?  Well, first of all, it must be stated that not all scientists even think it happened.  The geological processes on the Earth's surface have erased most of the evidence.  Studies of cratering on the Moon (which presumably would also have gotten clobbered during the same period) have yielded conflicting results; Patrick Boehnke and Mark Harrison, of the University of California, wrote a paper back in 2016 suggesting that the radioisotope dating of rocks from the Moon supported a uniformly decreasing impact rate over its history (i.e., no sudden spike about four billion years ago).

Other researchers disagree.  Three of the largest impact basins on the Moon, the Mare Imbrium, Mare Serenitatis, and Mare Nectaris, all appear to date from right around the time of the hypothesized bombardment.  If the same happened on Earth, it was cataclysmic -- turning large areas of the Earth's crust into molten lava, and vaporizing huge volumes of water in the early oceans.

[Image licensed under the Creative Commons CC-BY-SA, from https://ancient-life-and-history-earth.fandom.com/wiki/Late_Heavy_Bombardment]

Where it gets interesting is the explanation for why the Late Heavy Bombardment happened -- if it did.  The whole thing hinges on a bit of physics that falls into the "stuff that I theoretically knew, but never really thought about" department.

The orbital path of a planet (or asteroid, or comet, or whatever) remains stable as long as nothing adds or removes energy from it.  If something subtracts energy, the orbit becomes smaller; if something adds energy, the orbit gets bigger.  Enough added energy, and it achieves escape velocity and is ejected from the system altogether.  But what would itself have enough energy to interact with something the size of a planet in such a way as to make any difference?

Back in the early history of the Solar System, there was a clutter of debris left over from its formation.  We still have three major bands of it left -- the Asteroid Belt between Mars and Jupiter, the Kuiper Belt beyond the orbit of Neptune, and the Oort Cloud way out past the orbit of Pluto.  There are few asteroids left in the vicinity of the planets, because any that were there were swept up gravitationally.  In fact, that's one of the requirements for an object to be classified as a planet; that it clear the space near it of asteroids.  (This is the characteristic that caused Pluto to get demoted.)

But four billion years ago, there was a great deal more debris around.  Any large-ish asteroids that got near a planet resulted in their giving a gravitational yank on each other; if the asteroid was ahead of the planet, it had a bit of its energy stolen by the planet (making the planet's orbital axis get bigger); if it passed behind the planet, the reverse happened (making the planet's orbital axis shrink).  Well, according to the models described by Yeomans, eventually the pushing and pulling by all of the asteroids added up, and a curious thing happened.

The two largest planets, Jupiter and Saturn, had their orbits altered until they were in a highly stable configuration called a 2:1 orbital resonance.  

What this means is that they were in a pattern where Saturn's orbital period was exactly twice Jupiter's.  (They're still close to that; Saturn orbits the Sun once every 29.4 years, and Jupiter once every 11.9 years.)  But when they were in perfect 2:1 resonance, they reinforced each other's gravitational influence on the outer planets, Uranus and Neptune, giving them a kick every time they lined up -- a little like a kid on a playground swing kicking off every time they pass the ground.

This did two things.  First, it gave energy to Uranus and Neptune, making their orbits bigger, moving them outwards.  Second, it subtracted energy from Jupiter and Saturn, making their orbits smaller (and eventually destroying the resonance).  But the important one here is Neptune, because the increase of its orbit moved it out into a region of space that hadn't been cleared of debris.  When Neptune slipped outward into the inner Kuiper Belt, around four billion years ago, this had the effect of slingshotting a great deal of that debris into the inner Solar System...

... turning Earth into a gigantic bullseye for meteor strikes.

So it's fascinating that if the Late Heavy Bombardment actually did occur, there's a good model for what might have caused it.

The good news is that now that Jupiter and Saturn are no longer in resonance, Neptune is more or less staying put, so any further target practice is unlikely.  Doesn't mean we're out of the woods completely, of course.  Yeomans's whole book is about the possibility of asteroid strikes.

But at least it looks like the barrage is a thing of the past.

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Missing the target

Lately I've been seeing a lot of buzz on social media apropos of the Earth being hit by a killer asteroid.

Much of this appears to be wishful thinking.

Most of it seems to focus on the asteroid 2007 FT3, which is one of the bodies orbiting the Sun that is classified as a "near-Earth object" -- something with an orbit that crosses Earth's, and could potentially hit us at some point in the future.  It bears keeping in mind, however, that even on the scale of the Solar System, the Earth is a really small target.  This "deadly asteroid," we're told, is "on a collision course with Earth" -- but then you find out that its likelihood of its actually striking us on the date of Doomsday, March 3, 2030, is around one in ten million.

Oh, but there's "an altogether more sinister estimate" that 2007 FT3 could hit us on October 5, 2024, but the chances there are one in 11.5 million.  Why this is "altogether more sinister," I'm not sure.  Maybe just because it's sooner.  Or maybe the author of the article doesn't understand how math works and thinks that the bigger the second number, the worse it is.  I dunno.

Then there's the much-hyped asteroid 99942 Apophis, which was first thought to have a 2.7% chance of hitting the Earth in April of 2029 (more accurate observations of its orbit eliminated that possibility entirely), and then gets a second shot at us in April of 2036.  The 2036 collision depends on it passing through a gravitational keyhole during its 2029 close approach -- a tiny region in space where the pull of a much larger planet shifts the orbit of a smaller body in such a way that they then collide on a future pass.  Initially, the keyhole was estimated to be eight hundred kilometers in diameter, and this caused the physicists at NASA to rate Apophis at a four out of ten on the Torino Impact Scale -- the highest value any object has had since such assessments began.  (A rating of four means "A close encounter, meriting attention by astronomers.  Current calculations give a 1% or greater chance of collision capable of regional devastation.  Most likely, new telescopic observations will lead to reassignment to Level 0.  Attention by public and by public officials is merited if the encounter is less than a decade away.")  If it hit, the impact site would be in the eastern Pacific, which would be seriously bad news for anyone living in coastal California.

The close approach in 2029 [Image licensed under the Creative Commons Phoenix7777, Animation of 99942 Apophis orbit around Sun, CC BY-SA 4.0]

This, of course, spurred the scientists to try to refine their measurements, and when they did -- as the scale suggested -- they found out we're not in any danger.  The gravitational keyhole turns out to be only a kilometer wide, and Apophis will miss it completely.

In fact, there are currently no known objects with a Torino Scale rating greater than zero.

It's always possible, of course, that we could be hit out of the blue by something we never saw coming.  But given that we're talking about an unknown risk from an unknown object of unknown size hitting in an unknown location at an unknown time, I think we have more pressing things to worry about.  Sure, something big will eventually hit the Earth, but it's not going to happen in the foreseeable future.  NASA and the other space monitoring agencies in the world are doing a pretty good job of watching the skies, so maybe we should all just turn our attention on more important matters, like trying to figure out how nearly half of Americans think the best choice for president is a multiply-indicted, incompetent compulsive liar who shows every sign of incipient dementia.

In any case, I'm not concerned about asteroid impacts, and all the hype is just more clickbait.  So if you live on the West Coast and were planning on moving inland, or are considering cancelling your plans for a big Halloween bash this year, you probably should just simmer down.

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The cities on the plain

Scary place, this universe of ours.

I've dealt here before with some cosmic-level catastrophes -- supernovas and Wolf-Rayet stars and black holes and gamma-ray bursters and false vacuums -- but the situation's not much better down here on the seemingly peaceful surface of the Earth.  There are weather-related disasters like hurricanes and tornadoes, as well as spectacular but less-known phenomena such as convective microbursts, which are not only scary and violent but strike seemingly out of nowhere, producing wind that goes from dead calm to 120 kilometers per hour in under two minutes (and are over equally quickly).  Volcanoes and earthquakes are seldom a surprise with regards to location, but are unpredictable in terms of timing -- although now with better remote sensing techniques, we're getting more accurate at forecasting quakes and eruptions, such as the one currently devastating the island of La Palma in the Canary Islands.  (The Ministry of Tourism announced that the island is "still open to tourism," adding, "You must have a valid passport, as well as proof that you are a complete idiot.")

So we're better off than the people in Pompeii in 79 C.E., or the poor folks in 1902 who were the victims of a pyroclastic eruption from Mont Pelée in Martinique, which killed thirty thousand people in less than five minutes.  There were only three known survivors, the most famous of which was in an underground jail cell at the time.  All three escaped with burns and other injuries, but at least didn't get flash-fried like the rest of the city.

I'm pretty lucky here in upstate New York.  We're not in an earthquake zone, even farther from the nearest volcano, very rarely have tornadoes, and although we sometimes get sideswiped by the remnants of an Atlantic hurricane, we seldom get anything serious.  The worst we have to contend with is snow, but even our worst storms (like the "Hundred-Year Storm" of  March 1993, eight months after I moved here from Seattle, Washington, which dropped almost two meters of snow on us in a space of 48 hours) are nowhere near as violent as the killer blizzards they get in the Rocky Mountain states and the upper Midwest.

So I can't complain.  Even though I do sometimes anyhow.

But I guess even in a relatively clement place, you never know what's going to hit you.  Sometimes literally, to judge by a paper this week in Nature by a team led by geologist Ted Bunch of Northern Arizona University, which describes the fate of the city of Tall el-Hammam in the southern Jordan Valley. 

Never heard of it?  Neither had I, which is surprising considering both its prominence and its ultimate fate.  Up till about 1650 B.C.E., Tall el-Hammam was the bustling center of commerce for a region inhabited by an estimated fifty thousand people.  

The authors describe it as follows:

The three largest settlements in this area were Tall el-Hammam [TeH], Tall Nimrin, and Jericho (aka, Tell Es-Sultan), urban anchors of three city-state clusters, each surrounded by numerous smaller satellite towns and villages.  At 36 hectares of fortifications (0.36 km2) and an additional 30 hectares of “suburban sprawl,” TeH at its zenith was > 4× larger than Tall Nimrin and > 5× larger than Jericho, and thus, was likely to have been the area’s politically dominant MBA [Middle Bronze Age] urban center for many centuries.  TeH was initially occupied during the early Chalcolithic Period (~ 6600 cal BP) and was a well-established fortified urban center by the Early Bronze Age (~ 5300 cal BP).  The city reached its peak of hegemony during the MBA and dominated the eastern half of the Middle Ghor and most likely, the western half as well.

Then -- suddenly -- the entire city was wiped off the map.  The entire region was abandoned for over six hundred years, and in fact wasn't substantially recolonized for almost a millennium.

So what happened? 

Bunch et al. believe they've figured it out.  In 1650 B.C.E., Tall el-Hammam was flattened -- by a stratospheric meteorite explosion.

Artist's conception of what the original palace at Tall el-Hammam looked like -- and what's left of it

You may recall the 2013 Chelyabinsk meteor, an object an estimated twenty meters across that exploded about thirty kilometers above the surface of the Earth, creating a shock wave that damaged houses and injured an estimated 1,491 people.  The 1908 Tunguska Event was even larger, caused by an object an estimated fifty meters across, and blew down trees radially outward from ground zero, destroying over two thousand square kilometers of forest that were (fortunately) far away from any densely-occupied areas.

The one that destroyed Tall el-Hammam is estimated to be larger still -- the researchers suggest a diameter of around seventy meters.  Tall el-Hammam was, quite literally, blown away, the thick walls of the palace sheared off at the foundation.  Mud bricks and roofing clay actually melted.  Mineralogical analysis of the rocks and debris show something kind of terrifying; inclusions of high-melting-point materials like platinum, iridium, and zircon melted as well, indicating temperatures above 2,000 C (and thus ruling out such causes as city-wide conflagrations, which don't get anywhere near that hot).  Quartz granules in the rocks of the area have radial fracture patterns similar to the circular cracks in your windshield when it's hit by a flying piece of gravel, indicating that something big punched the site.

Really hard.

The researchers suggest that the meteor strike at Tall el-Hammam might have been the origin of the biblical story of the destruction of "the Cities on the Plain," most famously Sodom and Gomorrah, although the jury's still out on that.  It would certainly explain the suddenness and totality of the destruction described in the biblical account, although it'd still leave up in the air why Lot's wife turned into a pillar of salt.

As an aside, the meteor strike in 1650 B.C.E. is not considered a possible basis of the biblical account of the destruction of Jericho, in Joshua chapter 6; by what we know of the chronology of the history of Judea, the Book of Joshua was written nearly a thousand years later.  And it's worth mentioning that there seems to be no evidence whatsoever of Jericho experiencing a catastrophic collapse (the Bible talks about the walls of the city "falling flat") during that entire time period, leading archaeologist and biblical scholar William Dever to state that the story of the fall of Jericho was "invented from whole cloth" as nationalist propaganda by the leaders of the state of Judah to bolster their reputation as not only the Chosen Ones of God, but as all-around tough motherfuckers.  (I paraphrase Dever's actual analysis slightly.)

Anyhow, the Bunch et al. paper is a tour de force of thorough scientific investigation, and from my (admitted layperson's) perspective, it seems like they've locked down their case pretty tightly.  So now you have something else to worry about, even if (like me) you're far away from raging volcanoes, earthquake zones, and Tornado Alley, not to mention any local gamma-ray bursters and black holes.  Exploding rocks from space.  At least it'd be a quick way to go; considering the level of destruction they describe at Tall el-Hammam, we're talking "loud noise and bright light, look upward for a second, then get blasted to smithereens."

Have a nice day.

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Have I got a book for you.

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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!]

Astronomical Whack-a-Mole

Because we all clearly needed something else to worry about, today we have: the mega-asteroids of doom.

This comes up because of a new program at NASA, now that the Trump administration has freed them from the necessity of worrying about climate change.  Called the "Large Synoptic Survey Telescope," this project involves building a huge telescope in Chile that will be looking for "potentially hazardous asteroids" (PHAs).  The idea is that they'll scan the sky looking for any hitherto-unrecorded astronomical object that shows apparent movement against the background stars in an hour.  "Anything that moves in just one hour," writes project leader Michael Lund, astrophysicist at Vanderbilt University, "has to be so close that it is within our Solar System."

It's not like this is an inconsequential threat.  Barringer Crater, in northern Arizona, is a huge hole in the ground that was caused by collision with a nickel-iron meteorite fifty meters in diameter.  The Chesapeake Bay Impact Event, about 35 million years ago, is 85 kilometers across, and was caused by an object about three kilometers wide -- the impact was enough to cause a tsunami that hit the Blue Ridge Mountains.  The mother of 'em all, though, is the 150 kilometer wide Chicxulub Crater, 66 million years ago, which blew up a layer of dust that settled out as clay all over the Earth -- and is thought to have kicked off the Cretaceous Extinction, the final straw for the dinosaurs (except for the ones who were the ancestors of modern birds).

What is cheering, however, is that these events aren't frequent.  The Chelyabinsk meteor of 2013, which exploded 32,000 meters above the Earth's surface but still was able to generate a shock wave big enough to injure 1,200 people.  The object that caused the blast is thought to have been about twenty meters across -- nothing compared to Chesapeake Bay and Chicxulub, but still a little on the scary side.

[Image courtesy of NASA/JPL]

No one doubts that there are lots of objects out there that could potentially play Whack-a-Mole with the Earth.  The LSST gives us hope of finding them before they find us.  The unfortunate part, however, comes when Lund addresses the question of what we could do about it if we discovered that a huge rock was on a collision course with Newark:

If an asteroid is on a collision course hours or days before it occurs, the Earth won’t have many options.  It’s like a car suddenly pulling out in front of you. There is little that you can do.  If, however, we find these asteroids years or decades before a potential collision, then we may be able to use spacecraft to nudge the asteroid enough to change its path so that it and the Earth don’t collide. 

This is, however, easier said than done, and currently, no one really knows how well an asteroid can be redirected.  There have been several proposals for missions by NASA and the European Space Agency to do this, but so far, they have not passed early stages of mission development.

 So it looks like if you found out that day after tomorrow, your home town was going to get clobbered, you'd have two options: (1) get in your car, drive like hell, and hope for the best; or (2) put your head between your legs and kiss your ass goodbye.  I suppose that's better than nothing, especially considering that the alternative is thinking you're going to take a nice nap in your hammock and instead getting vaporized by an enormous superheated rock.

But even so, there's the problem of what it's going to be like for the rest of the Earth, the ones not in the impact zone.  Any impact -- even a relatively small one, like the one that formed Barringer Crater -- is actually going to have an enormous effect even on very distant places, just from the standpoint of kicking up a crapload of dust.  (Recall that when the volcano Tambora erupted in 1815, it caused "the Year Without a Summer," during which crops froze in mid-July and hundreds of thousands of people died of starvation.)

Nearer to the impact site, things get even worse.  Consider the Chelyabinsk meteor, which by comparison is a popgun -- not to mention the fact that it self-destructed 32,000 meters up, and never hit the surface.  The shock wave would be astronomical.  Pun intended.  Closer still, and the heat blast would flash-fry anything in its way.

You don't even get a pass if the impact is in the ocean, because then you've got hundred-foot-high tsunamis to worry about.

So yeah.  Not fun.

The best-case outcome, here, is that Lund and his colleagues scan the sky with the LSST for a while, and say, "Welp.  Nothing much out there.  I guess everything's hunky-dory.  As you were."  Or, that any projected impact will take place thousands of years from now.  (I figure that anyone around then will just have to fend for themselves.)  Or, perhaps, that we could use our technology to redirect the asteroid away from colliding with us.  Lund says this is already being looked into:

The B612 Foundation, a private nonprofit group, is also trying to privately raise money for a mission to redirect an asteroid, and they may be the first to attempt this if the government space programs don’t.  Pushing an asteroid sounds like an odd thing to do, but when we one day find an asteroid on a collision course with Earth, it may well be that knowledge that will save humanity.

I'll be watching the results, though, because being a little on the anxious, neurotic side, I definitely need another thing to keep me up at night.  On the other hand, it's at least temporarily taken my mind off all the other problems we're facing.  Which is good, right?

Of course right.

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This week's book recommendation is from one of my favorite writers and documentary producers, Irish science historian James Burke.  Burke became famous for his series Connections, in which he explored the one-thing-leads-to-another phenomenon which led to so many pivotal discoveries -- if you've seen any of the episodes of Connections, you'll know what I mean when I say that it is just mindblowing fun to watch how this man's brain works.  In his book The Pinball Effect, Burke investigates the role of serendipity -- resulting in another tremendously entertaining and illuminating read.

Farts, craters, Mick Jagger, and the problem with lousy science reporting

One of the reasons that it is critical that we all be science-literate is because it is becoming increasingly apparent that the popular media either (1) hires reporters that aren't, or (2) values getting people to click links over accurate reporting.

I suspect it's (2), honestly.  The most recent examples of this phenomenon smack of "I don't care" far more than they do of "I don't know."  Just in the last week, we've had three examples of truly terrible reporting in media outlets that should have higher standards (i.e., I'm not even considering stuff from The Daily Mail).

And, for the record, this doesn't include the recent hysterical reporting that melting roads in Yellowstone National Park mean that the supervolcano is going to erupt and we're all going to die.

The first one, courtesy of the Australian news outlet News.Com.Au, pisses me off right from the outset, with the title, "A Mysterious Crater in Siberia Has Scientists Seeking Answers."  Because seeking answers isn't what scientists do all the time, or anything.  Then, right in the first line, we find out that they're not up to the task, poor things:  "Scientists baffled by giant crater... over northern Siberia -- a region notorious for devastating events."

"Baffled."  Yup, that's the best they can do, those poor, hapless scientists.  A big hole in the ground appears, and they just throw their hands up in wonderment.

Before we're given any real information, we hear some bizarre theories (if I can dignify them by that name) about what could have caused the hole.  UFOs are connected, or maybe it's the Gates of Hell, or perhaps the entry to "the hollow Earth."  Then they bring up the Tunguska event, a meteor collision that happened in 1908, and suggest that the two might be connected because the impact happened "in the region."

Despite the fact that the new crater is over a thousand miles from the Tunguska site.  This, for reference, is about the distance between New Orleans, Louisiana and Albuquerque, New Mexico.

Only after some time are we told that the Siberian crater site is also the site of a natural gas field in which explosions have taken place before.  In fact, the whole place is pocked with circular craters, probably caused by methane explosions from the permafrost -- i.e., it's a completely natural phenomenon that any competent geologist would have been able to explain without even breaking a sweat.


But this is world-class journalism as compared to ABC News Online, which just reported that Brazil got knocked out of the FIFA World Cup because of Mick Jagger's support.

To be fair, ABC News wasn't intending this as science reporting, but from all evidence, they did take it seriously.  Here's an excerpt:

It seems the Rolling Stone frontman has developed a reputation for jinxing whatever team he supports. Some Brazilian fans are even blaming Jagger for their team’s 7-1 thrashing by Germany in Tuesday’s semifinal game. 

The 70-year-old singer turned up at the game with his 15-year-old son by Luciana Giminez, a Brazilian model and celebrity. Though he wore an England cap, his son was clad in Brazil jersey and they were surrounded by Brazil supporters. 

The legend of the “Jagger Curse” dates back to the 2010 World Cup in South Africa, where he sat next to Bill Clinton for the USA-Ghana match, only to see the U.S. lose 2-1. When he attended the England-Germany game the next day, wearing an England scarf, his home country lost. But it wasn’t until the Dutch defeated Brazil during the quarterfinal round, where Jagger turned up in a Brazil shirt, that the Brazilians first blamed him for the loss.

Seriously?  It couldn't be that the winning team played better, could it?  You know, put the ball into the net more times?

It has to be Mick Jagger's fault?  Because of a magical jinx?


So I'm just going to leave that one sitting there, and move on to the worst example, which has been posted about five million times already on Facebook, to the point that if I see it one more time, I'm going to punch a wall.  I'm referring, of course, to the earthshatteringly abysmal science reporting that was the genesis of The Week's story "Study: Smelling Farts May Be Good For Your Health."

[image courtesy of the Wikimedia Commons]

I'm hoping beyond hope that most of the people who posted this did so not because they believed it, but because most of us still don't mind a good har-de-har over flatulence.  But the story itself is idiotic.  Here's the first paragraph:

The next time someone at your office lets out a "silent but deadly" emission, maybe you should thank them. A new study at the University of Exeter in England suggests that exposure to hydrogen sulfide — a.k.a. what your body produces as bacteria breaks down food, causing gas — could prevent mitochondria damage. Yep, the implication is what you're thinking: People are taking the research to mean that smelling farts could prevent disease and even cancer.

Well, at the risk of sounding snarky, any people who "take this research" this way have the IQ of cheese, because two paragraphs later in the same article the writer says what the research actually showed:

Dr. Matt Whiteman, a University of Exeter professor who worked on the study, said in a statement that researchers are even replicating the natural gas in a new compound, AP39, to reap its health benefits. The scientists are delivering "very small amounts" of AP39 directly into mitochondrial cells to repair damage, which "could hold the key to future therapies," the university's statement reveals.

There is a difference between smelling a fart and having small amounts of dissolved hydrogen sulfide enter the mitochondria of your cells.  It is like saying that because sodium ions are necessary for proper firing of the nerves, that you'll have faster reflexes if you put more salt on your t-bone steak.  Worse than that; it's like saying that you'll have faster reflexes if you snort salt up your nose.

I know that media outlets are in business to make money, and that readers = sponsors = money.  I get that.  But why do we have a culture where people are so much more interested in spurious nonsense (or science that gets reported that way) than they are in the actual science itself?  Has science been portrayed as so unutterably dull that real science stories are skipped in favor of glitzy, sensationalized foolishness?

Or is it that we science teachers are guilty of teaching it that way, and convincing generations of children that science is boring?

Whatever the answer is to that question, I firmly believe that it's based on a misapprehension.  Properly understood, the science itself is cool, awe-inspiring, and fascinating.  Okay, it takes a little more work to understand mitochondria than it does to fall for "sniffing farts prevents cancer," but once you do understand what's really going on, it's a hell of a lot more interesting.

Oh, and it has one other advantage over all this other stuff: it's true.