Blowing bubbles

After Monday's post, about the bizarre hypergiant star Stephenson 2-18, a reader commented, "If you think that's weird, look up 'Fermi bubbles.'"

So I did.  And... yeah.

Discovered back in 2010, the Fermi bubbles -- so named because they were discovered by NASA's Fermi Gamma-ray Telescope -- are a pair of nearly perfectly symmetrical bubbles of high-intensity gamma rays positioned above and below the galactic plane of the Milky Way.  They're huge; each one has a diameter of about 23,000 light years.

False-color image of the Fermi bubbles.  The Milky Way is seen edge-on, running across the middle of the photograph.  [Image is in the Public Domain courtesy of NASA/Goddard Space Flight Center]

Back in 2015, the Fermi bubbles were still completely unexplained, and in fact made #1 in Astronomy magazine's list of "The Fifty Weirdest Objects in the Universe."  That they had something to do with Sagittarius A*, the enormous black hole at the center of the galaxy, seemed like a reasonable guess; but what could create something with such a peculiar figure-eight shape was unknown.

A team led by astrophysicist Rongmon Bordoloi of the Massachusetts Institute of Technology, however, has a model to explain them.  Something around nine million years ago -- not really that far back, in the grand scheme of things -- Sagittarius A* pulled in an enormous cloud of gas and dust.  The origin of that dust cloud is uncertain, but what happened after it got caught is all too clear.  Most of it undoubtedly took the one way trip past the event horizon, but some of it was spun so fast by the black hole's rotation and the resultant twisting of space-time that it gained enough momentum to escape along Sagittarius A*'s spin axis -- i.e., perpendicular to the galactic plane.

This not only accelerated the gas to an unimaginable two million miles an hour, it heated it -- at its edges to just shy of ten thousand degrees C, and near the point of outflow to almost ten million degrees.  It's this heating that caused it to produce gamma rays, which is how the structure was detected.

Not a phenomenon you'd want to be standing in the way of.

"We have traced the outflows of other galaxies, but we have never been able to actually map the motion of the gas," Bordoloi said, somehow resisting adding, and holy shit, this thing is amazing.  "The only reason we could do it here is because we are inside the Milky Way.  This vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow."

And, along the way, to figure out what's going on with the number one Weirdest Object in the Universe.  Having an explanation doesn't make it any less impressive, of course.  Gas at a temperature of ten million degrees being flung about at two million miles per hour by a ginormous black hole isn't exactly a cause for a shoulder-shrug.

Besides, there are forty-nine more weird objects (at least) left to explain.  If you're into science, it means you'll never be bored.

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The mind readers

In Isaac Asimov's deservedly famous short story "All the Troubles of the World," the megacomputer Multivac has so much data on each person in the world (including detailed brain scans) that it can predict ahead of time if someone is going to commit a crime.  This allows authorities to take appropriate measures -- defined, of course, in their own terms -- to prevent it from happening.

We took a step toward Asimov's dystopian vision, in which nothing you think is secret, with a paper this week in Nature Neuroscience about a new invention called a "brain activity decoder."

Developed by a team of researchers at the University of Texas at Austin, the software uses an fMRI machine to measure the neural activity in a person's brain, and is able to convert that neural activity into a continuous stream of text -- i.e., the output is what the person was thinking.

The researchers had volunteers listening to podcasts over headphones while the fMRI watched how their brains responded.  This allowed them to compare the actual text the test subjects were hearing with what the brain activity decoder picked up from them.  After only a short span of training the software, the results were scary good.  One listener heard, "I don't have my driver's license yet," and the decoder generated the output "She has not even started to learn to drive yet."  Another had the input, "I didn’t know whether to scream, cry or run away. Instead, I said, 'Leave me alone!'", which resulted in the output, "Started to scream and cry, and then she just said, 'I told you to leave me alone.'"

Not perfect, but as a proof-of-concept, it's jaw-dropping.

[Image licensed under the Creative Commons © Nevit Dilmen, Brain MRI 131058 rgbca, CC BY-SA 3.0]

The researchers touted its possible use for people who have lost the ability to communicate, in situations like locked-in syndrome.  However, I don't think it takes an overactive imagination to come up with ways such a device could be abused.  What would happen to the concept of privacy, if a machine could read your thoughts?  What about the Fifth Amendment right not to self-incriminate?  Like in Asimov's story, how could the authorities separate what a person had done from what they were contemplating doing?

Or would they?

Jerry Tang, who led the research, emphasizes that the decoder had to be trained on the person whose thoughts were going to be read; if it were trained on me, it couldn't immediately be used to figure out what you were thinking.  My response to that is: yet.  This is already leaps and bounds past previous attempts at thought-reading, which was only able to output single words and short sentences.  Given more time and further refinements, this technique will only get better.

Or scarier, as the case may be.

Tang also pointed out that even with improvements, the software would be defeated by someone putting up resistance (e.g., deliberately thinking other things to block the fMRI from getting the correct output).  He also is aware of the possibility of abuse.  "We take very seriously the concerns that it could be used for bad purposes and have worked to avoid that," he said.  "We want to make sure people only use these types of technologies when they want to and that it helps them."

Well, maybe.  I'm not a conspiracy-theory type, nor someone who thinks that all government is inherently bad.  Here, though, it seems like the potential for Orwellian thought-crime is a short step away.

Keep in mind, too, how generally inaccurate our brain's storage system is.  As we've seen over and over here at Skeptophilia, what we remember is an amalgam of what actually happened, what we were told happened, what we imagine happened, and a good dollop of falsehood.  False memories can be as convincingly real as accurate ones.  If the brain activity decoder were used on an unwilling person to extract his/her thoughts, there is no guarantee that the output would be at all reflective of reality.  In fact, it's almost certain not to be.

But since eyewitness testimony -- in other words, recall -- is considered one of the highest forms of evidence in a court of law, it's no stretch to wonder if a person's thoughts would be given the same undeserved weight.

I'm not sure what the right step is, honestly.  There are some who believe that a potential for misuse shouldn't stop scientific progress; anything, they argue, can be used for harm.  Others feel like the hazards can sometimes outweigh the benefits, and trusting the powers-that-be to do the right thing with technology this powerful is foolish.

I don't have an answer.  But I will say that my mind was forced back to the prescient quote from another seminal science fiction writer, Michael Crichton: "Scientists are preoccupied with accomplishment.  So they are focused on whether they can do something.  They never stop to ask if they should."

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Off the chart

Way back around 1910, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell independently found a curious pattern when they did a scatterplot correlation between stars' luminosities and temperatures.

The graph, now called the Hertzsprung-Russell Diagram in their honor, looks like this:

[Image licensed under the Creative Commons Richard Powell, HRDiagram, CC BY-SA 2.5]

Most stars fall on the bright swatch running from the hot, bright stars in the upper left to the cool, dim stars in the lower right; the overall trend for these stars is that the lower the temperature, the lower the luminosity.  Stars like this are called main-sequence stars.  (If you're curious, the letter designations along the top -- O, B, A, F, G, K, and M -- refer to the spectral class the star belongs to.  These classifications were the invention of the brilliant astronomer Antonia Maury, whose work in spectrography revolutionized our understanding of stellar evolution.)

There is also a sizable cluster of stars off to the upper right -- relatively low temperatures but very high luminosities.  These are giants and supergiants.  In the other corner are white dwarfs, the exposed cores of dead stars, with very high temperatures but low luminosity, which as they gradually cool slip downward to the left and finally go dark.

So there you have it; just about every star in the universe is either a main-sequence star, in the cluster with the giants and supergiants, or in the curved streak of dwarf stars at the bottom of the diagram.

Emphasis on the words "just about."

One star that challenges what we know about how stars evolve is the bizarre Stephenson 2-18, which is in the small, dim constellation Scutum ("the shield"), between Aquila and Sagittarius.  At an apparent magnitude of +15, it is only visible through a powerful telescope; it was only discovered in 1990 by American astronomer Charles Bruce Stephenson, after whom it is named.

Its appearance, a dim red point of light, hides how weird this thing actually is.

When Stephenson first analyzed it, he initially thought what he was coming up with couldn't possibly be correct.  For one thing, it is insanely bright, estimated at a hundred thousand times the Sun's luminosity.  Only its distance (19,000 light years) and some intervening dust clouds make it look dim.  Secondly, it's enormous.  No, really, you have no idea how big it is.  If you put Stephenson 2-18 where the Sun is, its outer edge would be somewhere near the orbit of Saturn.  You, right now, would be inside the star.  Ten billion Suns would fit inside Stephenson 2-18. 

If a photon of light circumnavigated the surface of the Sun, it would take a bit less than fifteen seconds.  To circle Stephenson 2-18 would take nine hours.

This puts Stephenson 2-18 almost off the Hertzsprung-Russell Diagram -- it's in the extreme upper right corner.  In fact, it's larger than what what stellar evolution says should be possible; the current model predicts the largest stars to have radii of no more than 1,500 times that of the Sun, and this behemoth is over 2,000 times larger.

Astronomers admit that this could have a simple explanation -- it's possible that the measurements of Stephenson 2-18 are overestimates.  But if not, there's something significant about stellar evolution we're not understanding.

Either way, this is one interesting object.

There's also a question about what Stephenson 2-18 will do next.  Astrophysicists suspect it might be about to blow off its outer layers and turn either into a luminous blue variable or a Wolf-Rayet star (the latter are so weird and violent I wrote about them here a while back).  So it may not be done astonishing us.

Puts me in mind of the quote from Richard Dawkins: "The feeling of awed wonder that science can give us is one of the highest experiences of which the human psyche is capable."

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The kludge factory

Know what a kludge is?

Coined by writer Jackson Granholm in 1962, a kludge is "an ill-assorted collection of poorly-matching parts, forming a distressing whole."  Usually created when a person is faced with fixing something and lacks (1) the correct parts, (2) the technical expertise to do it right, or (3) both, kludges fall into the "it works well enough for the time being" category.

[Image licensed under the Creative Commons Zoedovemany, Screen Shot 2015-11-19 at 11.54.48 AM, CC BY-SA 4.0]

Evolution is essentially a giant kludge factory.

At its heart, it's the "law of whatever works."  It's why the people who advocate Intelligent Design Creationism always give me a chuckle -- because if you know anything about biology, "intelligently designed" is the last thing a lot of it is.  Here are a few examples:

• Animals without hind legs -- notably whales and many snakes -- that have vestigial hind leg bones.
• Primates are some of the only mammals that cannot synthesize their own vitamin C -- yet we still carry the gene for making it.  It just doesn't work because it has a busted promoter.
• Human sinuses.  Yeah, you allergy sufferers know exactly what I'm saying.
• The recurrent laryngeal nerve in fish follows a fairly direct path, from the brain past the heart to the gills.  However, when fish evolved into land-dwelling forms and their anatomy changed -- their necks lengthening and their hearts moving lower into the body -- the recurrent laryngeal nerve got snagged on the circulatory system and had to lengthen as its path became more and more circuitous.  Now, in giraffes (for example), rather than going from the brain directly to the larynx, it goes right past its destination, loops under the heart, and then back up the neck to the larynx -- a distance of almost five meters.
• Our curved lower spines were clearly not "designed" to support a vertically-oriented body.  Have you ever seen a weight-bearing column with an s-bend?  No wonder so many of us develop lower back issues.
• One of the kludgiest of kludges is the male genitourinary tract.  Not only does the vas deferens loop way upward from the testicles (not quite as far as the giraffe's laryngeal nerve, admittedly), along the way it joins the urethra to form a single tube through the penis, something about which a friend of mine quipped, "There's intelligent design for you.  Routing a sewer pipe through a playground."  It also passes right through the prostate, a structure notorious for getting enlarged in older guys.  C'mon, God, you can do better than that.

The reason all this comes up is that the kludging goes all the way down to the molecular level.  A study from a team at Yale, Harvard, and MIT that appeared last week in the journal Science looked at the fact that when you compare the human genome to that of our nearest relatives, you find that one of the most significant differences is that our DNA has deleted sections.

That's right; some of why humans are human comes from genes that got knocked out in our ancestors.

The researchers found that there are about ten thousand bits of DNA, a lot of them consisting only of a couple of base pairs, that chimps and bonobos have and we don't.  A lot of these genetic losses were in regions involved in cognition, speech, and the development of the nervous system, all areas in which our differences are the most obvious.

The reason seems to have to do with gene switching.  Deleting a bit of switch that is intended to shut a gene off can leave the gene functioning for longer, with profound consequences.  Often these consequences are bad, of course.  There are some types of cancer (notably retinoblastoma) that are caused by a developmental gene having a faulty set of brakes.

But sometimes these changes in developmental patterns have a positive result, and therefore a selective advantage -- and we may owe our large brains and capacity for speech to kludgy switches.

"Often we think new biological functions must require new pieces of DNA, but this work shows us that deleting genetic code can result in profound consequences for traits make us unique as a species," said Steven Reilly, senior author of the paper.  "The deletion of this genetic information can have an effect that is the equivalent of removing three characters -- n't -- from the word isn't to create the new word is...  [Such deletions] can tweak the meaning of the instructions of how to make a human slightly, helping explain our bigger brains and complex cognition."

So yet another nail in the coffin of Intelligent Design Creationism, if you needed one.  Of course, I doubt it will convince anyone who wasn't already convinced; as I've observed more than once, you can't logic your way out of a belief you didn't logic your way into.

But at least it's good to know the science is unequivocal.  And, as astrophysicist Neil deGrasse Tyson said, "The wonderful thing about science is that it's true whether or not you believe in it."

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Pitch perfect

Consider the simple interrogative English sentence, "She gave the package to him today?"

Now, change one at a time which word is stressed:

• "She gave the package to him today?"
• "She gave the package to him today?"
• "She gave the package to him today?"
• "She gave the package to him today?"
• "She gave the package to him today?"

English isn't a tonal language -- where patterns of rise and fall of pitch change the meaning of a word -- but stress (usually as marked by pitch and loudness changes) sure can change the connotation of a sentence.  In the above example, the first one communicates incredulity that she was the one who delivered the package (the speaker expected someone else to do it), while the last one clearly indicates that the package should have been handed over some other time than today.

In tonal languages, like Mandarin, Thai, and Vietnamese, pitch shifts within words completely change the word's meaning.  In Mandarin, for example, mā (the vowel spoken with a high level tone) means "mother," while mă (the vowel spoken with a dip in tone in the middle, followed by a quick rise) means "horse."  While this may sound complex to people -- like myself -- who don't speak a tonal language, if you learn it as a child it simply becomes another marker of meaning, like the stress shifts I gave in my first example.  My guess is that if you're a native English speaker, if you heard any of the above sentences spoken aloud, you wouldn't even have to think about what subtext the speaker was trying to communicate.

What's interesting about all this is that because most of us learn spoken language when we're very little, which language(s) we're exposed to alters the wiring of the language-interpretive structures in our brain.  Exposed to distinctive differences early (like tonality shifts in Mandarin), and our brains adjust to handle those differences and interpret them easily.  It works the other way, too; the Japanese liquid consonant /ɾ/, such as the second consonant in the city name Hiroshima, is usually transcribed into English as an "r" but the sound it represents is often described as halfway between an English /r/ and and English /l/.  Technically, it's an apico-alveolar tap -- similar to the middle consonant in the most common American English pronunciation of bitter and butter.  The fascinating part is that monolingual Japanese children lose the sense of a distinction between /r/ and /l/, and when learning English as a second language, not only often have a hard time pronouncing them as different phonemes, they have a hard time hearing the difference when listening to native English speakers.

All of this is yet another example of the Sapir-Whorf hypothesis -- that the language(s) you speak alter your neurology, and therefore how you perceive the world -- something I've written about here before.

The reason all this comes up is a study in Current Biology this week showing that the language we speak modifies our musical ability -- and that speakers of tonal languages show an enhanced ability to remember melodies, but a decreased ability to mimic rhythms.  Makes sense, of course; if tone carries meaning in the language you speak, it's understandable your brain pays better attention to tonal shifts.

The rhythm thing, though, is interesting.  I've always had a natural rhythmic sense; my bandmate once quipped that if one of us played a wrong note, it was probably me, but if someone screwed up the rhythm, it was definitely her.  Among other styles, I play a lot of Balkan music, which is known for its oddball asymmetrical rhythms -- such wacky time signatures as 7/8, 11/16, 18/16, and (I kid you not) 25/16:

I picked up Balkan rhythms really quickly.  I have no idea where this ability came from.  I grew up in a relatively non-musical family -- neither of my parents played an instrument, and while we had records that were played occasionally, nobody in my extended family has anywhere near the passion for music that I do.  I have a near-photographic memory for melodies, and an innate sense of rhythm -- whatever its source.

In any case, the study is fascinating, and gives us some interesting clues about the link between language and music, and that the language we speak remodels our brain and changes how we hear and understand the music we listen to..  The two are deeply intertwined, there's no doubt about that; singing is a universal phenomenon.  And making music of other sorts goes back to our Neanderthal forebears, on the order of forty thousand years ago, to judge by the Divje Babe bone flute.

I wonder how this might be connected to what music we react emotionally to.  This is something I've wondered about for ages; why certain music (a good example for me is Stravinsky's Firebird) creates a powerful emotional reaction, and other pieces generate nothing more than a shoulder shrug.

Maybe I need to listen to Firebird and ponder the question further.

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Sounding off

Noodling around on Wikipedia, sometimes you run into the oddest stuff.

I was looking something up yesterday and saw an associated link to a page called "List of Unexplained Sounds."  Well, I couldn't pass by something like that, so off I went down that rabbit hole.  As advertised, the page is a compendium of odd noises that have been heard (many have been recorded, so we know that those at least aren't someone's overactive imagination).  There are sound clips for a few of them, so I highly recommend going to the page and checking them out.

Here are a few of the ones listed -- with some possible explanations.

Upsweep is the name given to a sound consisting of a repeated series of rising tones that sound to my ears a little like a siren.  The source of the sound has been identified as being somewhere near 54° S latitude, 140° W longitude, placing it a little less than halfway from New Zealand and Cape Horn.  This, to put it mildly, is the middle of abso-fucking-lutely nowhere; in fact, it's not far from Point Nemo, also known as the "oceanic pole of maximum inaccessibility," which at 48°52.6′S 123°23.6′W is the point on Earth that is maximally distant from land.  There's a conjecture that Upsweep might be some kind of sound generated by underwater volcanic activity, but it's not exactly convenient to go out there and check, so that hypothesis is unproven.

The Bloop is a famous noise, once again heard in the Pacific Ocean, that is ultra-low frequency and extremely high amplitude -- meaning it can travel thousands of miles from its source.  The guess here is that the Bloop is a sound made by large icebergs breaking up (or scraping the seafloor), but I've heard an alternate hypothesis that I like better, which is that it's Cthulhu snoring.  Cthulhu, as you probably know, is the octopoid Elder God who was put into a charmèd sleep in his underwater city of Rl'yeh, where he's waiting for his followers to summon him back.  Why anyone would want to do so remains to be seen, because if you've read any H. P. Lovecraft, you know that the ones who try to reawaken him always end up dying in nasty ways, so it seems to me it might be better to leave him blooping peacefully in Rl'yeh.

[Image licensed under the Creative Commons Dominique Signoret (signodom.club.fr), Cthulhu and R'lyeh, CC BY-SA 3.0]

Some sounds have only been heard once, but are weird enough to bear mention.  These include Julia, which was given its name because it sounds like someone saying the name in a weird, hooting voice.  This is another one that is probably due to icebergs; its origin was pinpointed to somewhere near Cape Adare, Antarctica, but it was loud enough to be recorded by the entire Equatorial Pacific Autonomous Hydrophone Array.

The Ping is much more local; it's only been reported from the Fury and Hecla Strait between Baffin Island and the Melville Peninsula, Nunavut, Canada.  Although it's likely to be from some kind of marine animal, it's strange enough (and has been reported enough times) that "the Canadian military is investigating."

Not all of them are oceanic sounds.  One of the weirdest is the Forest Grove Sound, heard multiple times near Forest Grove, Oregon in February of 2016.  It was variously described as "a mechanical scream," "a giant flute played off pitch," and "akin to a bad one-note violin solo broadcast over a microphone with nonstop feedback."  There was an investigation, and it was never satisfactorily resolved -- and has not been heard since.

Last, there are the Moodus Noises, heard near Moodus, Connecticut, which unlike the Forest Grove Sound, have been heard for centuries (the indigenous people of the area, mostly from the Narragansett Tribe, supposedly have a long tradition of weird noises coming from nearby Cave Hill and Mt. Tom).  The Moodus Noises have a different Lovecraftian connection -- apparently they were the inspiration for the strange noises that came from Sentinel Hill in the spine-chilling story "The Dunwich Horror."  The more prosaic explanation for the Moodus Noises is that they come from microquakes, but -- needless to say -- there are a lot of people who don't buy that, and think the region is haunted.

So there you have it; a sampler of weird and unexplained sounds.  You should definitely check out the page and listen to some of the clips, which are goosebump-inducing.  While I do think they all have perfectly ordinary natural explanations, being a diehard skeptic doesn't mean I'm immune from getting the creeps now and again.

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Fingerprint of a megaflood

The Camarinal Sill is a curious geological feature that lies twenty kilometers to the east of the narrowest point of the Straits of Gibraltar.  It's an underwater rise that at its top is three hundred meters from the surface, with (much) deeper water on either side.

So the tips of the pincers forming the Straits also has a third pincer coming from below.  And to make things ever more interesting, the northern and southern points are on separate tectonic plates -- the Eurasian Plate to the north, the African Plate to the south.  These two plates have different relative motions, which is why around six million years ago, the straits abruptly closed up, and for a time, there was dry land between what are now Spain and Morocco.

The problem is, the region around the Mediterranean Sea is hot and dry (and was back then, too).  With the Atlantic Ocean now cut off, the only inflows of water into the Mediterranean came from all the rivers draining into it.  But the sum total of all that water entering it was still exceeded by the evaporation rate from the parched air passing over it.

So the Mediterranean Sea began to dry up.

Over the next six hundred thousand years, the sea level dropped by several kilometers, leaving behind a desiccated desert and a few widely separated lakes of concentrated brine.  The temperatures in the region rose by an estimated 15 C year-round, creating a climate more like the central Sahara than the pleasant "Mediterranean climate" that places like Italy, Greece, Spain, and southern France now enjoy.  The minerals from the evaporated sea water were left behind, creating layers of salt, gypsum, aragonite, and calcite that can still be seen today. 

Map of western Europe and northern Africa during the "Messinian Salinity Crisis;" the inset is an artist's depiction of the terrain [Image licensed under the Creative Commons Paubahi, Inserciomamifers, CC BY-SA 3.0]

Then, 5.33 million years ago, there was another tectonic shift, and the two sides of the Camarinal Sill pulled apart.

At that point there was a five-kilometer difference in the sea level between the Atlantic and what was left of the Mediterranean Sea; in fact, from the shore of the Atlantic west of Gibraltar to the nearest Mediterranean brine lake was a distance of over three hundred kilometers.

The result was a flood to end all floods.

The "Zanclean Deluge" was so enormous it's hard to visualize.  The waterfall over the newly-created Straits of Gibraltar was so powerful it eroded a nine-hundred-meter-deep gorge in the seabed.  The water level rose by an estimated ten meters a day for a year, ultimately refilling the entire Mediterranean Basin.  

[Nota bene: before any biblical literalists @ me with comments like "Ha-ha, that proves the Great Flood in the Book of Genesis actually happened!", allow me to point out that (1) the Zanclean Deluge had nothing to do with forty days and nights of rain, and (2) 5.33 million years ago our ancestors were small-brained hominins called Ardipithecus that lived in what is now Ethiopia, Tanzania, and Kenya.  There is, I might add, no evidence that Ardipithecus could build giant boats, nor were they capable of going to Australia to fetch a pair of kangaroos so they could be saved from the Flood and bringing them back after God finished smiting the absolute shit out of everyone and the waters receded.  Oh, and (3), don't you people disbelieve in plate tectonics anyhow?] 

Anyhow, the reason this all comes up is that a team of geologists from Utrecht University, the Royal Holloway University in London, and the University of Granada have just found the first unequivocal direct evidence that all this happened -- a deposit of gypsum, sandstone, and marl (lime-rich silt) showing distinct ripple marks from flowing water.  Upon analysis, they showed that the water was traveling really fast (something that can be determined from the wavelength of the ripple marks and the size distribution of the particles), was moving from west to east, and -- the clincher -- the entire formation dated to right around 5.33 million years ago.

Smoking gun, that.

"Now, for the first time, we can directly prove and quantify one of the most catastrophic periods of environmental change on our planet, which until now we had only been able to describe in geophysical models," said Gils Van Dijk, who led the study.  "Moreover, geologists are trained to use contemporary processes on the Earth’s surface to interpret what we observe in rocks.  But here we can’t rely on that knowledge, because we don’t know of any similar phenomena from at least the past one hundred million years."

What's a little sobering is that the tectonic movement that caused the whole thing -- both the closing of the sill and the reopening and subsequent flood -- is still happening.  The African Plate is still inching northward with respect to the Eurasian Plate, so the pattern is going to repeat.  Eventually, Gibraltar will seal up permanently, and the Mediterranean Sea will disappear -- and the coastal regions' pleasant climate will once again become a furnace, like it was 5.5-odd million years ago.

It won't happen within our lifetimes, of course; we're talking geological time scales, here.  But it always bears keeping in mind that the permanence of our landscapes and climates is an illusion, caused by our vision being limited to our short life spans.  On the larger scales, Tennyson was closer to the mark, in his beautiful poem "In Memoriam":

There rolls the wave where grew the tree.

O Earth, what changes hast thou seen?

There where the long road roars has been

The stillness of the central sea.

The hills are shadows, and they flow

From form to form, and nothing stands,

They melt like mists, the solid lands --

Like clouds, they shape themselves, and go.

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