Celestial whack-a-mole

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

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

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

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

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

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

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

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

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

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

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

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

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

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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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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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Springtime collision

I've written here before about the rather sobering topic of mass extinctions, and from what reading I've done on the topic, it always leaves me thinking about how fragile Earth's ecosystems are.  Most of the biggest extinctions were not due to a single cause, though; for example, the Ordovician-Silurian extinction of about 445 million years ago seems to have been touched off by plate tectonics -- the massive southern continent of Gondwana meandered across the south pole, leading to ice cap formation, massive glaciation, and a drop in sea level.  However, there followed a huge drop in atmospheric oxygen and spike in sulfur, leading to worldwide oceanic anoxia.  The result: an estimate 60% mortality rate in species all over the Earth.

Anoxia is also thought to have played a role in the largest mass extinction ever, the Permian-Triassic extinction of 252 million years ago.  This one, however, seems to have begun with a catastrophic volcanic eruption that boosted the carbon dioxide in the atmosphere, and thus the temperature.  Temperature is inversely related to oxygen solubility, so as the oceans warmed, what oxygen was left in the air didn't dissolve as well, and nearly everything in the oceans died (a mortality rate estimated at an almost unimaginable 95%).  This caused an explosive growth in anaerobic bacteria, pumping both carbon dioxide and methane into the atmosphere.  The average temperature skyrocketed by as much as ten degrees Celsius.

Even the smaller extinctions seldom come from one cause.  I wrote recently about the Eocene-Oligocene extinction, which wiped out a good many of Africa's mammal species (our ancestors survived, fortunately for us), and was apparently an evil confluence of three unrelated events -- rapid cooling of the climate after the Paleocene-Eocene Thermal Maximum, a massive meteorite collision near what is now Chesapeake Bay, and explosive volcanism in Ethiopia.

The exception to the rule seems to be the most famous extinction of all, the Cretaceous-Tertiary extinction of 66 million years ago.  The one that ended the hegemony of the dinosaurs.  I always find it wryly amusing when the dinosaurs are described as some kind of evolutionary dead-end, as if their failure to survive to today is indicative that they were inferior or maladapted.  In fact, the dinosaurs as such were the dominant group of terrestrial animals for almost two hundred million years -- from the late Permian to the end of the Cretaceous -- and that's not counting birds, which are (frankly) dinosaurs, too.  That means if you consider the earliest modern humans to have lived in Africa on the order of three hundred thousand years ago, the dinosaurs kind of ran the planet for over six hundred times longer than we've even existed.

And in the blink of an eye, everything changed.  Far from being an evolutionary cul-de-sac, the dinosaurs were doing just fine, when a meteor ten kilometers in diameter slammed into the Earth near what is now the Yucatán Peninsula of Mexico.  And now scientists have been able to pinpoint not only where the collision happened, but what time of year -- the middle of the Northern Hemisphere's spring.

The Chicxulub Impact, as visualized by artist Donald E. Davis [image is in the Public Domain courtesy of NASA]

Paleontologists working in North Dakota have found a rich fossil site that was created on that fateful day.  Pre-collision, the area was a wet lowland forest with a shallow river.  The slow-moving water was the home of paddlefish and sturgeon, swimming slowly and nosing around in the mud for food.  Then, three thousand kilometers away, the meteor struck.  The shock wave ejected a sheet of superheated steam and molten rock skyward; the impact, which occurred in what was (and still is) a shallow marine region, generated a tsunami the likes of which I can't even imagine.  The southern part of North America got flash-fried by the heat generated by the strike; only a few minutes later, it was followed by a wall of water the height of a skyscraper that swept across the land at an estimated five hundred kilometers an hour.

The first thing the fish would have noticed, though, is a rain of tiny globs of molten glass that sizzled as they hit the water and settled out, coating the riverbed and clogging their gills.  Then the tsunami hit, burying the site under thick layers of sediment.  By the time things calmed down, most of the living things in North America were dead, their fossils left behind as a near-instantaneous photograph of one of the worst days the Earth has ever seen.

It's the quickness of the event that allowed scientists to figure out when it happened.  Paddlefish bones form growth layers -- a little like the rings inside a tree trunk -- and all of the paddlefish fossils from the site show an increasing rate of growth, but not yet at its annual peak (which occurs in the warmest parts of summer).  The Chicxulub meteorite seems to have struck the Earth in April or May.

This may be another reason why the Northern Hemisphere flora and fauna took a much bigger hit than the ones in the Southern Hemisphere.  The initial explanation was that the meteor struck the Earth at an angle, on with a trajectory on the order of forty-five degrees south of vertical, so the shower of molten debris mostly got blasted northward.  (This may well be true; the current research doesn't contradict that assessment.)  But if the strike occurred in the Northern Hemisphere's spring, when plants are leafing out and flowering, and animals increasing in activity, it would have been catastrophic.  The ones in the Southern Hemisphere, heading into fall and winter, would have been in the process of powering down and moving toward dormancy and hibernation, and may have been more insulated from the effects.

Besides the obvious fascination of an event so cataclysmic, it's just stupendous that we can analyze the evidence so finely that we can determine what time of year it occurred, 66 million years later.  It also highlights how suddenly things can change.  The dinosaurs had been around for two hundred million years, surviving not only the colossal Permian-Triassic extinction but the smaller (but still huge) end-Triassic extinction, that took out thirty percent of the species on Earth.  In one particular April of 66 million years ago, a quick look around would have led you to believe that everything was fine, and that the dinosaurs and other Mesozoic critters weren't going anywhere.

A day later, the entire face of the Earth had changed forever.

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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!]

Life finds a way

I've dealt more than once here at Skeptophilia with the repeated mass extinctions the Earth has undergone.  Part of this is that I have an admitted fascination with things that are big and powerful and can kill you.  These include:

• tornadoes and hurricanes
• lightning
• earthquakes
• volcanoes
• death asteroids from outer space

The latter is thought to have been the prime mover of the Cretaceous Extinction, which occurred 66 million years ago and killed an estimated 75% of the species on Earth, including all of the large dinosaurs (the exception being the lineage that led to modern birds).  Here's a cool, if terrifying, simulation of what it'd be like if the Earth got hit by an asteroid five hundred kilometers in diameter (the Chicxulub Meteorite, which caused the extinction, is estimated to be about a tenth that diameter, so you can scale down your picture of that event accordingly):

But dwelling on that stuff is a little morbid, even if it's kind of awe-inspiring.  So today, I'd like to look at some recent research that looks at how life recovered after the cataclysm -- discoveries that suggest the encouraging idea that even with a catastrophe, life can bounce back amazingly quickly.

A few years ago, Ian Miller and Tyler Lyson of the Denver Museum of Nature and Science were involved in a fossil dig in Corral Bluffs, Colorado, and made a rather astonishing discovery.  Initially the area seemed to be rather fossil-poor, but it had a great many concretions (roughly spherical blobs of cemented sediment).  When Miller and Lyson split one of these open, they found it was full of skeletal remains.

It turns out Corral Bluffs represent sedimentary layers of rock deposited immediately after the collision, so it provides an incredibly detailed record of the years following.  Large animals and flowering plants (especially trees) were hit the hardest by the extinction; despite the prevailing wisdom that "dinosaurs died and mammals didn't," the more accurate statement is "big species were much more likely to die than little ones."  The bottleneck, in fact, seems to have taken out all the mammals larger than your average rat.  (Miller and Lyson found no evidence of mammals larger than six hundred grams that survived the extinction.)  Miller, who is a paleobotanist, concentrated not on the animal remains but the plants -- especially the 37,000 pollen grains he found fossilized in the sediment layers.  And from this, a picture began to emerge of what things were like in the years following the collision, which was described this week in a fascinating paper in Science.

The largest group of plants to come through the bottleneck were ferns, which thrive in disturbed areas and have spores that are pretty damage-resistant.  Unfortunately for the animals, fern leaves and roots are rather low in nutrients, so for a while, body sizes remained small because there simply wasn't enough food around to support big, or even medium-sized, herbivores.  But within a few thousand years -- a flash, evolutionarily speaking -- Fern World was replaced by Palm World, as proto-monocots (the group that contains not only palms, but grasses, lilies, orchids, irises, and a variety of other familiar plant families) evolved to be more robust.  Palms have oily fruit that are high in sugar, and there's a commensurate jump in mammalian body size, with species showing up that weighed five kilograms.

Palms were superseded by the ancestors of today's walnuts and hickories a hundred or so thousand years after that, and in "Pecan Pie World" (as Miller and Lyson call this era), and the higher nutritional quality of those seeds fueled another jump in body size, with the largest ones reaching thirty kilograms (the size of a large dog).  And after seven hundred thousand years, legumes diversified, and the high protein content of these species triggered another growth spurt, topping out at fifty kilograms -- a hundred times larger than the survivors of the collision, in less than a million years.

Nota bene: the growth in size wasn't done yet.  The Oligocene Epoch, from 34 to 23 million years ago, saw the largest land mammals that have ever existed, including the enormous Baluchitherium, a behemoth that could have converted an African elephant into an African elephant pancake:

[Image licensed under the Creative Commons Waqas-anees2014, Baluchitherium, The Largest Land mammal at Pakistan Museum of Natural History (PMNH), CC BY-SA 3.0]

The Miller and Lyson study offers us a message that is simultaneously reassuring and terrifying.  First, the human-caused "Sixth Extinction" that we are almost certainly undergoing as we speak is not going to eliminate life on Earth, and the species that survive will quickly spring back and diversify once we stop doing whatever we can to make the planet uninhabitable.  But the cautionary tale is that no matter what, it won't be what we had.  The diversity of flora and fauna that existed before the Chicxulub Collision was gone forever, and even though "life found a way" (to borrow a phrase from Jurassic Park), what evolved afterward was dramatically different than what was lost.  And, to put not too fine a point on it, the years immediately following the bottleneck were pretty freakin' horrible for all concerned, with an entire planet laid waste, and the animals that weren't directly killed by the impact itself largely facing habitat loss and rampant starvation.

So we shouldn't be so quick to adopt the Pollyanna-ish "it'll all be fine, nature is resilient" attitude toward our current fossil-fuel-crazy, pollution-blind willfully ignorant behavior.  If anything, we should recognize how fragile it all is -- and how, if we push too hard, we're likely to see a collapse of catastrophic proportions.  While we can pretty much count on evolution eventually producing a whole new set of what Darwin called "endless forms most beautiful and most wonderful," there's more than a passing chance that we won't be around to see them.

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In keeping with Monday's post, this week's Skeptophilia book recommendation is about one of the most enigmatic figures in mathematics; the Indian prodigy Srinivasa Ramanujan.  Ramanujan was remarkable not only for his adeptness in handling numbers, but for his insight; one of his most famous moments was the discovery of "taxicab numbers" (I'll leave you to read the book to find out why they're called that), which are numbers that are expressible as the sum of two cubes, two different ways.

For example, 1,729 is the sum of 1 cubed and 12 cubed; it's also the sum of 9 cubed and 10 cubed.

What's fascinating about Ramanujan is that when he discovered this, it just leapt out at him.  He looked at 1,729 and immediately recognized that it had this odd property.  When he shared it with a friend, he was kind of amazed that the friend didn't jump to the same realization.

"How did you know that?" the friend asked.

Ramanujan shrugged.  "It was obvious."

The Man Who Knew Infinity by Robert Kanigel is the story of Ramanujan, whose life ended from tuberculosis at the young age of 32.  It's a brilliant, intriguing, and deeply perplexing book, looking at the mind of a savant -- someone who is so much better than most of us at a particular subject that it's hard even to conceive.  But Kanigel doesn't just hold up Ramanujan as some kind of odd specimen; he looks at the human side of a man whose phenomenal abilities put him in a class by himself.

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