Footprints in the boneyard

The difficulty with paleontology is its inherent limitations.

There are, of course, things it's very good at.  In the hands of a skilled expert, fossils can tell you a great deal -- not only direct information about the parts that are preserved, but indirect information (from spaces, gaps, muscle attachment points, and so on) about the parts that were not.  I'm currently reading the wonderful book by Jack Horner and Edwin Dobb, Dinosaur Lives: Unearthing an Evolutionary Saga, and was astonished to find out that many paleontologists now believe that the quintessential Big Scary Dinosaur, Tyrannosaurus rex, was primarily a scavenger and not a hunter -- based upon the fact that the interior of the skull shows that its brain had an enormous olfactory lobe and a correspondingly small visual cortex, similar to hyenas and vultures.

Even so, there's a lot that fossils have a harder time telling us.  Other than a few fortuitous exceptionally-preserved feathers, we know next to nothing about colors and markings; art featuring prehistoric animals is almost entirely basing those features on guesswork using the patterns we see in modern animals.  In addition, how ancient organisms fit into the bigger ecological picture is like trying to figure out the pattern in a thousand-piece puzzle when you only have a handful of pieces. Given that a very small percentage of the biological remains left behind ever become fossils, chances are there are tens of thousands of prehistoric species we know absolutely nothing about because they left no traces behind after the last of their kind died.

Behavior, too, is often a puzzle.  It was Jack Horner (the same Jack Horner who co-wrote Dinosaur Lives) who made the discovery of the nesting and parental care behavior in the duckbilled dinosaur Maiasaura (the name means "good mother lizard"), based upon a group of fifteen fossilized juveniles and one adult that had been killed simultaneously in a volcanic ashfall.  But despite what Jurassic Park would have you believe, we really know very little about the behavior of prehistoric animals.  (Dilophosaurus, for example, almost certainly didn't have a retractable frill and poisonous spit.  Spit rarely fossilizes.)

The reason the topic comes up, actually, is because of a different volcanic eruption that left behind a treasure trove of fossils; a "supereruption" of the Yellowstone volcanic system twelve million years ago that smothered (and preserved) a huge herd of the prehistoric North American rhinoceros species Teleoceras.  The site -- in what is now northeastern Nebraska -- has been nicknamed "the rhino Pompeii."

"The eruption was so massive that ash would have fallen like snow 1,600 kilometers from the eruption site in Idaho," said Ashley Poust, a curator of vertebrate paleontology at the University of Nebraska State Museum, who gave a talk on the find last week at the annual meeting of the Society for Vertebrate Paleontology.  "This would have darkened the skies, buried plant life and water sources, and been a real hazard to anything with a delicate respiratory system."

A paleontologist working on unearthing Teleoceras fossils in the Ashfall Fossil Beds [Image credit: Ashley Poust]

What's most amazing about this find, though, is that the study also uncovered footprints in the ash -- the traces of two species of "bone-crushing dogs," Aelurodon taxoides and Epicyon saevus, which apparently somehow escaped being suffocated themselves and afterward made use of the huge amounts of free meat from the dead rhinos.  Aelurodon and Epicyon seem to have occupied the same niche as modern hyenas, but were a lot bigger; these prints were about eight centimeters long and seven centimeters wide.

Reconstruction of Epicyon [Image licensed under the Creative Commons Jarrod Amoore from Sydney, Australia, Epicyon, CC BY 2.0]

"There is some evidence that they may have scavenged among the animals who didn't survive, using the buried rhinos as a food cache," Poust said.  "But since we haven't found the bones of these meat eaters, we aren't sure yet whether this was enough to see them through to better times, or whether they eventually had to depart to seek their fortunes elsewhere in the massive disaster zone that covered much of North America."

It's also uncertain how they survived.  Volcanic ash is nasty stuff.  Not only does it clog airways if inhaled, it's made of sharp slivers of something very much like glass.  Even walking through a recent ashfall would raise enough dust to cause significant health risk, much less living through it while it was actively falling out of the sky.  Interesting that there haven't been any fossils of the dogs found at the site -- although research is ongoing, and it's anyone's guess about what's left there to discover.

So here's another case where we can made at least some tentative inferences about behavior from twelve million year old fossils.  Although the sad truth is that we still have access to information about only a tiny percent of the life that has ever existed on Earth, sometimes a chance discovery will give us a startling window into the past -- in this case about packs of scavengers that may have taken advantage of a catastrophic disaster.

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Resurrection

The environmentalists tell us "extinction is forever," and that certainly seems unarguable.  Once a species is lost, evolution will never recreate it.  You may get something that looks like it; there are numerous examples of Elvis taxa, species that evolved to fit vacated niches and underwent convergent evolution resulting in a similarity to some extinct form.  (The name comes from the huge numbers of Elvis impersonators that have popped up since the original's death in 1977.)  But the sad truth is that the original is gone forever.

The issue, though, can be making certain the species actually is extinct.  There are ongoing efforts to find relic populations of a number of presumed-extinct species (two of the best known are the ivory-billed woodpecker and the thylacine).  Naysayers have criticized the efforts to find these species as nothing more than wishful thinking, but it bears keeping in mind that there is a long list of organisms thought to be extinct that have turned out to be very much alive.

They're called Lazarus taxa, after the biblical character Jesus raised from the dead.  Some of them are astonishing.  The one that always comes to mind for most people is the coelacanth, a crossopterygian fish that was only known from fossils preceding the Cretaceous Extinction sixty-six million years ago, which was discovered living in the Indian Ocean in 1938.  But that's only one of many.  Here's a sampler of Lazarus taxa:

• The South American bush dog (now split into three separate species in the genus Speothos) was only known from some Pleistocene-age bones found in a Brazilian cave, but is now known to have a range from southern Central America all the way to northern Paraguay.  Its reclusive habits and rarity still make it the least-studied canid in the world.

A Brazilian bush dog [Image licensed under the Creative Commons Xerini, Waldhund, CC BY-SA 3.0]

• The nightcap oak (Eidothea hardeniana and E. zoexylocarya), which aren't oaks at all but a member of the Protea family (Proteaceae), were known only from fifteen-million-year-old fossils -- and then a stand of them were discovered growing in a remote part of Australia.  The Royal Botanical Gardens in Sydney has a cultivation program for the two species, which are threatened because the seeds are frequently eaten by introduced mice.

Eidothea hardeniana [Image is in the Public Domain]

• The monito del monte, or colocolo opossum (Dromiciops gliroides), was not only thought to have gone extinct eleven million years ago, it was believed that its entire order (Microbiotheria) was gone as well.  It was found -- alive -- in the temperate bamboo forests of the southern Andes Mountains in 1894, and has no near relatives anywhere in the world.  (The closest are the Australian marsupials, but even those are very distant cousins.)

[Image licensed under the Creative Commons José Luis Bartheld from Valdivia, Chile, Monito del Monte ps6, CC BY 2.0]

• In 1898 a fish was discovered that was a near perfect match to Oligocene-age fossils on the order of twenty-eight million years old.  It's Lignobrycon myersi, and is only known from the Rio Braço and Rio Contas in east-central Brazil.  Somehow, it alone of its genus survived through all of those years and made it down to the present day.

[Image licensed under the Creative Commons Alexandre dos Santos Rodrigues et. al., Lignobrycon myersi specimens (9382613) (cropped), CC BY 4.0]

• The monoplacophorans were a group of mollusks common during the Silurian and Devonian Periods, but were last seen in the fossil record in the mid- to late-Devonian, around 375 million years ago.  After that -- nothing.  Reasonably, biologists thought they'd gone extinct, until live monoplacophorans were discovered in deep water off the west coast of Costa Rica.  Further surveys have found no fewer than thirty-seven different species in deep water across the Pacific.

A live specimen of Neopilina filmed off the coast of Samoa by the 2017 Okeanos Explorer mission [Image is in the Public Domain courtesy of NOAA]

• Even the monoplacophorans don't hold the survival record, though.  That honor goes to Rhabdopleura, which is a graptolite -- a (very) distant relative of chordates known mainly through Cambrian-age fossils.  The last Rhabodopleura was thought to have gone extinct in the mid-Cambrian, five hundred million years ago (and the rest of the group didn't make it past the mid-Carboniferous).  In 1869 they were discovered living in the deep water of the Pacific, and since that time nine living species have been identified.

A drawing of Rhabdopleura normani [Image is in the Public Domain]

While the general rule still applies -- extinction is forever -- it's worth keeping in mind that sometimes we find ourselves in a situation a little like Mark Twain did, resulting in his quip, "Rumors of my death were great exaggerations."  The Earth is a big place, and there are still plenty of poorly-explored regions where we might well have lots of surprises in store.

All of which should be encouraging to the folks out there chasing the ivory-billed woodpecker and thylacine.  Don't give up hope.  If Rhabdopleura could survive for five hundred million years unobserved, surely these two could manage a century or so.

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The ghost forests

I recently read paleontologist Riley Black's lovely book When the Earth Was Green: Plants, Animals, and Evolution's Greatest Romance, which looks at the prehistory of life on Earth through the lens of paleobotany.

While I know the charismatic megafauna like dinosaurs and saber-toothed tigers and giant ground sloths garner most of the attention, I've always found ancient plants equally interesting.  Part of that comes from my ongoing love of both gardening and wild plants, something I've experienced since I was about six and discovered F. Schuyler Mathews's Field Book of American Trees and Shrubs, with its hundreds of pages of descriptions and range maps and wonderful illustrations.  I can't even begin to estimate the amount of time I spent poring over its pages (and I still own my copy of it).

Once I gained a passing knowledge of the trees and shrubs and wildflowers I saw every day, I was shocked to find out that if I were to go back a few million years, I'd find an entirely different assemblage of plant species.  I know, it shouldn't have been a surprise; if the animals had changed, there's no reason the plants wouldn't have as well.  But I still found it astonishing when I found out that (for example) at the moment, there is exactly one extant species of ginkgo (the familiar, and beautiful, Ginkgo biloba), but in the past there had been hundreds, perhaps thousands, of species in the family:

A sampler of now-extinct Jurassic ginkgo species [Image licensed under the Creative Commons Peter R. Crane, Pollyanna von Knorring, Fossil Ginkgoales, CC BY 4.0]

Riley Black does a masterful job of tracing the evolutionary history of plants from their origins to recent times, and her signature lucid writing style makes the subject completely captivating.  One of the chapters deals with an odd period of Earth's history -- the Cretaceous Resinous Interval, a span of about fifty million years during which there was intense diversification amongst gymnosperms, a group that includes not only ginkgos, but the superficially palm-like cycads and the much more familiar conifers.

Anyone who has ever leaned up against a pine or spruce tree knows about their impossibly sticky, golden-brown, aromatic sap.  This glop, so unfortunate for skin and clothing, evolved as a way of sealing wounds and preventing insect damage.  So in a relatively short time, we see the evolution of hundreds of species of plants that produced the stuff -- and, when it met the right conditions, hardening into amber.

Most of the world's amber, whether from Burma or the Baltic region or the highlands of Ecuador and Peru, formed during this time.  Amber has been popular for jewelry-making since the time of the ancient Greeks, and probably before; in fact, an interesting linguistic side-note is that the Greek name for amber, ἤλεκτρον, is where our words electron and electricity come from (due to amber's property of gaining a static charge when rubbed with a silk cloth).  But amber really came into the popular consciousness because of Jurassic Park, wherein some scientists extract dinosaur blood from bloodsucking insects trapped in amber, and use it to clone dinosaurs, with predictable results.

[Nota bene: it's thought that the upper bound for the survival of DNA in amber, even with optimal conditions, is around a million years, not the hundreds of millions required by Jurassic Park.  And even that is likely to be an overestimate.  In 2013, scientists tried -- and failed -- to extract intact DNA from a bee trapped in ten thousand year old copal, an amber precursor.]

That doesn't mean it can't have phenomenal paleontological significance, however, even if we're unlikely to have velociraptors stalking us any time soon.  The reason the topic comes up is a paper that appeared last week in Communications Earth about 112-million-year-old amber unearthed in an Ecuadorean quarry, which contained so many inclusions of insects, pollen, and seeds that it's being called a "Cretaceous time capsule."

A midge from the Ecuadorean amber.  Check out how well preserved those compound eyes and antennae are!  [Image credit: Mónica Solórzano-Kraemer]

The number of insect and arachnid taxa represented, as well as the pollen and other plant fossils discovered, paint a remarkably detailed picture of the ecosystem back then.  The authors write:

The new palaeobotanical evidence suggests the presence of a diverse and humid, low-latitude forest in north-western Gondwana during the early Albian...  The strata in this quarry reveal a vertical evolution of various palaeoenvironments, including proximal braided rivers, lacustrine systems, hyperpycnal [high-density, high-sediment] flows, and distal braided rivers during the Albian...  Pollen and plant macrofossils show abundant ferns and fern-allies that likely grew in the understory and/or near water bodies, in a forest dominated by araucariacean resinous trees.  The overall palynological and plant macrofossil association found in the Genoveva quarry, particularly the high diversity of pteridophytes and the presence of moderately thick coal seams in the stratigraphic sequence, indicates a humid environment, similar to previous reports in other but less studied north-western tropical South American sites.

The presence of relatively abundant chironomid flies and one trichopteran as bioinclusions—both insect groups with aquatic larval stages—further supports the interpretation of predominantly humid conditions during resin production and deposition.

Fascinating to think that if you went back there, in that thriving humid lowland forest, you wouldn't see a single modern plant species.  Not one.  Groups, sure -- we still have araucariacean trees around today (the most familiar being the Norfolk Island pine and the monkey-puzzle tree) -- but our modern forests, even in habitats with similar climates, have no species in common with those that produced the 112-million-year-old Genoveva amber. 

Change is always the way of things, but still, it strikes me as sad that all those many forms most beautiful and most wonderful (to swipe Darwin's pithy phrase) are gone.  Last week at the Tompkins County Friends of the Library Used Book Sale -- a twice-a-year, three week long, must-attend event for any bibliophiles within driving distance of Ithaca, New York, and which offers a quarter of a million used books each go round -- I picked up a real prize in a lovely illustrated paleobotany text, with drawings and fossil photographs representing over a thousand different species of plants no longer to be found anywhere on Earth.

I think this morning I'll spend some time flipping through its pages, and dream of wandering through the ghostly forests of prehistory.

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The skull in the cave

"If humans came from monkeys, why are there still monkeys?"

If there is one phrase that makes me want to throw a chair across the room, it's that one.  (Oh, that and, "The Big Bang means that nothing exploded and became everything.")  Despite the fact that a quick read of any of a number of reputable sites about evolution would make it clear that the question is ridiculous, I still see it asked in such a way that the person evidently thinks they've scored some serious points in the debate.  My usual response is, "My ancestors came from France.  Why are there still French people?"  But the equivalence of the two seems to go so far over their heads that it doesn't even ruffle their hair.

Of course, not all the blame lies with the creationists and their ilk.  How many times have you seen, in otherwise accurate sources, human evolution depicted with an illustration like this?

It sure as hell looks like each successive form completely replaced the one before it, so laypeople are perhaps to be excused for coming away with the impression that this is always the way evolution works.  In fact, cladogenesis (branching evolution) is far and away the more common pattern, where species split over and over again, with different branches evolving at different rates or in different directions, and some of them becoming extinct.

If you're curious, this is the current best model we have for the evolution of hominins:

The cladogenesis of the hominin lineage; the vertical axis is time in millions of years before present  [Image licensed under the Creative Commons Dbachmann, Hominini lineage, CC BY-SA 4.0]

The problem also lies with the word species, which is far and away the mushiest definition in all of biological science.  As my evolutionary biology professor put it, "The only reason we came up with the idea of species as being these little impermeable containers is that we have no near relatives."  In fact, we now know that many morphologically distinct populations, such as the Neanderthals and Denisovans, freely interbred with "modern" Homo sapiens.  Most people of European descent have Neanderthal markers in their DNA; when I had my DNA sequenced a few years ago, I was pleased to find out I was above average in that regard, which is undoubtedly why I like my steaks medium-rare and generally run around half-naked when the weather is warm.  Likewise, many people of East Asian, Indigenous Australian, Native American, and Polynesian ancestry have Denisovan ancestry, evidence that those hard-and-fast "containers" aren't so water-tight after all.

The reason all this comes up is because of a new study of the "Petralona Skull," a hominin skull found covered in dripstone (calcium carbonate) in a cave near Thessaloniki, Greece.  The skull has been successfully dated to somewhere between 277,000 and 539,000 years ago -- the uncertainty is because of estimates in the rate of formation of the calcite layers.

The Petralona Skull  [Image licensed under the Creative Commons Nadina / CC BY-SA 3.0]

Even with the uncertainty, this range puts it outside of the realm of possibility that it's a modern human skull.  Morphologically, it seems considerably more primitive than typical Neanderthal skulls, too.  So it appears that there was a distinct population of hominins living in southern Europe and coexisting with early Neanderthals -- one about which paleontologists know next to nothing.

Petralona Cave, where the skull was discovered [Image licensed under the Creative Commons Carlstaffanholmer / CC BY-SA 3.0]

So our family tree turns out to be even more complicated than we'd realized -- and there might well be an additional branch, not in Africa (where most of the diversification in hominins occurred) but in Europe.  

You have to wonder what life was like back then.  This would have been during the Hoxnian (Mindel-Riss) Interglacial, a period of warm, wet conditions, when much of Europe was covered with dense forests.  Fauna would have included at least five species of mammoths and other elephant relatives, the woolly rhinoceros, the cave lion, cave lynx, cave bear, "Irish elk" (which, as the quip goes, was neither), and the "hypercarnivorous" giant dog Xenocyon.  

Among many others.

So as usual, the mischaracterization of science by anti-science types misses the reality by a mile, and worse, misses how incredibly cool that reality is.  The more we find out about our own species's past, the richer it becomes.

I guess if someone wants to dismiss it all with a sneering "why are there still monkeys?", that's up to them.  But me, I'd rather keep learning.  And for that, I'm listening to what the scientists themselves have to say.

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Life, not as we know it

I've written here before about unusual paleontological discoveries -- illustrations of the fact that Darwin's lovely phrase "many forms most beautiful and most wonderful" has applied throughout Earth's biological history.

We could also add the words "... and most weird."  Some of the fossils paleontologists have uncovered look like something from a fever dream.  A while back I wrote about the absolutely bizarre "Tully Monster" (Tullimonstrum spp.) that is so different from all other life forms studied that biologists can't even figure out whether it was a vertebrate or an invertebrate.  But Tully is far from the only creature that has defied classification.  Here are a few more examples of peculiar organisms whose placement on the Tree of Life is very much up for debate.

First, we have the strange Tribrachidium heraldicum, a creature of uncertain relationships to all species at the time or afterward.  It had threefold symmetry -- itself pretty odd -- and its species name heraldicum comes from the striking resemblance to the triskelion design on the coat of arms of the Isle of Man:

Tribrachidium fossil from near Arkhangelsk, Russia [Image licensed under the Creative Commons Aleksey Nagovitsyn (User:Alnagov), Tribrachidium, CC BY-SA 3.0]

Despite superficial similarities to modern cnidarians (such as jellyfish) or echinoderms (such as sea urchins and starfish), Tribrachidium seems to be neither.  It -- along with a great many of the Ediacaran assemblage, organisms that dominated the seas during the late Precambrian Era, between 635 and 538 million years ago -- is a mystery.

The Ediacaran is hardly the only time we have strange and unclassifiable life forms.  From much later, during the Carboniferous Period (on the order of three hundred million years ago), the Mazon Creek Formation in Illinois has brought to light some really peculiar fossils.  One of the most baffling is Etacystis communis, nicknamed the "H-animal":

Reconstruction of Etacystis [Image is in the Public Domain]

It's an invertebrate, but otherwise we're still at the "but what the hell is it?" stage with this one.  Best guess is it might be a distant relative of hemichordates ("acorn worms"), but that's speculative at best.

Next we have Nectocaris.  The name means "swimming shrimp," but a shrimp it definitely was not.  It next was thought to be some kind of primitive cephalopod, perhaps related to cuttlefish or squid, but that didn't hold water, either.  They had a long fin down each side that they probably used for propulsion, and a feeding tube shaped like a funnel (that you can see folded to the left in the photograph below):

Photograph of a Nectocaris fossil from the Burgess Shale Formation, British Columbia [Image is in the Public Domain]

All of the Nectocaris fossils known come from the early Cambrian.  It's possible that they were a cousin of modern chaetognaths ("arrow worms"), but once again, no one is really sure.

Another Cambrian animal that has so far defied classification is Allonnia, which was initially thought to be related to modern sponges, but their microstructure is so different they're now placed in their own order, Chancelloriidae.  You can see why the paleontologists were fooled for a while:

Reconstruction of Allonnia from fossils recovered from the Chengjiang Formation, Yunnan Province, China [Image licensed under the Creative Commons, Yun et al. 2024 f05 (preprint), CC BY 4.0]

At the moment, Allonnia and the other chancelloriids are thought to represent an independent branch of Kingdom Animalia that went extinct in the mid Cambrian Era and left no descendants -- or even near relatives.

Last, we have the bizarre Namacalathus hermanestes, which has been found in (very) late Precambrian shales in such widely-separated sites as Namibia, Canada, Paraguay, Oman, and Russia.  Check out the reconstruction of this beast:

[Image credit Zhuravlev, Wood, and Penny, Proceedings of the Royal Society B, November 2015]

It's been tentatively connected to lophophorates (which include the much more familiar brachiopods), but if so, it must be a distant relationship, because they look a great deal more like something H. P. Lovecraft might have dreamed up:

Unlike the, um, "Yuggothians," though, Namacalathus was quite real.  And, apparently, widespread.

The early Cambrian seas must have contained plenty of nightmare fuel.

And those are just five examples of organisms that would have certainly impelled Dr. McCoy to say, "It's life, Jim, but not as we know it."  Given how infrequently organisms fossilize -- the vast majority die, decay away, and leave no traces, and the vagaries of geological upheaval often destroy the fossil-bearing strata that did form -- you have to wonder what we're missing.  Chances are, for every one species we know about, there are hundreds more we don't.

What even more bizarre life forms might we see if we actually went back there into the far distant past?

I guess we'll have to wait until someone invents a time machine to find out.

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Old as the hills

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

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

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

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

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

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

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

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

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

Better known as glass.

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

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

There are two other reasons Pilbara is remarkable.

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

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

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

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

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

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Mental models and lying stones

Richard Feynman famously said, "The first principle is that you must not fool yourself -- and you are the easiest person to fool."

This insightful statement isn't meant to impugn anyone's honesty or intelligence, but to highlight that everyone -- and I'm sure Feynman was very much including himself in this assessment -- has biases that prevent them from seeing clearly.  We've already got a model, an internal framework by which we interpret what we experience, and that inevitably constrains our understanding.

As science historian James Burke points out, in his brilliant analysis of the scientific endeavor The Day the Universe Changed, it's a trap that's impossible to get out of.  You have to have some mental model for how you think the world works, or all the sensory input you receive would simply be chaos.  "Without a structure, a theory for what's there," Burke says, "you don't see anything."

And once you've settled on a model, it's nearly impossible to compromise with.  You're automatically going to take some things as givens and ignore others as irrelevant, dismiss some pieces of evidence out of hand and accept others without question.  We're always taking what we experience and comparing it to our own mental frameworks, deciding what is important and what isn't.  When my wife finished her most recent art piece -- a stunning image of a raven's face, set against a crimson background -- and I was on social media later that day and saw another piece of art someone had posted with a raven against red -- I shrugged and laughed and said, "Weird coincidence."

Quoth the Raven, pen/ink/watercolor by Carol Bloomgarden (2025) [Image used with permission]

But that's only because I had already decided that odd synchronicities don't mean anything.  If I had a mental model that considered such chance occurrences as spiritually significant omens, I would have interpreted that very, very differently.

Our mental frameworks are essential, but they can lead us astray as often as they land us on the right answer.  Consider, for example, the strange, sad case of Johann Beringer and the "lying stones."

Johann Bartholomeus Adam Beringer was a professor of medicine at the University of Würzburg in the early eighteenth century.  His training was in anatomy and physiology, but he had a deep interest in paleontology, and had a large collection of fossils he'd found during hikes in his native Germany.  He was also a devout Lutheran and a biblical literalist, so he interpreted all the fossil evidence as consistent with biblical events like the six-day creation, the Noachian flood, and so on.

Unfortunately, he also had a reputation for being arrogant, humorless, and difficult to get along with.  This made him several enemies, including two of his coworkers -- Ignace Roderique, a professor of geography and algebra, and Johann Georg von Eckhart, the university librarian.  So Roderique and von Eckhart hatched a plan to knock Beringer down a peg or two.

They found out where he was planning on doing his next fossil hunt, and planted some fake fossils along the way.

These "lying stones" are crudely carved from limestone.  On some of them, you can still see the chisel marks.

More outlandish still, Roderique and von Eckhart carved the word "God" in Hebrew on the backs of some of them.  Making it look like the artisan had signed His name, so to speak.

One colleague -- who was not in on the prank -- looked at the stones, and said to Beringer, "Um... are you sure?  Those look like chisel marks."  Beringer dismissed his objections, and in fact, turned them into evidence for his explanation.  Beringer wrote, "...the figures... are so exactly fitted to the dimensions of the stones, that one would swear that they are the work of a very meticulous sculptor...[and they] seem to bear unmistakable indications of the sculptor's knife."

They were so perfect, Beringer said, that they could only be the work of God.

So as astonishing as it may seem, Beringer fell for the ruse hook, line, and sinker.  Roderique and von Eckhart, buoyed up by their success, repeated their prank multiple times.  Finally Beringer had enough "fossils" that in 1726, he published a scholarly work called Lithographiae Wirceburgensis (The Writing-Stones of Würzburg).  But shortly after the book's publication -- it's unclear how -- Beringer realized he'd been taken for a ride.

He sued Roderique and von Eckhart for defamation -- and won.  Roderique and von Eckhart were both summarily fired, but it was too late; Beringer was a laughingstock in the scientific community.  He tried to recover all of the copies of his book and destroy them, but finally gave up.  His reputation was reduced to rubble, and he died twelve years later in total obscurity.

It's easy to laugh at Beringer's credulity, but the only reason you're laughing is because if you found such a "fossil," your mental model would immediately make you doubt its veracity.  In his framework -- which included a six-thousand-year-old Earth, a biblical flood, and a God who was perfectly capable of signing his own handiwork -- he didn't even stop to consider it.

The history of science is laden with missteps caused by biased mental models.  In 1790, a report of a fireball over France that strewed meteorites over a large region prompted a scientific paper -- that laughingly dismissed the claim as "impossible."  Pierre Bertholon, editor of the Journal des Sciences Utiles, wrote, "How sad, is it not, to see a whole municipality attempt to certify the truth of folk tales… the philosophical reader will draw his own conclusions regarding this document, which attests to an apparently false fact, a physically impossible phenomenon."  DNA was dismissed as the genetic code for decades, because of the argument that DNA's alphabet only contains four "letters," so the much richer twenty-letter alphabet of proteins (the amino acids) must be the language of the genes.  Even in the twentieth century, geologists didn't bother looking for evidence for continental drift until the 1950s, long after there'd been significant clues that the continents had, in fact, moved, largely because they couldn't imagine a mechanism that could be responsible.

Our mental models work on every level -- all the way down to telling us what questions are worth investigating.

So poor Johann Beringer.  Not to excuse him for being an arrogant prick, but he didn't deserve to be the target of a mean-spirited practical joke, nor does he deserve our derision now.  He was merely operating within his own framework of understanding, same as you and I do.

I wonder what we're missing, simply because we've decided it's irrelevant -- and what we've accepted as axiomatic, and therefore beyond questioning?

Maybe we're not so very far ahead of Beringer ourselves.

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Creepy crawlies

Whenever we have a wet summer -- not an uncommon occurrence in our rainy climate -- we have a plague of little pests trying to get into our house.

They're called millipedes, slinky guys maybe a couple of centimeters long, with lots of legs (not a thousand, though).  They're completely harmless; they don't bite like their cousins the centipedes do, and if you poke at them, they coil up into a ball.  So I guess they're really more of a nuisance than an actual problem.  They don't even damage anything, the way mice can.  Mostly what they seem to do is get in through every crack and crevice (there are lots of these in a big old house like ours), look around for a while, then curl up and die.

[Image licensed under the Creative Commons Totodu74, Anadenobolus monilicornis 03, CC BY-SA 3.0]

So I don't like them, and I wish they stayed outside, but in the grand scheme of things they're no big deal.  Imagine, though, if they were bigger.

A lot bigger.

Recently, paleontologists announced the discovery on a beach in Northumberland, England, of a millipede fossil from the Carboniferous Period.  It's been dated to the middle of the period, about 326 million years ago.  It looks a bit like the millipedes I see trundling across my basement floor in summer.

Only this one was 2.6 meters long (approximately the length of a Mini Cooper), a half a meter across, and weighed something on the order of fifty kilograms.

It's been named Arthropleura, and holds the record as the largest-known arthropod in Earth's history.  Nothing is known for sure about its behavior; if it's like the rest of millipedes, it was a scavenger on leaf detritus, but there's no way to know for certain.  Given its size, it could well have been a lot more dangerous than the ones we have around now.  To paraphrase the old joke about five-hundred-pound gorillas:

Q: What does a fifty-kilogram millipede eat?

A: Anything it wants.

Those of you who are (like me) biology nerds may be frowning in puzzlement at this point.  How on earth could an arthropod get so big?  Their size is limited by the inefficiency of their respiratory system (not to mention the weight of their exoskeletons).  Most arthropods (millipedes included) breathe through pairs of holes called spiracles along the sides of the body.  These holes open into a network of channels called tracheae, which bring oxygen directly to the tissues.  Contrast that with our system; we have a central oxygen-collecting device (lungs), and the hemoglobin in our blood acts as a carrier to bring that oxygen to the tissues.  It's a lot more efficient, which is why the largest mammals are a great deal bigger than the largest arthropods.  (So, no worries that the bad sci-fi movies from the 50s and 60s, with giant cockroaches attacking Detroit, could actually happen.  A ten-meter-long cockroach not only wouldn't be able to oxygenate its own tissues fast enough to survive, it couldn't support its own weight.  It wouldn't eat Detroit, it would just lie there and quietly suffocate.)

So how could there be such ridiculously enormous millipedes?

The answer is as fascinating as the beast itself is.  As the temperature warmed and rainfall increased after the previous period (the Devonian), it facilitated the growth of huge swaths of rain forest across the globe.  In fact, it's the plant material from these rain forests that produced the coal seams that give the Carboniferous its name.  But the photosynthesis of all these plants drove the oxygen levels up -- by some estimates, to around 35% (contrast that to the atmosphere's current 21% oxygen).  This higher oxygen level facilitated the growth of animals who are limited by their ability to uptake it -- i.e., arthropods. (At the same time, there was a dragonfly species called Meganeura with a seventy-centimeter wingspan.  And unlike millipedes, these things were carnivores, just as modern dragonflies are.)

Eventually, though, the system was unsustainable, and a lot of the rain forests began to die off in the Late Carboniferous, leading to a drier, cooler climate.  However, remember the coal seams -- by that time a huge percentage of the carbon dioxide that had fed the photosynthesis of those rain forests was now locked underground.  The fuse was lit for a catastrophe.

Fast forward to the end of the next period, the Permian, 255 million years ago.  What seems to have happened is a series of colossal volcanic eruptions that created the Siberian Traps, a basalt deposit covering most of what is now Siberia.  The lava ripped through the coal seams, blasting all that stored carbon into the atmosphere as carbon dioxide.  The temperature in the late Permian had been cool and dry, and the spike of carbon dioxide created a commensurate spike in the temperature -- as well as a huge drop in oxygen, used up by the burning coal.  The oxygen concentration seems to have bottomed out at around twelve percent, just over half of what it is now.  The extra carbon dioxide dissolved into ocean water, dropping the pH, and the increasing acidity dissolved away the shells of animals who build them out of calcium carbonate -- e.g. corals and mollusks.

Wide swaths of ocean became anoxic, acidic dead zones.  The anaerobic organisms began to eat through all the dead organic matter, churning out more carbon dioxide and another nasty waste product, sulfur dioxide (which gives the horrible smell to rotten eggs, and is also an acidifier).  The result: an extinction that wiped out an estimated ninety percent of life on Earth. In short order, a thriving planet had been turned into a hot, dead, foul-smelling wasteland, and it would take millions of years to recover even a fraction of the previous biodiversity.

Of course, at highest risk would be the big guys like our friends Arthropleura and Meganeura, and the Earth hasn't seen giant arthropods like this since then.  Today, the largest arthropod known is the Japanese spider crab (Macrocheira), topping out at around twenty kilograms -- but crabs and other crustaceans have gills and an oxygen carrier called hemocyanin, so they can boost the efficiency of their respiratory system somewhat over their terrestrial cousins.  The largest insect today is the African Goliath beetle (Goliathus), at about a tenth of a kilogram.  And in today's atmosphere, it's at a pretty significant disadvantage.  They may look big and scary, but in reality, they're slow-moving, harmless creatures.  Kind of a beer can with six legs, is how I think of them.

So that's today's look at creepy-crawlies of the past.  In my opinion it's just as well the big ones became extinct. The last thing I need is having to shoo a fifty-kilogram millipede out of my basement.

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