A Cambrian holdout

Although you don't tend to hear much about it, the Ordovician Period was a very peculiar time in Earth's history.

From beginning (485 million years ago) to the end (444 million years ago) it experienced one of the biggest global climatic swings the Earth has ever seen.  In the early Ordovician the climate was a sauna -- an intense greenhouse effect caused the highest temperatures the Paleozoic Era would see, and glacial ice all but vanished.  By the end, the center of the supercontinent of Gondwana was near the South Pole, and glaciers covered much of what is now Africa and South America, resulting in a massive extinction that wiped out an estimated sixty percent of life on Earth.

At this point, life was confined to the oceans.  The first terrestrial plants and fungi wouldn't evolve until something like twenty million years after the beginning of the next period, the Silurian, and land animals only followed after that.  So during the Ordovician, the shift in sea level had an enormous impact -- as the period progressed and more and more ocean water became locked up in the form of glacial ice, much of what had been shallow, temperate seas dried up to form cold, barren deserts.  And that was all there was on land -- thousands of square kilometers of rock, sand, and ice, without a single living thing larger than bacteria to be found anywhere.

Somehow, despite the extreme climatic swings that happened during the Ordovician, life in the oceans diversified, and rebounded after the dramatic dieoff at the end.  And along the way, there were some really peculiar life forms.

One of these was discovered not long ago in the Castle Bank Formation in the middle of Wales.  (Ordovician outcrops in Wales are what gave the period its name; the Ordovices were a tribe that lived there around the time of the Roman conquest of Britain.)  The animal was small -- the fossil measures only thirteen millimeters from tip to tail -- but it was one odd-looking critter:

A reconstruction of Mieridduryn bonniae [Image credit: Franz Anthony]

Aficionados of paleontology will no doubt immediately recognize the similarity to Cambrian animals called Opabinia and Anomalocaris; Mieridduryn looks almost like a hybrid of the two.  (If you're a linguistics geek like myself, you might be interested to know that the genus name Mieridduryn comes from Welsh words meaning "bramble snout.")  And it does seem to be a holdover from the Cambrian Explosion fauna, which also produced such weird forms as Hallucigenia (the name means "comes from a hallucination"), which is so bizarre that at first, paleontologists reconstructed it upside down, until some better-preserved fossils made them realize their error.

[Image licensed under the Creative Commons Qohelet12, Hallucigenia, CC BY-SA 4.0]

By the Ordovician, however, a lot of the stranger (to our eyes, at least) life forms had gone extinct, and the wipeout at the end of the Ordovician finished off the last of them.  At that point, what was left -- arthropods, primitive vertebrates, mollusks, echinoderms, annelids, and so on -- would have begun to look a lot more familiar to us.

But during the mid-Ordovician, when Mieridduryn was snorking about in the mud of shallow, warm oceans, there were still some mighty peculiar animals.  If you hopped a time machine and went back there, you might well think you were on a different planet.  It reminds me of the poem by Irish geologist John Joly, which he was inspired to write while looking at a the fossil of a long-extinct animal, and seems a fitting place to end:

Is nothing left?  Have all things passed thee by?

The stars are not thy stars.  The aged hills

Are changed and bowed beneath the ills

Of ice and rain, of river and sky;

The sea that riseth now in agony

Is not thy sea.  The stormy voice that fills

This gloom with man's remotest sorrow shrills

The memory of thy lost futurity.

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A circle of light

The Ordovician Period was a strange time in Earth's (pre)history.

It lasted a little over forty million years, from about 485 million years ago to 444 million years ago.  Coming out of the Cambrian Period, there was incredible diversity in marine life, especially invertebrates like arthropods, mollusks, and brachiopods; and at the beginning it was very hot -- not far off from the Paleocene-Eocene Thermal Maximum, which had a global average temperature almost ten degrees higher than it is today.  But over the next forty million years, the climate went into a slow slide, ending with what is called the "Hirnantian Icehouse," a period of widespread continental glaciation.  The climate shift triggered a mass extinction, one of the "Big Five," and an estimated eighty percent of marine species went extinct.

But unlike the later Permian-Triassic and Cretaceous Extinctions, this one wasn't at all sudden -- suggesting that the causes of the other two mentioned, a massive volcanic eruption and an asteroid strike respectively, might not have been responsible.

So what triggered the climatic shift and die-off?

One thing was simply plate movement; by the end of the Ordovician, Gondwana (what is now Africa, South America, Antarctica, and Australia) were near the South Pole, which led to the formation of glaciers.  But it's hard to see how that by itself would have had such an enormous effect on life worldwide.

A paper this week in Earth and Planetary Science Letters proposes a curious solution, hinging on a peculiar observation; there was a meteorite barrage around 466 million years ago, during the middle of the Ordovician.  Extant rocks of that age show dozens of impact craters.  But... those craters are almost entirely limited to regions that were within thirty degrees of the equator at the time.

The researchers estimate that the likelihood of that occurring by chance is equivalent to flipping a coin 21 times and getting tails every time.  But if they were connected, there's the problem that the extinction didn't occur right after the barrage; there was an almost twenty million year gap between the impact array and the icehouse/extinction.  It's apparent that the strikes didn't directly trigger the extinction.

What the researchers propose is a near strike by a large asteroid -- one that, had it hit square on (as the Chicxulub Meteorite would do almost exactly four hundred million years later) would have been in the planet-killer category.  But it did pass inside the Roche limit, the distance a smaller object can pass a planet at which the gravity holding the passing asteroid together is exceeded by the tidal forces trying to tear it apart.

So rather than going into orbit, or crashing into the Earth in one piece, the asteroid got shredded.  The larger chunks went into decaying trajectories and ultimately impacted Earth near their orbital planes (parallel to the Earth's equator -- resulting in the odd distribution of craters), and the rest got spun out into...

... a ring system.

[Image credit: Oliver Hull]

The researchers think the rings shaded the Earth from enough of the Sun's warmth and light that it precipitated a slow decline into an ice age, and coupled with the movement of a big section of the Earth's crust down to near the South Pole, a worldwide icehouse.  But because it was a gradual drop in temperature, the hit on biodiversity didn't happen all at once -- although by the end, it certainly was big enough to rank amongst the largest mass extinctions ever.

But -- a ring system.  Can you imagine what that'd have looked like?

Of course, it's not like taking a time machine back to the late Ordovician would be all that hot an idea, and I mean that both literally and figuratively.  Notwithstanding how gawdawful cold it'd have been, there would also be the problem of finding food.  Plants had yet to colonize the land -- that wouldn't happen until the next geological period, the Silurian -- so the continents were basically one barren expanse of rock, dirt, and sand. 

But still.  Standing there in that empty landscape, and you look up, and arching over your head, spanning the entire dome of the sky, are these broad rings, a circular belt shining in reflected light.

We used to think rings were uncommon; for a long time, Saturn was the only planet known to have them.  But better telescopes and (especially) flybys have found ring systems around all four of the gas giants.  Now, if the current paper bears up under scrutiny, we might add Earth to the list.  Eventually, the Earth's ring system scattered and decayed away -- gravitational interactions between multiple objects of similar sizes are inherently unstable -- allowing the Earth to warm again, leading into the swampy, hot Silurian and Carboniferous Periods.

But for a while, we had what must have been an awe-inspiring adornment.

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Bugs of unusual size

Although you don't tend to hear much about it, the Ordovician Period was a very peculiar time in Earth's history.

From beginning (485 million years ago) to the end (444 million years ago) it experienced one of the biggest global climatic swings the Earth has ever seen.  In the early Ordovician the climate was a sauna -- an intense greenhouse effect caused the highest temperatures the Paleozoic Era would see, and glacial ice all but vanished.  By the end, the center of the supercontinent of Gondwana was near the South Pole, and glaciers covered much of what is now Africa and South America, resulting in a massive extinction that wiped out an estimated sixty percent of life on Earth.

At this point, life was confined to the oceans.  The first terrestrial plants and fungi wouldn't evolve until something like twenty million years after the beginning of the next period, the Silurian, and land animals only followed after that.  So during the Ordovician, the shift in sea level had an enormous impact -- as the period progressed and more and more ocean water became locked up in the form of on-land glacial ice, much of what had been shallow, temperate seas dried up to form cold, barren deserts.

But during the beginning of the period, life thrived in the warm oceans, giving rise to huge ecosystems based on reef-building corals and sponges.  Just as today, back then coral reefs provided habitats to a tremendously diverse community, and fossil beds like the Fezouata Formation of Morocco give us a glimpse of a strange and wonderful world.

Here's one of the exceptionally well-preserved fossils from Fezouata, a marrellomorph arthropod called Furca mauritanica:

[Image licensed under the Creative Commons Didier Descouens, Furca mauritanica MHNT, CC BY-SA 3.0]

And here's a reconstruction of another one from the same group, the bizarre Mimetaster hexagonalis (the genus name means "mimics a starfish"):

[Image licensed under the Creative Commons Franzanth, Mimetaster hexagonalis reconstruction, CC BY-SA 4.0]

These arthropods, more closely related to trilobites than to any living species, were one of the dominant groups during the temperate early Ordovician, but had vanished almost entirely during the icehouse conditions of the end of the period.  

The reason this comes up is because of a paper out of the University of Exeter about further research into the fossils of the Fezouata Formation.  And this study has turned up something phenomenal -- another kind of marrellomorph arthropod related to Furca and Mimetaster that was something on the order of two meters long.

That is one big swimming bug.

I found this a little surprising, above and beyond simply being shocking because it's enormous.  As far as I understand physical chemistry, I would think that the greenhouse conditions of the early Ordovician implied two things: (1) higher carbon dioxide and lower oxygen levels, both in the atmosphere and the oceans; and (2) the warmer temperatures making what oxygen there was less soluble in water.  Both of these would lead to more hypoxic conditions, and -- again, as far as my layperson's understanding goes -- should result in generally smaller body size, especially in arthropods.

Arthropods have a couple of limitations that keep cockroaches from getting big as elephants (despite what you might have seen in any number of bad 1950s horror movies).  First, they aren't built to support a large body mass; a terrestrial insect expanded to enormous size, with its bodily proportions left intact, wouldn't be able to stand up, much less move.  This disadvantage is somewhat offset by living in the water, where buoyancy supports the body's mass.  (Note how much bigger oceanic mammals can get than terrestrial ones do.)

Second, and more apposite to this discussion, arthropods are limited by their rather shoddy respiratory systems.  They don't circulate oxygen using their blood, as we do; oxygen is absorbed passively, through channels called tracheal tubes (in terrestrial arthropods) and feathery gills (in aquatic ones).  Gills do have an edge, efficiency-wise, over tracheal tubes, but are working against water's much lower oxygen concentration (way less than one percent, as compared to air at sea level, which averages around twenty-one percent).  This is why terrestrial animals drown; their lungs are just not efficient enough to extract oxygen from a fluid that has so little of it.

And, as I said before, the likelihood is that the conditions of the early Ordovician would likely have combined to cause a far lower dissolved concentration in the oceans than we have now.

So how did marrellomorphs get so big?

At the moment, we don't know.  But the new study has shown that the early Ordovician seas were even weirder than we'd thought, with arthropods swimming around as long as a fully-grown human is tall.

No idea what those things ate, but if I ever get in a time machine and go back then, I'm sure as hell going to be careful if I go swimming.

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An ancient invasion

Just about anywhere you are in the world, you are confronted constantly with invasive species.

Some are so ubiquitous we've stopped even noticing them.  Here in the United States, for example, most lawn grasses are non-natives (including, amusingly, Kentucky bluegrass), as are dandelions, daisies, burdock, garlic mustard, multiflora rose, bush honeysuckle, and thistle.  None of our domesticated animals are native to North America, but neither are such ridiculously common creatures as house mice, the various species of rats, Japanese beetles, pigeons, starlings, house sparrows, and goldfish.  

It's tempting to lump all these species together and say "exotic = bad," but that's a vast, and inaccurate, oversimplification.  Some have clearly had devastating effects on native species; feral and owned-but-outdoor cats, for example, kill an estimated two billion birds a year in the United States alone.  (Yes, that's billion, not million.  Cats are responsible for more bird deaths than any other single cause.)  Other exotics have had far less impact; dandelions may be in every lawn in North America, for example, but they don't seem to do much in the way of outcompeting other species.  (And, as I said earlier, lawn grasses are exotics themselves anyhow.)

A lot of effort by environmental agencies has been put into eradication of exotics, to varying levels of success.  Rats and mice, for example, are generally a lost cause, given their fast reproductive rate and ability to survive on damn near any kind of food; but some isolated islands have done pretty well, most notably South Georgia, which wiped out their rat and mouse infestation in 2018 in order to save endangered birds that nest there.

The southeastern United States, however, has had almost zero success controlling kudzu, also called "mile-a-minute vine" because of its stupendous growth rate.  Introduced in 1876, and hailed as a source of browse for cattle and starch-rich roots that could be used in place of potatoes, the vine went on to cover trees, barns, and slow-moving individuals, and to this day blankets acres during its growing season.

Kudzu in Atlanta, Georgia [Image is in the Public Domain]

Where it gets interesting is the observation by one of my AP Environmental Science students a while back, who said, "But if you go back far enough, isn't everything exotic?"  It's a point well taken.  Species move around, and introductions happen by accident pretty much continuously.  (In fact, there's a whole mathematical model called island biogeography that has to do with the effects of such factors as island size and distance from the mainland on immigration rate and stable biodiversity.)  Our own deliberate and accidental introductions are only continuing a process that has been going on for a long time.

A very long time, to judge by the research of Ian Forsythe (of the University of Cincinnati) and Alycia Stigall (of the University of Tennessee - Knoxville).  They've been studying the "Richmondian Invasion" -- a sudden influx of new species into the shallow sea that covered what is now northern Kentucky, southwestern Ohio, and southeastern Indiana that occurred during the Late Ordovician, 450 million years ago.

The invasion was surprisingly rapid.  Due to exceptionally well-preserved strata, they were able to show that the new species were introduced from the north, as rising seas allowed them to cross what had been a low ridge of dry land, over only a few thousand years.  And what Forsythe and Stigall found was despite the magnitude of the invasion, and the speed with which it occurred, it didn't have very much effect on the recipient ecosystem's pre-existing species.

The reason, Forsythe and Stigall say, is that most of the invaders were low on the trophic ladder -- they were filter-feeders and grazers on phytoplankton.  It'd have been a different story if the invaders had been high-trophic-level predators.

All of this should inform our decisions on where to put our limited resources for environmental management.  High-impact, high-trophic-level invaders -- feral cats, rats, and the like -- are more critical to control than low-level herbivores like pigeons and house sparrows.  (It bears mention, though, that just being a herbivore doesn't mean "harmless;" here in the northeastern United States, whole forests of ash trees are being killed by the emerald ash borer, and farmers and viticulturists are rightly flipping out about the wildfire-spread of the spotted lanternfly.)

So it's a complex subject.  But it's fascinating that an analysis of an exotic invasion 450 million years ago might inform our decisions about how to manage exotics today.  Yet another indication of the value of pure research -- it can give us an angle on real-world problems that we wouldn't have arrived at otherwise.

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A rain of dust

One of the problems with the modern industrialized worldview -- and yes, I know this is an overgeneralization, but still -- is our tendency to think we're capable of controlling everything.

I'm not so much talking about simple day-to-day occurrences.  At least on a theoretical level, we're all aware we could get clobbered by a truck while crossing the road.  But the bigger stuff all seems so solid, so unshakeable, that it's hard to imagine it ever changing.  Of course the grocery stores will always have food, there'll always be electricity available when we plug in our toasters, water will flow when we turn on the faucet.  On an even bigger scale -- it'll be warm in the summer and cool in the winter, the crops will grow, the rain will fall.

You don't have to know much science -- or history, for that matter -- to realize how false this attitude is.  Even small perturbations to the global ecosystem can have drastic consequences.  (Just as a handful of examples -- the 1984-1985 drought in Ethiopia that left 1.2 million dead and 400,000 refugees; the drought in the Yucatán in the early 10th century C.E. that is thought to have caused the downfall of the Mayan Empire; and the American Dust Bowl of the 1930s. brought on by drought and lousy farming practices.)

The fact is -- and it's a point I've made before -- we need to be extraordinarily careful in pushing at the global ecosystem, because it can respond catastrophically to purely natural circumstances.  Adding global-scale human foolishness into the equation is a recipe for disaster.

As an example of how distant events can have unexpected global consequences, take the study published last week in Science Advances suggesting that a collision between two asteroids half a billion kilometers away triggered a drastic plunge in temperatures and the initiation of an ice age.  The event, which took place in the mid-Ordovician Period (466 million years ago), involved the destruction of an asteroid on the order of 150 kilometers in diameter, creating a dust plume that rained down upon the Earth.  The dust and debris blocking the sunlight triggered a drop in global temperatures and a sudden (geologically speaking) turnaround in the climate that spread ice sheets over much of the high latitudes in both hemispheres.

Of course, cosmic dust is falling into the Earth's atmosphere all the time, but this event caused a massive spike in the amount.  "Normally, Earth gains about 40,000 tons of extraterrestrial material every year," said study co-author Philipp Heck of the University of Chicago in an interview with Astronomy.  "Imagine multiplying that by a factor of 1,000 or 10,000."

The outcrop in Sweden that the researchers studied.  The layer containing the debris from the collision is visible as a gray line about 2/3 of the way up the cliff face.  [Image courtesy of Philipp Heck and the Field Museum]

The result of the cool-down was a huge increase in biodiversity as life forms evolved to cope with the change.  But before you start in on the "life finds a way" line of thought, and that this'll save us from the consequences of anthropogenic climate change, allow me to point out that the massive Ordovician chill was slower than today's warm-up by orders of magnitude.  "In the global cooling we studied, we're talking about timescales of millions of years," said Heck. "It's very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it's different from the global warming today — this global cooling was a gentle nudge.  There was less stress."

So yeah.  Having a thousand times the amount of dust flung at us from the explosion of an asteroid 150 kilometers across is still not as drastic as what we're currently doing to the climate.

Oh, and in a rather horrid coincidence, that quantity of debris is roughly equal to the amount of plastic we produced in 2015, 79% of which was landfilled.

So the idea that somehow the Earth is obligated to remain hospitable to human life regardless what we do to it -- or what happens outside of our sphere of control -- would be ludicrous if it weren't so terrifying.  It's why ham-handed efforts to "own the libs" by nitwits like Laura Ingraham (who tried to be funny by "attempting to drink a light-bulb stuffed steak using plastic straws") fall flat if you know anything at all about science.

Go ahead, Laura, laugh it up.  You better hope that we "libs" are overestimating the danger posed by the pro-industry, pro-fossil-fuels, damn-the-ecology-full-speed-ahead policies favored by people of your stripe.  And don't even start with me about how environmentally-conscious people are "hoping for disaster" or "trying to destroy the economy."  Fearing that something is likely to happen isn't the same as hoping it will happen, which should be clear to anyone who has an IQ larger than their shoe size and concern for anything other than short-term financial gain.

So once again, we have a piece of research about a distant event millions of years ago providing a cautionary tale about what's happening here and now.  I wish I had some kind of positive note to end this on, but increasingly, it's looking like our current behavior is likely to throw us past a tipping point -- and our long-term legacy might be appearing to some scientist in the distant future as a gray stripe in a rock outcrop.

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This week's Skeptophilia book recommendation is especially for those of you who enjoy having their minds blown.  Niels Bohr famously said, "Anyone who is not shocked by quantum theory has not understood it."  Physicist Philip Ball does his best to explain the basics of quantum theory -- and to shock the reader thereby -- in layman's terms in Beyond Weird: Why Everything You Thought You Knew About Quantum Physics is Different, which was the winner of the 2018 Physics Book of the Year.

It's lucid, fun, and fascinating, and will turn your view of how things work upside down.  So if you'd like to know more about the behavior of the universe on the smallest scales -- and how this affects us, up here on the macro-scale -- pick up a copy of Beyond Weird and fasten your seatbelt.

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