The book was printed sixteen years prior to the first papers that led to what we now know as the plate tectonic model, and what strikes me over and over while looking through it is how close they were to getting it. They had so many of the pieces. Lake and Rastall recognized that volcanoes tend to be much more common in island arcs (such as Indonesia and Japan) and along the edges of continents; they knew all about “the Ring of Fire.” Earthquakes, too, seemed to occur more commonly in those regions. There’s a whole section on places like the East African Rift Valley and the notoriously active area around Naples and Pozzuoli, Italy.

They had been given big hints by scientists like the tragic German geologist and climatologist Alfred Wegener and his South African supporter Alexander du Toit. But the most Lake and Rastall will say is that the topic is “controversial”:

[The cause of vulcanicity] is a large and difficult question and in the present state of our knowledge it is inadvisable to make any dogmatic statements: there are still too many uncertain factors. Up to a certain point the matter is clear: there is no doubt of the close association in space and time of earth movement and igneous activity, both extrusive and intrusive, but it is not always certain which is the cause and which is the effect… This is a very controversial question, and it is not yet possible to attempt an answer.

They even have a whole section on faulting, folding, synclines (places where the rock strata have been forced downward) and anticlines (where they’ve been pushed upward into an arch), and conveniently dance around any consideration of a mechanism for how exactly thousands of kilograms of rock got pushed around, bent, twisted, and in some cases, flipped upside down.

In their defense, that, of course, is the problem; one of the first things a good scientist will demand, when confronted with some kind of proposed explanation of an odd phenomenon, is “Show me the mechanism.” It’s where a lot of fringe-y claims stumble—telepathy and clairvoyance and telekinesis and the like all lack any kind of plausible and rational cause (despite hand-waving arguments about their having something to do with quantum entanglement or the physics of retrocausality). And at the point when Lake and Rastall were writing, we knew next to nothing about the makeup of the Earth’s interior. The magnetometer readings that Hess, Vine, and Matthews used to develop their theory of convective upwelling of magma at mid-ocean ridges, generating seafloor spreading and (finally) providing a motive force for continental drift, were still decades in the future.

Still, it’s impossible to look at Lake and Rastall’s Textbook of Geology and not be struck by the fact that they had nearly all the pieces, and still failed to put together the big picture. After all, it’s not like the basics of plate tectonics are that hard to understand; it’s routinely taught to ninth graders in high school Earth Science classes. But for some reason—whether it was a hidebound acceptance of a static, rather than a dynamic, Earth, or simply an overabundance of caution—Lake, Rastall, and the vast majority of geologists of their generation never got there, and many remained unconvinced by the new model well into the 1970s.

Now, of course, just about everyone accepts it. The evidence has become overwhelming, and it’s only in view of this model that we can explain new data that comes in regularly. This whole topic, in fact, comes up because of a study out of the University of Oxford that was the subject of a paper in Frontiers in Earth Science last week, that analyzed gases bubbling up in an arc of hot springs in Zambia, and found that their chemical composition indicates a source deep in the Earth’s mantle.

The conclusion? The region, called the Kafue Rift, might be in the process of fracturing, and will eventually form a new spreading zone, splitting the southern part of Africa from the rest of the continent.

So this adds another piece to the ongoing breakup of Africa—the more-or-less north-south trending East African Rift, running from Ethiopia to Mozambique, and the east-west trending Kafue Rift, running from Mozambique through Zambia and across Namibia into the Atlantic Ocean. Eventually—and we’re talking millions of years from now—what is now the stable, seemingly solid continent of Africa will very likely be in (at least) three pieces, with inlets of the ocean separating the chunks, and mid-ocean spreading centers down each of the straits like zippers, producing new seafloor and forcing the newly-formed islands apart.

Consideration of how the face of the Earth has changed always puts me in mind of the haunting lines from Alfred, Lord Tennyson’s poem In Memoriam, which seems as fitting a place as any to end:

There rolls the wave where grew the tree.

O Earth, what changes hast thou seen?

There, where the long road roars has been

The stillness of the central sea.

The hills are shadows, and they flow

From form to form, and nothing stands;

They melt like mists, the solid lands,

Like clouds, they shape themselves, and go.

Well, according to a few scientists, philosophers, and deep thinkers, the rabbit hole may go a hell of a lot deeper than that.

Let’s start with Russian self-styled “transhumanist” Alexey Turchin. Turchin has suggested that in order to build a convincing simulated reality, we need not only much more sophisticated hardware and software, we need a much larger energy source to run it than is now available. Emulating one person, semi-convincingly, with an obviously fake animated avatar, doesn’t take much; we can more or less already do that.

But to emulate millions of people, so well that they really are indistinguishable from the people they’re copied from, is a great deal harder. Turchin proposes that one way to harvest that kind of energy is to create a “Dyson sphere“ around the Sun, effectively capturing all of that valuable light and heat that otherwise is simply radiated into space.

Now, I must say that the whole Dyson sphere idea isn’t what grabbed me about Turchin’s paper, as wonderful as the concept is in science fiction (Star Trek aficionados will no doubt recall the TNG episode “Relics,” in which the Enterprise almost got trapped inside one permanently). The technological issues presented by building a Dyson sphere that is stable seem to me to be nearly insurmountable. What raised my eyebrows was his claim that once we’ve achieved a sufficient level of software and hardware sophistication—wherever we get the energy to run it—the beings (can you call them that?) within the simulation would proceed to interact with each other as if it were a real world.

And might not know they were within a simulation.

“If a copy is sufficiently similar to its original to the extent that we are unable to distinguish one from the other,” Turchin asks, “is the copy equal to the original?”

If that’s not bad enough, there’s the even more unsettling idea that not only is it possible we could eventually emulate ourselves within a computer, it’s possible that it’s already been done.

And we’re it.

Work by Nick Bostrom (of the University of Oxford) and David Kipping (of Columbia University) has looked at the question from a statistical standpoint. (Nota bene: David Kipping’s Cool Worlds Lab on YouTube is an absolute must-subscribe if you’re interested in astronomy.) Way back in 2003, Bostrom considered the issue a trilemma. There are three possibilities, he says:

• Intelligent species always go extinct before they become technologically capable of creating simulated realities that sophisticated.

• Intelligent species don’t necessarily go extinct, but even when they reach the state where they’d be technologically capable of it, none of them become interested in simulating realities.

• Intelligent species eventually become able to simulate reality, and go ahead and do it.

Kipping recently extended Bostrom’s analysis using Bayesian statistical techniques. The details of the mathematics are a bit beyond my ken, but the gist of it is to consider what it would be like if choice #3 has even a small possibility of being true. Let’s say some intelligent civilizations eventually become capable of creating simulations of reality. Within that reality, the denizens themselves evolve—we’re talking about AI that is capable of learning, here—and some of them eventually become capable of simulating their reality with a reality-within-a-reality.

Kipping calls such a universe “multiparous”—meaning “giving birth to many.” Because as soon as this ball gets rolling, it will inevitably give rise to a nearly infinite number of nested universes. Some of them will fall apart, or their sentient species will go extinct, just as (on a far simpler level) your character in a computer game can die and disappear from the “world” it lives in. But as long as some of them survive, the recursive process continues indefinitely, generating an unlimited number of matryoshka-doll universes, one inside the other.

[Image licensed under the Creative Commons Stephen Edmonds from Melbourne, Australia, Matryoshka dolls (3671820040) (2), CC BY-SA 2.0]

Then Kipping asks the question that blows my mind: if this is true, then what is the chance of our being in the one and only “base” (i.e. original) universe, as opposed to one of the uncounted trillions of copies?

Very close to zero.

“If humans create a simulation with conscious beings inside it, such an event would change the chances that we previously assigned to the physical hypothesis,” Kipping said. “You can just exclude that [hypothesis] right off the bat. Then you are only left with the simulation hypothesis. The day we invent that technology, it flips the odds from a little bit better than 50–50 that we are real to almost certainly we are not real, according to these calculations. It’d be a very strange celebration of our genius that day.”

My only questions about this—and I’ll admit up front that I’m no expert—have to do with energy availability and fidelity. If the universe really is multiparous (to use Kipping’s term), then the ever-branching ramifications would seem to me to imply an infinite amount of energy in the base world, to support all those nested virtual universes. Physics, as you no doubt know, is uncomfortable with infinities, so this immediately suggests a problem somewhere with the reasoning.

Second, at every tier of the branching tree of virtual universes, wouldn’t you lose some degree of fidelity? You can’t perfectly simulate our universe within even an arbitrarily-large computer; in order to do so, you would need information and processing capacity equal to the universe it’s contained in. So you’d have to cut corners, make some parts of the simulation merely “good enough.” Every time you go up a level, the problem would amplify, until you’d finally have a simulation with poor enough fidelity (or with high enough glitchiness) that it simply wouldn’t be convincing.

On the other hand, the Mandela Effect and Glitch-in-the-Matrix aficionados have a convenient answer to that. So maybe that’s a can of worms to open another day.

The whole thing reminded me of a conversation in my novel Sephirot between the main character, Duncan Kyle, and the fascinating and enigmatic Sphinx, that occurs near the end of the book:

“How much of what I experienced was real?” Duncan asked.

“This point really bothers you, doesn’t it?”

“Of course. It’s kind of critical, you know?”

“Why?” Her basso profundo voice dropped even lower, making his innards vibrate. “Everyone else goes about their lives without worrying much about it.”

“Even so, I’d like to know.”

She considered for a moment. “I could answer you, but I think you’re asking the wrong question.”

“What question should I be asking?”

“Well, if you’re wondering whether what you’re seeing is real or not, the first thing to establish is whether or not you are real. Because if you’re not real, then it rather makes everyone else’s reality status a moot point, don’t you think?”

He opened his mouth, stared at her for a moment, and then closed it again.

“Surely you have some kind of clever response meant to dismiss what I have said entirely,” she said. “You can’t come this far, meeting me again after such a long journey, only to find out you’ve run out of words.”

“I’m not sure what to say.”

The Sphinx gave a snort, and a shower of rock dust floated down onto his head and shoulders. “Well, say something. I mean, I’m not going anywhere, but at some point you’ll undoubtedly want to.”

“Okay, let’s start with this. How can I not be real? That question doesn’t even make sense. If I’m not real, then who is asking the question?”

“And you say you’re not a philosopher,” the Sphinx said, her voice shuddering a little with a deep laugh.

“No, but really. Answer my question.”

“I cannot answer it, because you don’t really know what you’re asking. You looked into the mirrors of Da’at, and saw reflections of yourself, over and over, finally vanishing into the glass, yes? Millions of Duncan Kyles, all looking this way and that, each one complete and whole and wearing the charming befuddled expression you excel at.”

“Yes.”

“Had you asked one of those reflections, ‘Which is the real Duncan Kyle, and which the copies?’ what do you think he would have said?”

“I see what you’re saying. But still… all of the reflections, even if they’d insisted that they were the real one, they’d have been wrong. I’m the original, they’re the copies.”

“You’re so sure?... A man who cannot prove that he isn’t a reflection of a reflection, who doesn’t know whether he is flesh and blood or a character in someone else’s tale, sets himself up to determine what is real.” She chuckled. “That’s rich.”

So yeah. When I wrote that, I wasn’t ready for it to be turned on me personally.

Anyhow, that’s our unsettling science/philosophy for this morning. Right now it’s probably better to go along with Duncan’s attitude of “I sure feel real to me,” and get on with life. But if perchance I am in a simulation, I’d like to appeal to whoever’s running it to let me sleep better at night.

And allow me to add that the analysis by Bostrom and Kipping is not helping much.

You press the rewind button and, making sure you thoroughly erase everything that actually happened, go back to any time and place in the past—say, to the seas of the Burgess Shale. Then let the tape run again and see if the repetition looks at all like the original. If each replay strongly resembles life’s actual pathway, then we must conclude that what really happened pretty much had to occur. But suppose that the experimental versions all yield sensible results strikingly different from the actual history of life? What could we then say about the predictability of self-conscious intelligence? or of mammals?

His point was that a great deal of evolution appears to be contingent—dependent on events and occurrences that would be unlikely to repeat in exactly the same way. And while there’s no way to re-run the tape on the Earth, considering the issue of constraint vs. contingency has profound implications regarding what we’re likely to find elsewhere in the universe. If we did find extraterrestrial life, would we even recognize it if we saw it?

One good example is the fact that terrestrial life is based on carbon—but is that necessarily true everywhere? Sure, carbon’s pretty cool stuff, with its four snazzy valence electrons and all, but maybe there are other ways to build functional organic molecules. The original Star Trek gave a shot at addressing this, with the silicon-based Horta in the episode “The Devil in the Dark.” Silicon, like carbon, has four valence electrons, and thus is capable of bonding into complex rings and chains, and could possibly be the basis of an alternative biochemistry, although its affinity for stabilizing as silica (silicon dioxide), its low solubility in water, and the rigidity of its bonding structure all argue against it being anywhere near as good as carbon.

What about oxygen use? Even here on Earth, we have living things that get by just fine without it; they’re the anaerobes, and include such familiar fermenters as yeast and Lactobacillus acidophilus (the bacteria responsible for yogurt), and such bad guys as the causative agents of tetanus, botulism, and gangrene. Being aerobic certainly seems like a great innovation—it increases the efficiency of a cell’s energy utilization by a factor of eighteen—but it certainly isn’t a requirement. In fact, probably the most common life form on Earth, individual for individual, are methanogens—deep sea-floor bacteria that metabolize anaerobically and produce methane as a waste product. By some estimates, methanogens may outnumber all other living things on Earth put together.

So maybe anaerobic respiration isn’t as efficient as aerobic respiration, but apparently it works well enough.

There are other features that deserve consideration, too. How many of the things we take for granted about animal life are ubiquitous not because they were the result of strong natural selection, but simply because one of our ancestors had those features and happened to be the one that survived? I’m guessing that having the sensory organs, central processing unit (brain), and the mouth clustered together at the anterior end of the animal will turn out to be common; it makes sense to have your perceptive equipment and your feeding apparatus pointing basically in the direction you’re most likely to move. And speaking of movement, how that’s accomplished is probably going to turn out to be fairly uniform everywhere, because there aren’t that many ways to fashion an appendage for walking, flying, or swimming.

But what about symmetry? The vast majority of animals are bilaterally symmetric, meaning that there’s only one axis of symmetry that divides the animal into mirror-image halves. (A few have radial symmetry, where any line through the center works—jellyfish being the most obvious example.) Even animals like starfish, that seem to have some weird five-way symmetry, are actually bilateral; it’s obvious if you look at starfish larva, and in fact is given away by the position of the sieve plate (the opening through which they draw in water), which is off-center.

True multiple-line symmetry doesn’t seem to exist in the animal world, and even in science fiction most aliens are depicted as being nicely bilateral. An exception are the Antarctic Elder Things, an invention of H. P. Lovecraft, which have pentaradial symmetry—further illustrating that as unpleasant a person as Lovecraft evidently was, he had a hell of an imagination.

[Image licensed under the Creative Commons Tom Ardans - blog - Facebook, Old One by Tom Ardans, CC BY-SA 3.0]

So are most animals bilateral because it’s got some kind of selective advantage, or simply because we descend from bilateral creatures who survived well for other reasons? In other words, is it selected for, or an accidental neutral mutation?

One clue in all this, at least for life here on Earth, is a discovery in South Australia that was described in a paper a while back in Proceedings of the National Academy of Sciences. Paleontologists found a fossil half the size of a grain of rice that is over half a billion years old, and is the oldest truly bilateral animal ever found—meaning what we’re looking at may be a very close cousin to the ancestor of all the current bilateral animals on Earth.

In “Discovery of the Oldest Bilaterian from the Ediacaran of South Australia,” by Scott D. Evans and Mary L. Droser (of the University of California-Riverside), Ian V. Hughes (of the University of California-San Diego), and James G. Gehling (of the South Australia Museum Department of Paleontology), we read about Ikaria wariootia, a teardrop-shaped critter whose unprepossessing appearance belies its significance. This tiny little proto-worm might actually be our great-great-great (etc. etc. etc.) grandparent.

The impressions left by Ikaria wariootia [Image credit: Scott D. Evans, UCR]

Not only was it bilateral, it had a throughput digestive system (two openings, one-way flow of material), another innovation that has turned out to be pretty important. “One major difference with a grain of rice is that Ikaria had a large and small end,” said study lead author Scott Evans, in an interview with The Guardian. “This may seem trivial but that means it had a distinct front and back end, which is the kind of organization that leads to the variety of things with heads and tails that are around today.”

Of course, this doesn’t solve the question of whether bilateral symmetry is constrained or not. My guess is that if it turns out to be, it will be because mirror-symmetry is easier to produce genetically. A lot of the homeotic genes (genes that guide the development of overall body plan) work by creating a gradient of some chemical or another, so the polarity of structures is established (head here, butt there, and so forth). It might simply be easier to establish a one-way gradient, with a high on one end and a low on the other, than one with multiple highs and lows arranged symmetrically.

Although we do manage to do a five-point gradient in the development of our fingers and toes, so it’s doable. It just may not be common.

In any case, here we have a creature that may be the reason we’re arranged bilaterally, whether or not it gives us any sort of advantage. Kind of humbling that we might come from a millimeter-wide burrowing scavenger. I guess that’s okay, though, if it’ll keep humanity from getting any cockier than it already is.

There are all the possibilities during recorded history, some of which would be dramatically worse than others (depending, of course, on exactly where you decided to go). Southeastern Europe in the mid-fifth century C.E. would be a poor choice, for example, given the fact that Attila the Hun was kind of trampling the place, causing chaos amongst the Goths (who were already there) and the Romans (who wished the whole lot of them would just go away). Just about anywhere and any time, of course, would have been worse if you were poor; the “nasty, poor, brutish, and short” quip about people’s lives in the past is all too accurate, and worse still if you didn’t have privilege (a condition that sadly hasn’t changed much).

But if you could add in prehistoric times, there are choices that would be a great deal more dire than any time in recorded history. And that’s even assuming you’re eliminating periods prior to the Great Oxidation Event, when the Earth’s atmosphere would have killed you rapidly if you didn’t think to bring along an oxygen supply. Likewise, let’s put out of the running the Late Ordovician (Hirnantian) Glaciation, when damn near the entire Earth was covered in glacial ice, and events like the Chicxulub Meteorite Collision. Hard to imagine how we could survive either one of those.

One time period that often comes up in these discussions is the Carboniferous. This was the era of the enormous arthropods—dragonflies like Meganeura with its 75-centimeter wingspan, and the two-meter-long millipede Arthropleura—which are thought to have evolved because of the favorable conditions of warmth, moisture, and an oxygen concentration in the atmosphere that may have exceeded thirty percent. But honestly, there’s no certainty these things would have been all that dangerous to something the size of a human; so other than the “ooh, icky, creepy-crawlies with lots of legs” issue, the Carboniferous would probably not have been all that bad.

For my money, the odds-on winner is the mid- to late-Cretaceous. Not, perhaps, for the reason you’re thinking; that period of Earth’s (pre)history always brings to mind the Tyrannosaurus rex and the Velociraptor, which were certainly scary beasts. But they are far from the only thing you’d have to worry about, should your space-time machine drop you off there.

I wrote just last month about the Kem Kem Formation in Morocco, a shale and limestone deposit formed when that part of the world was a shallow ocean, and what is now the Sahara was a tropical rain forest. This place was, to put not too fine a point on it, a fucking nightmare. It was home to the schoolbus-sized theropod Carcharadontosaurus, which had twenty-centimeter teeth serrated like steak knives; twenty-meter long crocodilians like Aegisuchus; and the pterodactyloid Apatorhamphus, with a five-meter wingspan and dozens of needle-sharp teeth.

Carcharodontosaurus skull [Image licensed under the Creative Commons Matthew Deery, Ultimate Dinosaurs Carcharodontosaurus, CC BY 2.0]

Oh, so don’t head to Morocco, then! We’d be fine! Right?

Not really. The region bordering the Western Interior Seaway, which bisected North America from north to south during the same time period (and is why Montana, the Dakotas, Nebraska, and Kansas are such great places to find fossils), was no better. There was a horrific fish called Xiphactinus that was five meters long. The Seaway was also home to mosasaurs, carnivorous reptiles that could get to be over twice that length. The plesiosaurs, whose shape will be familiar to aficionados of the Loch Ness Monster, were larger still.

If you were to visit the Cretaceous, going for a nice skinnydip would not be recommended.

Xiphactinus skeleton [Image licensed under the Creative Commons Jonathan Chen, Xiphactinus AMNH, CC BY-SA 4.0]

The reason this stuff all comes up is a rather ghastly set of fossils from that time period that was the subject of a paper in Nature this week. A group of paleontologists, let by Jongyoon Jung of the University of Texas - Austin, discovered sets of tracks at a Cretaceous-age site in South Korea. One of the sets has been analyzed and found to come from an azhdarchid pterosaur that is new to science. The team named it Jinjuichnus procerus, and from its tracks they’ve concluded that it (1) seems to have come down to the ground to hunt, (2) walked on its knuckles while it was doing so, and (3) had an eight-meter wingspan. If that’s not bad enough, there’s a second set of tracks, from an small unidentified terrestrial vertebrate. The two sets of tracks intersect, and there’s a confused mess of marks at their intersection.

Guess what that means.

If our imaginations weren’t bad enough, the scientists have kindly provided us with the following artist’s rendition of the event:

Jinjuichnus and what is about to be an ex-small-unidentified-terrestrial-vertebrate [Image credit: artist Jun Seung Yi, Creative Commons CC BY 4.0 License]

Just in case you needed some more fuel for your dreams tonight.

So. Yeah. Dinosaur enthusiast though I am, I would not jump at the chance for a trip back to the Cretaceous. In fact, considering what I know about most of Earth’s geological time periods, I think I’ll stay put right here where there are not many creatures with Big Nasty Pointy Teeth, and there are nice features like modern medicine, water purification systems, and indoor plumbing.

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