A Radius, an Ulna, 65 Million Years, and Me

Sometimes, to paraphrase F. Scott Fitzgerald, you gaze upon something commensurate to your capacity for wonder. The thing might itself be unimposing, even unlikely to distract the casual observer, yet, after only a little thought, almost overwhelming in its implications. One might feel this way while discerning a fibonacci series in the structure of a seashell, or looking up at a moving dot in the night sky, knowing it to be a space station that would weigh 450 tons down here on the ground. I find myself prone to these moments. It’s part gift, part affliction, and either part symptom or part cause of my tendency towards melancholy. The Big Picture can make you feel pretty small.

For some reason, today, I was remembering one of those times of feeling suddenly overawed by the sheer scope of things, during a visit to Chicago’s Field Museum, a museum of natural history broadly similar to the more famous one in New York. One of the Field’s prize exhibits is an almost complete fossil skeleton of a Tyrannosaurus Rex, which loomed over visitors in the main gallery, still looking thoroughly deadly, that had been dubbed “Sue” because somehow, paleontologists are able to discern gender in the remains of large predatory Dinosaurs.

Upstairs, in the gallery overlooking Sue’s skeleton, was mounted a life-size replica of one of her forelimbs, the ones that seem puzzlingly small and useless, but were obviously used for something, being well-muscled and equipped with terrible claws (sex and mating is always a good bet when trying to explain apparently pointless physiology in animals). It pretty much stopped me in my tracks. It amazed me. In size and architecture it was almost exactly like my own, save for the scythes mounted where I have fingers and an opposable thumb. In the 65 million years of evolution that separated my mammal kin from this reptile, we’d developed virtually the same arms.

If ever, I thought, you wanted simple and direct evidence of Darwin’s theory of evolution, there it was. All living things are related, and all use the same genetic and evolutionary bag of tricks as they struggle to maintain their place in the global ecosystem.

It got me to thinking about how much more we know now than Darwin could have, when On the Origin of Species was first published in 1859. It was only 20 years earlier when a British naturalist named Richard Owen first realized that certain strange fossil bones must have belonged to a previously unknown line of creatures, for which he coined the term “Dinosauria”, Greek for “terrible lizards”. By the late 1800s rival American fossil hunters named Cope and Marsh were engaged in a heated competition of almost manic Dinosaur harvesting, discovering and classifying many dozens of new species, and in the mad rush – really, these guys were more like unscrupulous treasure hunters than scientists – mistakes were made, including the mounting by Marsh of the wrong fossil head on a Brontosaurus skeleton, an error that wasn’t rectified until 1979. That wasn’t such a big boo-boo; Cope once mounted a fossil head at the end of a long appendage that turned out to be the animal’s tail. For many decades, we knew the things existed, but had all sorts of erroneous ideas about how they lived, and even how they looked when standing upright. T-Rex specimines were typically posed like tail-dragging mutant kangaroos.

It was at around the same time as they fixed the proper head on the Bronto, when I was in my first year of university, that a radical new theory was advanced that purported to explain the greatest mystery of the Dinosaurs, their utter mass extinction, which occurred in what was, geologically speaking, apparently the wink of an eye. The story behind this is one of the most magical examples of serendipity in the annals of science, and I hope I won’t bore the reader by recounting it here.

It’s strange now to reflect that as recently as the late 1970s there were lots of theories, but no compelling evidence pointing to a solution to the mass extinction of the Dinosaurs. It had clearly been a rapid and hugely traumatic event. As you dig upwards through the ancient strata, the creatures simply come to an abrupt halt, just beneath a geological marker known as the “KT” Boundary, a thin strip of sediment laid down between the end of the Cretaceous period and the beginning of the Tertiary. It was deposited about 65-66 million years ago, and no Dinosaur fossil has ever been found anywhere in the world that lies above the KT Boundary. This is fascinating to those of a certain bent, because it’s so definitive and distinct, a clearly visible layer of clay-like substance, which you can find all over the world; if you dug deep enough into your own back yard you’d hit the KT Boundary. Since it’s such a neat line drawn by nature, as if to serve as a tombstone marking the end of the Dinosaurs, scientists have always been curious about it.

One question that vexed  paleontologists related to the span of time the clay layer represented – sediments settle all over the Earth at a slow rate, creating strata over time like a sort of geological layer cake, and it isn’t easy to be precise about how long a particular band of sediment took to be laid down. It’s an educated guess. It was of keen interest whether the KT boundary took a hundred years to lay down, or a thousand, as the speed of its deposit might provide a clue as to the mechanism by which the Dinos went extinct. Rapid sedimentation might indicate some big event, perhaps major volcanic eruptions throwing huge quantities of ash into the air, or maybe some other weird occurrence. Who knew? Moreover, the time span of the sedimentation, if only it could be specified, was important not just to understanding what happened to the Dinosaurs, but to the science of evolution generally, since not only are there no Dinos above it, there’s also almost nothing within it, either, no large animals at all – it marks a lull in the history of life on Earth. How long was the natural world on pause?

A geologist named Walter Alvarez was one of the scientists curious about this, and he happened to have a father, Luis Alvarez, who was a Nobel prize-winning physicist. Scientists of different disciplines often ignore each other, but these two ate dinner together, so almost on a whim, young Alvarez asked his Dad if there was any way he knew to determine exactly how long it took any given sedimentary layer to deposit on the Earth’s surface. To his surprise, Pops said sure there was, and it was easy, actually. We know that heavy metals, the products of exploding stars (see prior blog!), rain down on the Earth from the cosmos at a more or less constant rate, and we know what that rate is. It would have been the same rate 66 million years ago, a fairly short interval in the life of a 14 billion-year-old Universe. All you have to do is pick an exotic metal like, say, Iridium, a relative of Platinum, something easy to find and measure, and the amount in the clay layer will indicate how long it had taken to accumulate, in much the same way that the depth of a snowfall could tell us how long it took to deposit, if snow always fell at the same steady rate.

Beautiful! So they measured the Iridium in the KT layer, and – hey, whoa – something was wonky. There was so much Iridium that by the ordinary rate of deposit, it would have taken longer than the age of the Earth itself to lay down. Huh? Repeated tests confirmed the result. The KT Boundary was unreasonably chock-full of Iridium. This was an utter mystery. So the elder Alvarez asked himself: apart from the ordinary dusting of the stuff that falls gradually from space, is there any other source of Iridium up there that could have wound up down here?

Why, yes, actually. Asteroids are full of heavy metals, so much so that if you could mine an asteroid you’d get rich, and…wait…did an asteroid hit the Earth!? If so, it must have been a big one, there was that much Iridium, and if an asteroid that big, say the size of Mt. Everest, hit the Earth, what would happen? You’d get a chain reaction. It would pierce the Earth’s crust, throwing up enormous amounts of debris and lava; balls of red hot lava would be thrown into ballistic sub-orbital trajectories that would land all over the world; everything, everywhere, would be set on fire; the smoke and ash, combined with the dust from the impact, would blot out the sun; photosynthesis would stop; plants would die; animals that ate plants would die; predators that ate those herbivorous animals would die; and – oh! – the Dinosaurs would go extinct!

Subsequent investigation found all manner of evidence in support of the theory, and it’s now generally (though not universally) thought that an impact event was the likely cause of the Cretaceous extinction. We even know now where the impact occurred – there’s a massive crater, itself buried in sediment, that takes in Mexico’s Yucatan Peninsula and a huge portion of the ocean offshore, and knowing the structure and chemical composition of the Earth’s crust as it was there, we can verifiably find bits of the Yucatan’s strata blown as far away as Alberta.

When I was born, we had no idea. By the time I was standing there looking at Sue’s arm, we did, and I thought about that as I tried to come to grips with what it all meant about me, and the fate of my own species. About 65 million years ago, if the theory is right, Sue’s descendants and every other Dinosaur in the Western Hemisphere would have looked up to see a burning mountain plunging from the sky, which might have glowed brightly enough to be literally blinding. At that moment many, perhaps most, of the complex creatures on the planet would have had just a few minutes, hours maybe, to live. The rest, with some puzzling exceptions, were doomed to starvation. By the time the ecosystem settled down again, and normal evolution resumed, there was nothing much around but variants of a few rather un-promising little critters, some of which looked a bit like a modern tree shrew, upon which to build the whole mammal lineage. Yet over a span of 65 million years, the shrews and their kin led to horses, whales, and finally you and me, and after all that, we primates ended up swinging under tree limbs using a close approximation of Sue’s arms. How Darwin would have loved to know that history, how we’d sussed out the speed at which evolution can take off from a modest start, and how eloquently the fossil record confirms his conclusion that all life is related.

Looking at the diversity of living things, we tend to think of nature as a great innovator, but really, it isn’t. At the same time as the fossil arm was fairly yelling in my ear about the ephemeral existence of all species, including, per force, my own, Sue’s forelimb was whispering this more subtle message: you, primate, are not so different from me. The superficials of different species change greatly, but the underlying stuff of all life is the same, and if you go back far enough you’ll find a common ancestor to all living things. As evolution waxes and wanes, it even repeats some of the same experiments, and produces creatures that are as different as they can be, yet look almost exactly the same – there were aquatic reptiles, Ichthyosaurs, swimming in the oceans over 100 million years ago that looked very like modern dolphins. We’re all made of the same raw material, and are pliable over time in the same ways, reacting to the same external conditions. Thus nature ends up playing infinite but similar tunes on the same fiddle. Sue’s claws, for example, were made of the same stuff as birds’ feathers, and your hair and fingernails too: keratin. A beetle is just a lobster that learned how to breath out of water, and its stiff exterior is made of the same stuff that holds crustaceans together: chitin.  It always works that way.

Recent advances in the study of DNA have given us tools that Darwin could never have imagined, and everything we find in the various genomes we unravel provides ever greater evidence that he was right. We are all assembled from sets of instructions that are astonishingly similar, just combinations of four amino acids, guanine, adenine, thiamine and cytosine, juggled about in different sequences, but not so much as you’d think. Your genome has a 99%+ commonality with chimpanzees, which may not seem so odd, but you also boast about a 60% commonality with a banana. Huge differences result from changes in the code sequences, of course, but it’s all the same code, because we’re all related. This makes some rather counter-intuitive facets of the natural world much easier to comprehend. When I was a kid, for example, my Dad was always puzzled by how substances derived from plants could have a medicinal effect on human beings. Why should a plant called Foxglove produce something that could lessen the severity of a heart attack? How did an extract of Willow bark, of all things, soothe a headache? Well, the answer is simple: we have much more in common with a tree than you’d think. Even you, an upright Great Ape, and a willow tree, surely as far removed from a mammal as any large and complex organism could be, have a common ancestor. Just like Darwin told us. Your genes prove it.

It’s amazing to me, and crushingly disheartening, that here in 2018 there are still those who doubt it, to the point that some school systems in America insist on teaching evolution as just one possible explanation for the subtle diversity of life on Earth, maybe not even an evidence-based explanation, and possibly less credible than the Bible story of creation. Over 90 years after the Scopes “Monkey Trial”, there are still evangelicals who’ll tell you with complete confidence that Dinosaurs and humans once walked the Earth together, and we don’t see the giant reptiles any more because they all drowned in the Flood after failing to make the cut for a limited supply of paddocks on Noah’s Ark (look, would you have wanted to give room and board to a T-Rex?).

I’m taken aback not so much by how they ignore both common sense and mountains of easily verified scientific findings, but why. What good does it do them? What fears and doubts are soothed, what hopeful expectations fulfilled, and what exalted view of Creation results? Theirs is actually an impoverished conception of the Cosmos, nowhere near as fantastic and enthralling as the one Darwin first explained, and no more compatible with a certain conception of God, either. Deism, an offshoot of Christianity popular in some quarters during the Enlightenment (Jefferson, among other luminaries, was an adherent) held, essentially, that God was the sum total of all the natural laws of the Universe. Evolution, to a Deist, would just be one strand in the rich tapestry of cosmic rules that formed the very essence of the Divine. Darwin himself, certainly, saw nothing in his theory that was necessarily incompatible with some concept of a Supreme Being. Look, here’s his sublime concluding sentence to On the Origin of Species:

There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Neither the Bible nor any other holy text has anything to offer that’s as awesome and inspiring as that. There is grandeur in this view of life. Perhaps you’ll get a better feel for Darwin’s beautiful prose if you hear it instead of read it. I can think of nobody better to make an audiobook of Darwin’s masterpiece than the great British naturalist David Attenborough, in whose direction I recently vented some mock rage, owing to his unflinching documentary depiction of nature’s gruesome realities:

If this was the foundational belief of some religion, I’d be there every Sabbath, singing Hallelujah.