TED日本語 - ケネス・ラコバラ: 恐竜の化石探しを通して知った、宇宙における人類

How do you find a dinosaur? Sounds impossible, doesn't it? It's not. And the answer relies on a formula that all paleontologists use. And I'm going to tell you the secret.

First, find rocks of the right age. Second, those rocks must be sedimentary rocks. And third, layers of those rocks must be naturally exposed. That's it. Find those three things and get yourself on the ground, chances are good that you will find fossils.

Now let me break down this formula. Organisms exist only during certain geological intervals. So you have to find rocks of the right age, depending on what your interests are. If you want to find trilobites, you have to find the really, really old rocks of the Paleozoic -- rocks between a half a billion and a quarter-billion years old. Now, if you want to find dinosaurs, don't look in the Paleozoic, you won't find them. They hadn't evolved yet. You have to find the younger rocks of the Mesozoic, and in the case of dinosaurs, between 235 and 66 million years ago.

Now, it's fairly easy to find rocks of the right age at this point, because the Earth is, to a coarse degree, geologically mapped. This is hard-won information. The annals of Earth history are written in rocks,one chapter upon the next, such that the oldest pages are on bottom and the youngest on top.

Now, were it quite that easy, geologists would rejoice. It's not. The library of Earth is an old one. It has no librarian to impose order. Operating over vast swaths of time, myriad geological processes offer every possible insult to the rocks of ages. Most pages are destroyed soon after being written. Some pages are overwritten, creating difficult-to-decipher palimpsests of long-gone landscapes. Pages that do find sanctuary under the advancing sands of time are never truly safe. Unlike the Moon -- our dead, rocky companion -- the Earth is alive, pulsing with creative and destructive forces that power its geological metabolism. Lunar rocks brought back by the Apollo astronauts all date back to about the age of the Solar System. Moon rocks are forever. Earth rocks, on the other hand, face the perils of a living lithosphere. All will suffer ruination, through some combination of mutilation, compression, folding, tearing, scorching and baking.

Thus, the volumes of Earth history are incomplete and disheveled. The library is vast and magnificent -- but decrepit. And it was this tattered complexity in the rock record that obscured its meaning until relatively recently. Nature provided no card catalog for geologists -- this would have to be invented. Five thousand years after the Sumerians learned to record their thoughts on clay tablets, the Earth's volumes remained inscrutable to humans. We were geologically illiterate, unaware of the antiquity of our own planet and ignorant of our connection to deep time.

It wasn't until the turn of the 19th century that our blinders were removed, first, with the publication of James Hutton's "Theory of the Earth," in which he told us that the Earth reveals no vestige of a beginning and no prospect of an end; and then, with the printing of William Smith's map of Britain, the first country-scale geological map, giving us for the first time predictive insight into where certain types of rocks might occur. After that, you could say things like, "If we go over there, we should be in the Jurassic," or, "If we go up over that hill, we should find the Cretaceous."

So now, if you want to find trilobites, get yourself a good geological map and go to the rocks of the Paleozoic. If you want to find dinosaurs like I do, find the rocks of Mesozoic and go there. Now of course, you can only make a fossil in a sedimentary rock, a rock made by sand and mud. You can't have a fossil in an igneous rock formed by magma, like a granite, or in a metamorphic rock that's been heated and squeezed. And you have to get yourself in a desert. It's not that dinosaurs particularly lived in deserts; they lived on every land mass and in every imaginable environment. It's that you need to go to a place that's a desert today, a place that doesn't have too many plants covering up the rocks, and a place where erosion is always exposing new bones at the surface. So find those three things: rocks of the right age, that are sedimentary rocks, in a desert, and get yourself on the ground, and you literally walk until you see a bone sticking out of the rock.

Here's a picture that I took in Southern Patagonia. Every pebble that you see on the ground there is a piece of dinosaur bone. So when you're in that right situation, it's not a question of whether you'll find fossils or not; you're going to find fossils. The question is: Will you find something that is scientifically significant? And to help with that, I'm going to add a fourth part to our formula, which is this: get as far away from other paleontologists as possible.

(Laughter)

It's not that I don't like other paleontologists. When you go to a place that's relatively unexplored, you have a much better chance of not only finding fossils but of finding something that's new to science. So that's my formula for finding dinosaurs, and I've applied it all around the world.

In the austral summer of 2004, I went to the bottom of South America, to the bottom of Patagonia, Argentina, to prospect for dinosaurs: a place that had terrestrial sedimentary rocks of the right age, in a desert, a place that had been barely visited by paleontologists. And we found this. This is a femur, a thigh bone, of a giant, plant-eating dinosaur. That bone is 2.2 meters across. That's over seven feet long.

Now, unfortunately, that bone was isolated. We dug and dug and dug, and there wasn't another bone around. But it made us hungry to go back the next year for more. And on the first day of that next field season, I found this: another two-meter femur, only this time not isolated, this time associated with 145 other bones of a giant plant eater. And after three more hard, really brutal field seasons, the quarry came to look like this. And there you see the tail of that great beast wrapping around me. The giant that lay in this grave, the new species of dinosaur, we would eventually call "Dreadnoughtus schrani." Dreadnoughtus was 85 feet from snout to tail. It stood two-and-a-half stories at the shoulder, and all fleshed out in life, it weighed 65 tons. People ask me sometimes, "Was Dreadnoughtus bigger than a T. rex?" That's the mass of eight or nine T. rex.

Now,one of the really cool things about being a paleontologist is when you find a new species, you get to name it. And I've always thought it a shame that these giant, plant-eating dinosaurs are too often portrayed as passive, lumbering platters of meat on the landscape.

(Laughter)

They're not. Big herbivores can be surly, and they can be territorial -- you do not want to mess with a hippo or a rhino or a water buffalo. The bison in Yellowstone injure far more people than do the grizzly bears. So can you imagine a big bull, 65-ton Dreadnoughtus in the breeding season, defending a territory? That animal would have been incredibly dangerous, a menace to all around, and itself would have had nothing to fear. And thus the name, "Dreadnoughtus," or, "fears nothing."

Now, to grow so large, an animal like Dreadnoughtus would've had to have been a model of efficiency. That long neck and long tail help it radiate heat into the environment, passively controlling its temperature. And that long neck also serves as a super-efficient feeding mechanism. Dreadnoughtus could stand in one place and with that neck clear out a huge envelope of vegetation, taking in tens of thousands of calories while expending very few. And these animals evolved a bulldog-like wide-gait stance, giving them immense stability, because when you're 65 tons, when you're literally as big as a house, the penalty for falling over is death. Yeah, these animals are big and tough, but they won't take a blow like that. Dreadnoughtus falls over, ribs break and pierce lungs. Organs burst. If you're a big 65-ton Dreadnoughtus, you don't get to fall down in life -- even once.

Now, after this particular Dreadnoughtus carcass was buried and de-fleshed by a multitude of bacteria, worms and insects, its bones underwent a brief metamorphosis, exchanging molecules with the groundwater and becoming more and more like the entombing rock. As layer upon layer of sediment accumulated, pressure from all sides weighed in like a stony glove whose firm and enduring grip held each bone in a stabilizing embrace.

And then came the long ... nothing. Epoch after epoch of sameness, nonevents without number. All the while, the skeleton lay everlasting and unchanging in perfect equilibrium within its rocky grave. Meanwhile, Earth history unfolded above. The dinosaurs would reign for another 12 million years before their hegemony was snuffed out in a fiery apocalypse. The continents drifted. The mammals rose. The Ice Age came.

And then, in East Africa, an unpromising species of ape evolved the odd trick of sentient thought. These brainy primates were not particularly fast or strong. But they excelled at covering ground, and in a remarkable diaspora surpassing even the dinosaurs' record of territorial conquest, they dispersed across the planet, ravishing every ecosystem they encountered, along the way, inventing culture and metalworking and painting and dance and music and science and rocket ships that would eventually take 12 particularly excellent apes to the surface of the Moon.

With seven billion peripatetic Homo sapiens on the planet, it was perhaps inevitable that one of them would eventually trod on the grave of the magnificent titan buried beneath the badlands of Southern Patagonia. I was that ape. And standing there, alone in the desert, it was not lost on me that the chance of any one individual entering the fossil record is vanishingly small. But the Earth is very, very old. And over vast tracts of time, the improbable becomes the probable. That's the magic of the geological record. Thus, multitudinous creatures living and dying on an old planet leave behind immense numbers of fossils, each one a small miracle, but collectively, inevitable.

Sixty-six million years ago, an asteroid hits the Earth and wipes out the dinosaurs. This easily might not have been. But we only get one history, and it's the one that we have. But this particular reality was not inevitable. The tiniest perturbation of that asteroid far from Earth would have caused it to miss our planet by a wide margin. The pivotal, calamitous day during which the dinosaurs were wiped out, setting the stage for the modern world as we know it didn't have to be. It could've just been another day -- a Thursday, perhaps -- among the 63 billion days already enjoyed by the dinosaurs. But over geological time, improbable, nearly impossible events do occur. Along the path from our wormy, Cambrian ancestors to primates dressed in suits, innumerable forks in the road led us to this very particular reality. The bones of Dreadnoughtus lay underground for 77 million years. Who could have imagined that a single species of shrew-like mammal living in the cracks of the dinosaur world would evolve into sentient beings capable of characterizing and understanding the very dinosaurs they must have dreaded?

I once stood at the head of the Missouri River and bestraddled it. There, it's nothing more than a gurgle of water that issues forth from beneath a rock in a boulder in a pasture, high in the Bitterroot Mountains. The stream next to it runs a few hundred yards and ends in a small pond. Those two streams -- they look identical. But one is an anonymous trickle of water, and the other is the Missouri River. Now go down to the mouth of the Missouri, near St. Louis, and it's pretty obvious that that river is a big deal. But go up into the Bitterroots and look at the Missouri, and human prospection does not allow us to see it as anything special. Now go back to the Cretaceous Period and look at our tiny, fuzzball ancestors. You would never guess that they would amount to anything special, and they probably wouldn't have, were it not for that pesky asteroid.

Now, make a thousand more worlds and a thousand more solar systems and let them run. You will never get the same result. No doubt, those worlds would be both amazing and amazingly improbable, but they would not be our world and they would not have our history. There are an infinite number of histories that we could've had. We only get one, and wow, did we ever get a good one. Dinosaurs like Dreadnoughtus were real. Sea monsters like the mosasaur were real. Dragonflies with the wingspan of an eagle and pill bugs the length of a car really existed.

Why study the ancient past? Because it gives us perspective and humility. The dinosaurs died in the world's fifth mass extinction, snuffed out in a cosmic accident through no fault of their own. They didn't see it coming, and they didn't have a choice. We, on the other hand, do have a choice. And the nature of the fossil record tells us that our place on this planet is both precarious and potentially fleeting. Right now, our species is propagating an environmental disaster of geological proportions that is so broad and so severe, it can rightly be called the sixth extinction. Only unlike the dinosaurs, we can see it coming. And unlike the dinosaurs, we can do something about it. That choice is ours.

Thank you.

(Applause)