The Universe Within: Discovering the Common History of Rocks, Planets, and People

by Neil Shubin

  Removing the noise from the data is a tricky business. Let’s compare hypothetical fossil species and ask a simple question: Which one was more abundant in the distant past? Start with the obvious. Count every fossil of those species ever collected in every museum, and draw the simple conclusion that the most abundant species in the past is the one that has the most fossils in the museum collections. But we’d quickly realize the big problem: some fossils are common because they preserve easily. Or they may be easier to find. Still others are common because collectors liked them disproportionately; maybe they were relevant to a particular project somebody was doing. If you were to look at our collection from the Arctic, it is heavily weighted toward teeth and the back ends of jaws. Does this mean that teeth and jaws were more common than the rest of the animal? Of course not. It only means that they preserve and are found more easily than other parts. Dave Jablonski and his colleagues spend a lot of their time trying to remove these biases and noise from the fossil record to find the real signal—the census of life on our planet over time.

  Clams, oysters, mussels, and their relatives are not only features of the dinner table but also one of the most abundant components of the world’s fossil record. Common in ancient lakes, streams, and oceans, bivalve species fill cabinet after cabinet in paleontological collections worldwide. Their wide distribution in the fossil record (they have been on the planet for over 500 million years) makes them an ideal laboratory to test theories on how species diversity changes through time.

  To see things Dave’s way, you need to think about the 3.5-billion-year history of life as one big survival game, where the creatures that live longest and produce the most fertile offspring win. Then think about the features that help species survive and reproduce. For animals, you’d likely make a list that includes traits like the abilities to run faster than predators, to jump high, to climb efficiently, and to have jaws specialized for particular foods. It might mean being big at some times and small at others. You could measure how well creatures do certain activities, such as feed, reproduce, and move about. You could use these measurements to make predictions of winners and losers: faster animals would out-survive slower ones, faster breeders would do the same to slower ones, and so on. And for large chunks of geological time, tens or hundreds of millions of years, these features would seem to relate to the success of different species. Then you’d look to see how these features help animals at the biggest catastrophes in the history of life. You’d guess these features would be keys to long-term success. And you’d be dead wrong.

  What is the holy grail of paleontologists, the feature that predicts success during cataclysm? In the immense history of Earth, on many continents, over billions of years, through extinctions caused by asteroids, sea level change, and volcanic eruption, there seem to be rules about what happens to living things during cataclysms. One trait—among all those that life has ever had—seems to give us the ability to predict whether a species is likely to live or die at a catastrophe. The best survival tip for a species is to be widely spread around the globe. Species that have individuals spread about, preferably on different continents, fare better than those that are found in only one spot.

  For millions of years, survival and reproduction depend on how well creatures feed, move about, reproduce, and so on. Then, every so often, a catastrophe happens, and those traits become virtually meaningless. What matters is the happenstance of where they live. Rare events wipe the slate clean and briefly change the rules of the game. The creatures that survive catastrophe aren’t always “better” at any ecological trick. If the ultimate victory is surviving a catastrophe, then the winners are those that are globally distributed.

  If creative destruction is good for economies, so too is it for the biosphere. Survivors of global calamities inherit a new Earth—a planet with fewer competitors. Imagine a game of king of the hill. A huge, mean playground bully sits at the top of the hill and, with the advantages of his elevation and size, simply owns it. Nothing you do can get you up there. What is the best gift you can be given in this game? Maybe some random event, perhaps his mom calling him home for dinner, leaving the hill open for you. With the bully gone, you can simply scamper up the hill and gain the advantage of elevation to use when others come up.

  The king-of-the-hill idea may also hold for species. If a successful species occupies some niche, perhaps lives in a particular zone of the ocean, others cannot easily occupy that ecological space. Now, if a cataclysm removes that ecological version of king of the hill, the survivors can occupy the prize position without so much as a fight.

  Each catastrophe leaves a line of survivors with a new Earth.

  From our perspective, as one species sitting on top of 3.5 billion years of life’s history, we ask: What has this meant for us?

  Most of our fossil hunts are spectacularly unsuccessful, and my work in the 1990s with Farish Jenkins in Africa was no exception. We spent a fruitless month looking for mammals in 200-million-year-old rocks in Namibia, and at the finale Farish wanted to boost morale by taking us up north on a safari. After a few days’ drive, we found ourselves in Etosha National Park, a vast desert along the border with Angola. The desert plain is dotted with small water holes that are magnets for life. Every day we’d haul out of bed at sunrise, park our cars next to a quiet water hole, and sit for hours, simply watching the panoply of life come and go. First the birds arrive. Then come the zebras and buffalo. A pack of hyenas might wander about. Everybody scatters as a lion circles, then, when things seem safe, the whole crew settles back to a normal rhythm of feeding and drinking.

  Here we were in a glorious world of large mammals and birds of all kinds, but my brain was still locked inside the patterns of rocks of 200 million years ago. At that time, reptiles of every imaginable description roamed Earth; mammals were tiny shrew-sized creatures, and birds were nonexistent. Daily life at the water hole contains the imprint of catastrophes millions of years ago. The water holes before that time were loaded with a different creature, a very successful one. Dinosaurs, large and small, plant eating and carnivorous, occupied these niches. Instead of elephants and large plant-eating mammals, in the Cretaceous there were herds of ceratopsians and hadrosaurs. In place of large lions, there were tyrannosaurs and other large dinosaurian and crocodilian carnivores. The dinosaurs and their cousins were the kings of the hill for eons until they got knocked out by catastrophe. Only then did the descendants of a little mouselike creature, with teeth as small as grains of sand—whom dinosaurs trampled under their feet—grow to become the new kings of the hill.

  CHAPTER EIGHT

  FEVERS AND CHILLS

  Arctic bush pilots are a special breed. Years of solo flying endow them with a crusty independence and deep familiarity with the landscape. After countless hours looking down on terrain, pilots’ eyes can discern patterns hidden from the rest of us. During one flight in 2002, our pilot suddenly pushed the plane into a steep dive and veered into a tight bank, a maneuver that dropped us from ten thousand feet to about two hundred over the water in a small fjord. While I was seeing my life flash before my eyes, he saw a school of fish and, being a fisherman in his spare time, wanted to get a closer view. Even if my eyes weren’t closed, there was no way I could have perceived swimming arctic char from such an altitude.

  During one chopper run in 1985, a pilot named Paul Tudge was shuttling supplies between distant camps on Canada’s Axel Heiberg Island and Eureka Sound, two of the North’s most spectacular places. When the air is clear and the ground free from snow, the colors and images are so sharp that tiny details can be visible miles in the distance. In this part of the Arctic, barren mountain ranges border gentle valleys. The enduring action of ice, wind, and intense cold sculpts the bedrock into a range of obelisks, sheer walls, and potholes that almost seem unnatural. The sensation of otherworldliness is magnified by the lack of large plants: there are no standing trees, shrubs, or even grass in this area.

  Scanning brown, gray, and re
d vistas below his chopper, Tudge noticed something odd on the bedrock floor. Wind had winnowed a depression, out of which poked objects that looked like tree stumps. Not believing that there are trees in the Arctic, let alone ones that grew out of rock, Tudge set the chopper down. Lying in wait for him were not only tree stumps but piles of branches, logs, and other tree parts jutting from the ground. He dutifully collected samples and shipped them to one of the Arctic’s leading fossil plant experts, James Basinger of the University of Saskatchewan. Basinger dropped everything and mounted an expedition as soon as money and permits could allow; of course, in the Arctic this process can take a year or more.

  Awaiting Basinger’s spade was an entire buried forest mummified in eroding rock. The cold dry air left fine anatomical details of the leaves and wood intact, including their original cellular structure. The wood of these trees even burns. There is a big difference between these logs and a Duraflame; the Arctic ones come from a forest over 40 million years old.

  The stumps that jut from this frozen landscape expose redwood trees that would have reached heights of 150 feet or more. In the past, this place was no barren wasteland; it was alive with plants much like Northern California is today. Of course, nowadays the tallest tree up north is a little willow that rises mere inches off the ground. It is almost as difficult to see Arctic willows from six feet as Tudge’s fossil forest from the air.

  Tudge saw exposed stumps (left) that contained beautifully preserved wood over 40 million years old (right). (Illustration Credit 8.1)

  About twenty years before Paul Tudge’s flight, the eminent paleontologist Edwin Colbert received a box in his office at the American Museum of Natural History in New York City. Sent by a famed geologist from the Ohio State University, it contained a sheet of official letterhead wrapped around an isolated bone the size of a human finger. The colleague had collected this fragment in the field and wanted Colbert’s expert opinion.

  From his many years on expedition to the American Southwest, Colbert was able to identify the bone in a split second: it had the distinctive texture and shape of a jaw from an ancient amphibian that lived over 200 million years ago. Looking somewhat like fat crocodiles, these creatures were widespread throughout the globe for a good chunk of geological time. But this ordinary-looking fragment was very special: it came from the Transantarctic Mountains, a range two hundred miles from the South Pole.

  Colbert was a longtime fossil hunter, and the sirens went off in his head. Opportunity knocked; here was a continent completely unexplored for fossils. Colbert wasted no time assembling a dream team of experts from the United States and South Africa, who from years of working on the rocks of this age had the eyes to find new fossils. If fossil bones were present in Antarctica, this was the team to find them.

  Almost from the moment their boots touched the Antarctic sandstones, Colbert and his team had a field day picking bones from the sides of barren hills, where fossils were virtually everywhere they looked. One creature had a body shaped like a medium-sized dog, only instead of a jaw like a carnivore it had a large birdlike beak. What stopped Colbert in his tracks was not this creature’s bizarrely chimeric form but something far more mundane: paleontologists had known of this creature for decades. In the 1930s, South African geologists identified an entire layer that contains thousands of them extending across a wide swath of the Karoo Desert. This so-called Lystrosaurus Zone even reaches South America, India, and Australia. Now, with a Lystrosaurus level in Antarctica, Colbert and his colleagues uncovered yet another clue exposing the reality of continental drift. With the match of the rocks, coastlines, and fossils, a new view of Antarctica emerged: the continent in the past sat as a keystone at the center of a vast supercontinent that included Africa, Australia, and India. This clump of continents covered much of the southern part of the planet.

  The pile of fossils that Colbert’s group discovered revealed another fact of Antarctica’s past. Lystrosaurus, like the amphibian that led him there in the first place, was a cold-blooded animal that could live only in warm tropical or subtropical climates; think big salamanders or lizards. Ditto the fossil plants. Colbert and his team labored near the center of a vast frozen continent, close to where Robert Falcon Scott and his party froze to death nearly sixty years before. But everything inside the rocks pointed to one conclusion: Antarctica was once a warm and wet world teeming with tropical life.

  Expeditions that followed Colbert’s only exposed more of Antarctica’s disconnect between its frozen desolate present and its lush past. The world that Colbert uncovered was followed by another filled with dinosaurs and their kin. In rocks even more recent, 40 million years old, this tropical continent was home to modern rain forests, amphibians, reptiles, birds, and a whole menagerie of mammals. For most of its history, Antarctica was a paradise for life.

  Then, starting 40 million years ago, the entire continent went into the freezer, and with it Antarctica witnessed the greatest and most complete extinction of any continent in the history of the planet. From a world rich in plants and animals, virtually every land-living creature simply disappeared.

  There is symmetry to Tudge’s flight near the North Pole and Colbert’s exploration of the South: one unveiled temperate forests, the other tropical animals in regions that today house frozen deserts. The story of the poles is that of the entire planet. Our present—with its polar ice—is an aberration. For most of history our planet was warm, almost tropical. If the rocks of the world are a lens, they reveal that our modern, relatively cold landscape is not the normal state of affairs for the planet.

  In this great cooling lies one of the major events that shaped our bodies, our world, and our ability to see all.

  TAKING OUR TEMPERATURE

  Carl Sagan once spoke of a paradox about our planet’s climate. The sun is not a constant beacon of light; it started its stellar life as a relatively dim star over 4.6 billion years ago and has increased in brightness ever since, being about 30 percent brighter and warmer now than when it formed. With such a dramatic increase in heat over the years, Earth should have been a frozen waste in the past and now be a roiling cauldron of molten crust. Yet all our thermometers for the planet paint a different picture. Glaciers exist today during an era when the temperatures should be downright hellish. There are signs of liquid water inside 3-billion-year-old rocks—at a time when Earth should have been a ball of ice. Sure, we’ve had our moments of hot and cold, but if you think about Venus’s surface temperatures of 900 degrees Fahrenheit and Mars’s of -81 degrees, Earth has been a stable Eden relative to its celestial neighbors. Somewhere on the planet lies a thermostat that buffers it from dramatic extremes in temperature.

  Inroads to the thermostat were discovered by a student who was as persistent as he was headstrong. He started his graduate career by loudly proclaiming to his thesis adviser that he had a brand-new theory of electrical conductivity. The response to this arrogant introduction was a simple “good-bye.” Perseverance paid off, and, probably to the relief of his teachers, in 1881 Svante Arrhenius moved to Stockholm to work with a professor at the Academy of Sciences there. After that gig, Arrhenius went on to think of other scientific problems.

  One scientific puzzle was right in front of Arrhenius’s eyes. He saw the factories of the Industrial Revolution belching coal smoke—in his words, “evaporating our coal mines into the air.” Arrhenius knew from previous work that carbon dioxide, a major constituent of the fumes, could capture heat. He made a few calculations that revealed how increased carbon dioxide in the air would trap heat on Earth and raise global temperatures. This idea was to lay fallow for a number of years, during which time Arrhenius won the Nobel Prize for work derived from the seemingly lackluster doctoral thesis that had so annoyed his professors.

  The famous greenhouse effect is based on Arrhenius’s work. The more carbon dioxide there is in the atmosphere, the more heat is trapped by the planet and the hotter things get. Of course the reverse is true. But there is a deeper meaning to
carbon in the air, one that emerges only when you take the long view on timescales that extend millions of years in the past.

  The television character Archie Bunker once famously said of beer, “You don’t own it, you rent it.” The same holds true for every atom inside us; we are the temporary holders of the materials that compose our bodies. Few of these constituents are more important to the balance of life and the planet than carbon. The connection among parts of Earth depends on how carbon moves through air, rock, water, and bodies. To see this chain of connections, we need to consider living things, rocks, and oceans not as entities in their own right but as stopping places for carbon as it marches along during our planet’s evolution.

  Viewed in this way, the amount of carbon in the air depends on a delicate balance of conditions. Carbon in the atmosphere mixes with water and rains down to the surface as a slightly acidic precipitation. We see the effects of this in our daily lives; in my university, built largely in the late nineteenth century, few gargoyles still have faces. Acid rain works on exposed rock everywhere—on mountainsides, rubble fields, and sea cliffs. Once the acid rain breaks down rocks, the water—now also enriched with carbon that was inside the rocks—eventually winds its way through streams and rivers into the oceans. At this point the carbon gets incorporated into the bodies and cells of the creatures that swim there: seashells, fish, and plankton. When sea creatures’ remains, loaded with carbon, settle to the bottom of the ocean, they ultimately become part of the seafloor. And, as we’ve known since Marie Tharp, Bruce Heezen, and Harry Hess, the seafloor moves, only to be recycled deep inside Earth.