When we begin to appreciate the idea of rocks as recorders of the truly ancient history of the Earth and start to learn what happened in that history, we experience a dizzying but exhilarating expansion of our appreciation of time. It’s like taking off in an airplane, rapidly climbing to cruising altitude, and suddenly seeing our narrow surroundings unfold into a vast and intricate landscape—in this case the landscape of history.
-Walter Alvarez, The Mountains of Saint Francis
It was one of those rare spring days when the wind blows hot and dry out of the hills. In 575 McCone, the blinds were lowered and the windows were cracked, but the classroom was still an oven and the students fanned themselves with a handout labeled “Overview of Human History on Five Time Scales.” The page showed five vertical timelines, each one differing in scale by an order of magnitude. The bar on the left represented two million years of history while the one on the far right represented a mere two centuries. The timelines integrated various data; for example, temperatures were plotted on the leftmost one—a jagged line of peaks and valleys as the paleoclimate jerked from hot to cold and back again—as well as the time spans of various species of the genus Homo (H. habilis, H. erectus, H. sapiens). As you moved to the shorter time scales, the climate data gave way to the familiar historical eras (Bronze Age, Roman Empire, Dark Ages, etc.). In the timeline at the far right were the names and life spans of individual human beings—six generations, all told, beginning with one José Fernandez, who lived in Spain through the Napoleonic and Carlist Wars, and ending with his descendant Walter Alvarez, born 1940 in Berkeley.
Walter Alvarez is best known as the geologist who, along with his father, the Nobel-winning physicist, Luis Alvarez, and a coterie of other scientists, including chemists and astronomers, solved the riddle of what happened to the dinosaurs. He is also the instructor of this course, which endeavors to treat all of time, from the Big Bang to the present, as a single unit of study. The title of the course is Big History: Cosmos, Earth, Life, Humanity. It was late in the semester and the class had finally made it to the part about them.
Despite the surname, Alvarez, who is tall and long-limbed, looks more Swede than Spaniard. At 68, his hair is growing sparse and silvery and his eyes are pale blue behind his spectacles. In his gray Dockers and long-sleeved shirt buttoned at the wrists, he was the only person in the room who seemed impervious to the heat. Upon arriving in class he made the rounds, exchanging greetings with some of the students, all of whom he appeared to know by first name. They, in turn, addressed him simply as Walter.
To begin, he quickly ran through the handout, urging the students to go back to it often. The only way to really internalize this material, he stressed, is to practice at it like the piano. He also encouraged them to fill out the last two columns according to their own historical interests and personal genealogies. It wasn’t about him, after all, it was about them making history relevant to their own lives. Before moving on, he directed their attention to a vaguely delineated period of time in the center timeline marked “Neolithic (Agriculture) Revolution.” This is the period of time, after the glaciers of the last ice age receded around 10,000 years ago, when humans learn to farm and the curtains begin to rise on civilization. Alvarez points out that human development corresponds to an abnormally stable climate. The question is whether that climatic stability was a precondition for civilization and, if so, what happens if that stability ends.
The main lecture topic for the day is not climate, however, but the domestication of fire. “I’m going to show you a miracle,” he announced with a smile. Turning off the lights, he struck a match and the students, now roused from their torpor, oohed and ahhed obligingly. “We take it for granted, but it took humanity tens of thousands of years to learn how to do that.” What’s more, it took millions of years for fire to develop, period; early Earth was hot, but there was no fire until the advent of bacteria, which created the oxygen, and plants, which provided the fuel. Fire, he said with a note of genuine awe, could be thought of as nature’s way of limiting oxygen levels, a way of taming photosynthesis!
From there, he transitioned into the myth of Prometheus, who angered Zeus by stealing fire from the gods and giving it to man. Taming fire, Alvarez said, was even more important to humanity than domesticating animals and plants. Fire let us move out of Africa. It let us cook and preserve food and clear land. It allowed us to make charcoal, which meant hotter fires, which led to pottery and metal work and to the Industrial Revolution, when we learned to turn fire and heat into motion, eventually propelling ourselves to the Moon. “And the absolutely definitive thing about fire,” he said reaching a sort of denouement, “is that it’s universal. There’s not a tribe or a culture that doesn’t use it, but no other species does.”
What is a geologist like Walter Alvarez doing teaching a history course? The argument could be made that history is what he has always taught—Earth history. Granted, that’s not what is generally meant by history, which as a traditional field of study falls squarely within the humanities and focuses almost entirely on written documents. But that kind of history only extends our knowledge of the past by a few thousand years, whereas the record written in the rocks delves billions of years—a span so profound it is sometimes called “deep time.” And geology is just a start; taken together, the historical sciences (such as archeology, geology, paleontology, astronomy, and cosmology) expand not only our conception of time but also space. How big is history? It turns out there’s an answer of sorts to that question. As the historian Cynthia Brown writes in a book entitled simply Big History:
The universe in which we whirl began as a single point 13.7 billion years ago; it has been expanding ever since, with its temperature steadily decreasing. Our universe has at least four dimensions, three of space and one of time. Just now the size of our observable universe is roughly 13.7 billion light-years on each of three dimensions by 13.7 billion years on the dimension of time, increasing as I write and you read.Reading big history is often like this; like listening to Eric Idle’s “Galaxy Song” in The Meaning of Life (“Just remember that you’re standing on a planet that’s evolving / And revolving at nine hundred miles an hour….”) And yet big historians, such as they are, insist the subject is both serious and valid, even if the scale of the project makes it difficult to get a handle on. Scale is, in fact, key to the whole enterprise. As David Christian, the Oxford-educated historian who gave big history its name, writes in the introduction to his book, Maps of Time, “No geographer would try to teach exclusively from street maps” yet most historians concentrate on some facet of history or other without ever considering the whole. Big history, he suggests, is an attempt to create a “temporal equivalent of a world map.” Cynthia Brown calls it history “with the lens zoomed open as wide as possible.”
Big history is still in its infancy. There is as yet no academic journal devoted to the field, no professional society to host conferences, not even a textbook to teach from (although one is reportedly forthcoming from McGraw-Hill). It has arisen now, in large part, because radiometry and other advanced dating techniques have made it possible to assign remarkably precise dates to distant events and to assemble a fairly accurate chronology of the deep past.
As with world history before it, however, the subject has its detractors, who criticize big history as too broad to offer any meaningful insights. In Maps of Time, Christian counters the charge. “Frames of any kind exclude more than they reveal,” he writes. “And this is particularly true of the conventional time frames of modern historiography, which normally extend from a few years to a few centuries. Perhaps the most astonishing thing the conventional frames hide is humanity itself.” Indeed, most of human history (more than 95 percent of it) is actually prehistory—something classical historians have not, as a rule, concerned themselves with.
When I asked Walter Alvarez what he most hoped his students would take away from his class, he reflected for a moment before answering, “Historical-mindedness.” By which he meant he wanted students to bring a level of historical curiosity to whatever they encountered in life.
Toward the beginning of every semester, Alvarez takes his students out onto the fifth floor balcony of McCone Hall where, on fogless days, there is an overview of the Bay and a direct line of sight to the Golden Gate. There, he and his students survey the topography, paying special attention to place names. There’s San Francisco, San Mateo, San Jose—those are all Spanish names. And there’s Alameda and Yerba Buena and Alcatraz; those are Spanish names too but the last one has roots in Arabic. “Alcatraz,” he explains, “means seabird. It’s a cognate with albatross.” Many Spanish and even English words that begin with “al” (for example, algebra) are of Arabic origin. So then he asks, “Why do you think there’s an island with an Arabic name in the middle of the Bay? And that’s historical-mindedness, because that leads you back through the whole of Spanish history to the Moorish conquest.”
Historical-mindedness may seem like an exceedingly modest goal for a class that, in the space of a single lecture, can segue from the Crab Supernova of 1054 to the Battle of Las Navas de Tolosa in 1212, with stops along the way to consider the scablands of Eastern Washington and the last deglaciation, all in service to a larger discussion about the nature of time. But rest assured, Alvarez has grander ambitions. In the long run, he says, he’d like to see big history become a scientific discipline. “If all big history ever is is a telling of the past with all of these things brought together,” he says, “it will be a wonderful subject for an undergraduate course but it won’t attract scholars and scientists to work on it.” What big history needs, he feels, is a set of really interesting, “research-grade” questions.
“One of the things you ask yourself is, ‘What do all of these regimes—let me use the word regime for cosmos, Earth, life, and humanity—what do these regimes have in common, and what’s different about them?’” For one thing, he said, they “use” different stuff: Cosmic history basically uses hydrogen and helium, whereas Earth history is more about elements like silicon and oxygen and magnesium, and life history uses carbon and hydrogen and nitrogen and phosphorus, etc. In that sense, they’re quite different. But they also have at least one thing in common; namely, that all the change that takes place in those regimes is driven by energy. “That leads you into questions of thermodynamics and how energy flows between one concentration and another. How does it do work in the process? How does it gradually leak away and get lost as heat? Another question is, ‘What’s the role of contingency and continuity in history?’ Continuity being where if you know what’s going on today you have a reasonably good idea what’s going on next year or a hundred years from now. And contingency being those absolutely unpredictable things that you couldn’t possibly know about, after which everything is different.”
Originally, this article was going to be a simple Q&A with Alvarez about his latest book, The Mountains of Saint Francis, a geologic journey through the Apeninne mountains of Italy. It was in those mountains—particularly in a limestone outcrop near Gubbio—that Alvarez first became interested in the question that would come to define his career: What happened to the dinosaurs?
In his office, Alvarez showed me a polished sample of stratified rock about the size of a deck of cards. The top part of the sample is made up of pink limestone. The lower part is white limestone. And in the middle is a thin dividing layer of clay. “So this is a piece of the Cretaceous-Tertiary boundary from Italy,” he said. “That’s the top bed of the Cretaceous, and if we took this across the hall and looked at it under the microscope, we’d see that it’s full of these fossilized single-celled marine organisms called forams. They go on down here for 40 or 50 million years. They’re always there.” He moved his finger up a tick, just above the line of clay, to the younger rock in the strata. “Here those guys are gone. Never to appear again.”
An enormous extinction occurred at that line, Alvarez explained. Not only did the tiny forams disappear but the dinosaurs and most other life forms did too. To determine how long it took the layer of clay (commonly referred to as the K-T boundary) to deposit, Luis Alvarez, Walter’s father, suggested testing it for traces of iridium, an element that is exceedingly rare on Earth, but more common in meteorites, which constantly shower the Earth with microscopic dustings of the stuff. If they found iridium in the clay, they reasoned, they could assume a long period of deposition. If they didn’t, it had formed more suddenly.
The Alvarezes enlisted two Berkeley chemists, Frank Asaro and Helen Michel, to analyze the sample. What they found surprised everyone. Not only was there iridium, there was way too much of it; three hundred times as much as in the layers above and below the clay. And the finding held true for K-T samples from other sites around the globe.
The iridium was a bit like DNA evidence in a criminal case, narrowing the possible culprits to something extraterrestrial. But what? After ruling out a supernova as the source, the Alvarezes hypothesized that an asteroid had struck the Earth, kicking up a global shroud of dust that blocked out the sun long enough to shut down photosynthesis and kill off the warm-adapted dinosaurs.
When they presented the theory in 1980, critics immediately attacked the findings, in what became one of the more acrimonious debates in the annals of science. The reaction was partly territorial; who were these outsiders to tell paleontologists their business? “The arrogance of these people is simply unbelievable,” paleontologist Robert Bakker said. “They know next to nothing about how real animals evolve, live, and become extinct. … The real reasons for the dinosaur extinctions have to do with temperature and sea level changes, the spread of diseases by migration, and other complex events. In effect, they’re saying this: We high-tech people have all the answers and you paleontologists are just primitive rockhounds.” Luis Alvarez, never one to mince words, more or less agreed. He told a Times reporter that paleontologists weren’t very good scientists. “They’re more like stamp collectors.” If he scorned his opponents, he said, it was because they were publishing “scientific nonsense.”
In his own accounts of the matter, Walter Alvarez habitually downplays the personal animosity in the debate. In his view, most of the resistance to the impact theory was cultural and derived from a long-established tenet among paleontologists and geologists called uniformitarianism, one formulation of which held that all earthly phenomena, from the carving of canyons to mass extinctions, could be explained by ongoing earthly processes over vast stretches of time. In this gradualistic worldview, globally catastrophic events were rejected a priori.
As it happened, the impact theory was vindicated after the 1990 discovery of a huge crater off the Yucatan peninsula, which carbon dating matched precisely to the Cretaceous-Tertiary boundary layer. If the iridium was the DNA in the case, the crater was like finding shell casings at the scene of the crime. Between the genetic evidence and the ballistics testing the case was—in most minds—closed.
Walter Alvarez doesn’t gloat in that victory. Reflecting on the outcome in his office, he said: “It was hard fought, as any of these things are. I’ve come to realize that major scientific advances don’t get made without major controversy and real argument. Which is the way it ought to be. But I was thinking about it recently. Somebody was asking me, ‘Why were people so resistant to plate tectonics or to the impact theory? Why didn’t they see the light?’ My thought about it was, ‘Eventually almost everybody did, but after a good strong argument.’ And just compare that with the way it is in politics or ideology. How often do you see somebody on the extreme left or extreme right change their mind and move to the other side on the basis of accumulated evidence? They don’t. So I think that the fact that scientists do is one of the great things about our kind of work.”
One could say that the Cretaceous-Tertiary impact is Walter Alvarez’s personal contribution to the landscape of history. The discovery not only altered the historical narrative, it also changed a mode of thinking that had put blinders on scientists’ conception of the past. More than anything, however, the impact theory is profound for what it says about us; that is, but for an astronomical fluke, the dinosaurs would probably still be here and we wouldn’t.
It’s precisely that kind of thing that Alvarez is getting at when he asks what the roles of continuity and contingency in history are. It’s a good question. Not research-grade perhaps, but good and deep. More like a koan—something to meditate on in the hopes of finding clarity.
After the semester ended, I asked Alvarez whether, having taught Big History for a third time, he still thought its prospects of becoming a scientific discipline were promising.
“I think it’s promising but difficult,” he answered. “It’s not clear to me whether there are going to be questions as compelling as the Cretaceous-Tertiary extinction question was.” And yet, he insisted, the uncertainty didn’t bother him; he’s happy in the search. “Most people, they want to know answers, right? Scientists want questions. And if you’ve got a really good question that nobody knows the answer to, then that’s where a scientist wants to be. But maybe there’s another level where you don’t even know what the questions are yet. And I kind of like that territory. If everybody knows what the question is and knows what kind of discovery needs to be made, then you just need the data. But if you’re interested in the possibility of discoveries no one’s ever even thought about before, then maybe it helps to be in a situation where you don’t even know what the question is.”
Then he laughed and asked, “Does this sound crazy?”