How did you date the rocks in the mountain?
The limestone around the medieval city of Gubbio in Italy contains single-celled organisms called Foraminifera, or forams. These are microfossils of little, single-celled organisms that floated in surface water. Whenever a new foram species evolved, it would instantaneously spread all over the oceans and be captured in the sediment before it turned into rock.
When you say “instantaneously,” you are talking about long stretches of time compared with the human life span, right
Yes. If it took a thousand years to spread, in geologic time that is an instant. For the second half of the Cretaceous [the heyday of the dinosaurs] and all of the Cenozoic [the current epoch]—basically for the last 100 million years—forams have been the best thing we have for dating rocks. By the beginning of the 20th century, micropaleontologists were naming the genera and species of forams. They worked out their evolutionary family tree and linked different species to different parts of the standard geologic timescale.
You have a rock sample here in your office—what can it tell us?
Down here you can see some specks with your naked eye—those are foram fossils. Up here you can’t see them unless you have a microscope. The forams are almost gone, and that clear part of the rock represents the near mass extinction of forams and other species. Then farther up you can see the forams again.
That part, where the forams disappear, now seems to represent the time just after an asteroid hit the earth. Do you ever marvel at how much that single, chance event changed things?
The impact of a large object is something that could much more easily not have happened. Its chance of hitting the earth was just vanishingly small.
What if that asteroid had not hit the earth?
The descendants of those forams would have kept right on going, and with them the dinosaurs. The dinosaurs had been around for 150 million years, and they were the dominant large animals on the earth. The mammals were never going to displace them—until that impact took place and the dinosaurs became extinct. And you can see in the paleontological record that from that point on, the mammals burst forth, getting big, getting varied, taking over. We didn’t do it because we were superior organisms. We did it because the contingency—the unlikely event of the asteroid hit—got rid of the competition. One of the most profound things that I’ve learned about history is the importance of the contingency. That’s fundamental at the level of every one of us: What are the chances that a man from a little village in Kenya would meet a woman from Kansas and that they would have a child? The chance of Obama ever being born was vanishingly small.
You’ve been influenced by Yale historian John Lewis Gaddis. How does his work relate to yours—especially to your notion of contingencies and continuities?
Gaddis uses analogies from geology to explain history, and he’s written the most profound thing I’ve ever seen written about the present, past, and future. He says, “I prefer to think of the present as a singularity...through which the future has got to pass in order to become the past. The present achieves this by locking into place relationships between continuities and contingencies. On the future side of the singularity, these are fluid, decoupled, and therefore indeterminate. However, as they pass through it they fuse and cannot then be separated.” The important point is that a continuity is a historical trajectory in which, if you know what happened yesterday, you have a pretty good idea what’s going to happen tomorrow. A contingency is an event that was completely unpredictable and utterly changes everything?...
...like the asteroid that killed the dinosaurs. It was your interest in the contingency that thrust you into your latest passion, big history. What exactly does big history encompass?
The history of everything that we can possibly observe, starting with the Big Bang. Big history puts the history of the cosmos, the history of the earth, the history of life, and the history of humanity together into a single narrative.
Where did the notion of big history come from?
David Christian invented the concept. He’s a Russian historian who trained at Oxford and taught at Macquarie University in Sydney, Australia. He was at a meeting discussing the best curriculum for teaching history. Well, you should definitely start with Greece and the Near East, some people said. But then you would be leaving out Sumeria and ancient Egypt, so we should start there with the Middle East, said others. And somebody said there were all of these little towns in the Neolithic. Somebody else said, yeah, but that develops out of the Stone Age and the Old Stone Age. And then David timidly lifted up his hand and said, you know, if you have this line of reasoning, I can’t see any natural time to begin our history course more recently than the Big Bang. There was dead silence, and then one of his colleagues said, well, do you want to teach that? David swallowed hard and said, yeah, I think I do. Being a historian, he didn’t know about geology and paleontology and astronomy, so he got colleagues to come in and give guest lectures. Every now and then, one of the guest lecturers would say, I can’t do it this year, I am going to be on leave. And David would say, I think I can lecture on that topic, so he gradually turned himself into the first “big historian” and invented the term.
Your colleague Fred Spier has a different take on big history.
He likes to use a vague word, regime. One example of a regime is a time interval in history, like the Stone Age or the Renaissance or World War II. A regime can also be related to a place that’s a time interval but also unique to a particular part of the world—medieval Christianity would be a case. For me, the four great regimes of big history are cosmos, earth, life, and humanity.
What are the fundamental questions of big history?
What changes when a new regime comes into being? Cosmic history doesn’t end when earth history begins. David Christian says we are really talking about the gradual increase of complexity. For instance, you need hydrogen and helium for star formation, but the earth doesn’t function on hydrogen and helium. The earth is made primarily of heavier elements: magnesium, iron, silicon, and oxygen. That’s why you couldn’t get rocky planets in the early cosmos. You needed stars to grow until they exploded as supernovas, processing the material of the cosmos into those heavier elements, leading to more stars and more supernovas and more heavy elements and planets and then, with the emergence of carbon chemistry, life itself.
What are the most extreme contingencies that have altered the course of life on the earth?
One was the evolution of photosynthesis in microbes, the ability to convert sunlight into energy, giving off oxygen. The oxygenation of the earth’s atmosphere was the first and surely the greatest of all the episodes of air pollution that have ever been. Microorganisms that previously had free reign over the surface of the earth were forced into restricted environments like the bottoms of swamps and the insides of our stomachs. Another was the evolution by worm-like organisms of the ability to dig around through sediment. Before that, any dead organic matter that fell to the bottom of the sea and got covered by even a little bit of sediment was out of play. We’re talking about hundreds of millions or billions of years before that carbon could get back into the life cycle again. Once these organisms could dig, they kept all that carbon in play, speeding the whole biological cycle.
In his book Maps of Time, Christian compares the narrative of big history to a creation myth. Do you agree?
That’s a good way of thinking about it. People who don’t follow science have no idea of the richness of the stories that are coming out of it. It is so phenomenally complicated that no human being can ever learn or comprehend it all. David has said that the first chronological revolution was when people realized that they could go beyond memory. You can get some of the past by asking your parents what happened. Historians realized you could read and date old documents, finding out things that happened hundreds or thousands of years ago that nobody can remember. But it’s only in the last couple of hundred years, since Steno and the first geologists and paleontologists figured out how to read the history of the earth, and only in the last 50 years, since cosmologists figured out how to investigate the history of the cosmos, that we have seen David’s second chronological revolution start to unfold.
This is a major problem that standard historians have with big history: How can you take the big view and see the details at the same time?
Hey, we can go deeper and deeper and get more and more inside, but as we do so, it all becomes narrower. Historians have good reasons for being suspicious of big-picture things because early attempts did not work out too well. There wasn’t enough information to do it right, and it led to ideological conclusions like social Darwinism. Historians tend to be suspicious of anything that would be called a grand narrative, yet even some of them have recently made an effort in a field called world history, starting with the beginning of writing or agriculture or even anatomically modern humans. For some historians, history means written human history. They feel that scientists may be looking at the past but that whatever they are doing, it is something other than history.
So does big history suggest a grand, unified theory of everything like the kind that physicists are searching for?
Physicists like to speak of their goal to discover the theory of everything, but I think they’re on the wrong track. At least they’ve got the wrong name because for them the theory of everything is the theory of all laws and processes. The processes are not nearly as interesting as what unfolds through time as all of those processes operate, and that’s history. Big history is the theory of everything. What the physicist is talking about is not the theory of everything but the theory of how everything works. Physicists may put themselves out of a job when they get their theory of everything, but they won’t put the rest of us scientists out of work.