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A Geologial Perspective on Big History

Walter Alvarez


     Big History was invented and named around 1990 by the Anglo-Australian professor of Russian history, David Christian, who was curious to know what had happened before the Greeks, before the Egyptians, before the first agriculturalists and the hunter-gatherers—even before there were any human beings at all.  Thus he was led out of his familiar comfort zone of written history, into the historical sciences—archaeology, geology, paleontology, astronomy, and cosmology.  Through the 1990s, David Christian learned more and more science, until he was able to lecture on those topics himself, and to write his superb book about Big History, Maps of Time.1

     One of the first scholars to take up Christian's concept of Big History was the Dutch sociologist Fred Spier, whose thoughtful little book is a fine introduction to the subject.2  Spier proposed the usefully vague term "regime" to designate the various ways to divide up Big History, and I find myself thinking in terms of four major historical regimes—Cosmos, Earth, Life, and Humanity

     The concept of Big History is probably unfamiliar to most people, because it is a brand-new discipline.  It attempts to understand the broad trends and the general character—if not all the details—of everything that has ever happened in the past.  Big History aims to make sense of everything that has ever happened in the regimes of Cosmos, Earth, Life, and Humanity, or at least everything we have any possibility of knowing about.  It also aims to bring together, in fruitful conversation and collaboration, scholars and scientists from a very wide range of disciplines.  My own field is geology, so I start from an interest in Earth history, but other historical disciplines have always interested me.3  Big History has now given me the opportunity to see how the history of the Earth fits into the history of everything else.

     Not many people have even heard of Big History, and there are still fewer who have undertaken to give a course in it.  To my knowledge there are about dozen universities around the world with a course in Big History.4  I have been teaching a course called "Big History—Cosmos, Earth, Life, Humanity" at Berkeley for the last three years, and have found it the most exhilarating intellectual experience of my entire career.  This course appeals to the most intelligent, intellectually wide-ranging, and motivated of our students, from all years and every possible major, and I have immensely enjoyed them all.  I can strongly recommend this new discipline to teachers with broad interests and adventurous spirits.

     I think what I most want my students to acquire from the Big History course—in addition to a general outline of the history of Cosmos, Earth, Life, and Humanity—is something I have come to think of as "historical mindedness"—the habit of thinking historically about all the things we encounter in our lives—cities and buildings; mountain ranges, deserts and rivers; plants, animals and people; the night sky; languages; industries, governments, and churches; the food we eat; the bodies we are born with.  For me, historical mindedness—asking focused questions about the past—is the key to deeply understanding the world we live in.

     I remember, years ago, seeing a cartoon that really captured historical mindedness.  A couple of American tourists are standing on the Capitoline Hill in Rome, looking out over the Forum, with ancient ruins stretching all the way to the Colosseum.  And one of them is saying, "I imagine there must be a really interesting story behind all this!"

*          *          *

     If you are going to teach a course about all of history, you need some focus, and I've chosen to focus on Spain, in which I have a passionate interest because I come from an old Spanish California family.  It is clearly useful for California students to know something about Spanish history, for it has affected our State so strongly, but the real point is to inspire them to learn in depth about the history of whatever especially interests them.

     To get my students started in the habit of historical mindedness I take them up to the roof of our building for a view across San Francisco Bay, where we can see San José, Palo Alto, San Carlos, San Mateo, San Leandro, Alameda, El Cerrito, and the island of Yerba Buena. So many Spanish names!  But not surprising to my students, because they all know that California was a Spanish and Mexican colony before it was incorporated into the United States.

     Then I point out the famous prison island of Alcatraz.  Many of my students know, or can guess, that this is also a Spanish name, but few know that this one is different—that it was originally an Arabic word, meaning sea bird, and related to our word albatross.  What is an Arabic name doing out in the middle of San Francisco Bay?  Historical mindedness is the key to asking and answering and understanding questions like this.

     As my students think historically and dig back into the past to understand what this Arabic place name is doing out in the middle of San Francisco Bay, they come face to face with Mediaeval Spain, partly or almost entirely Islamic from 711 to 1492 ce, a time when a great number of Arabic words entered the Spanish language.  They discover that Islamic Córdoba was then the most civilized city in western Europe.  They learn how the taking of Moslem Toledo by King Alfonso VI of Castile in 1085 made possible the translation of the works of Aristotle from Arabic into Latin, triggering what has been called the Twelfth Century Renaissance in Western Europe.  And they wrestle with how to interpret those mediaeval Spanish centuries—were they primarily characterized by the crusading warfare of the Reconquista—the Reconquest—or by the Convivencia—the living together—of the three faiths—Islam, Judaism, and Christianity?  And that forces them to think about what kind of relations could be possible between those faiths during their own lifetimes.5

     As they carry their understanding from the Island of Alcatraz back through the Spanish Middle Ages, my students come to think about all the centuries that have passed, making our brief lifetimes seem almost trivial.  They are forced to confront the vastness of time, and it is a sobering confrontation.

     Pushing back historically beyond Mediaeval Spain into the Roman Empire that lies behind it, and on to Classical Greece, my students come to another sobering realization.  They discover that there was once a great civilization, during the Bronze Age, in the Eastern Mediterranean and the Near East, from roughly 2000 bce to 1200 bce—a glorious civilization which in places like Anatolia and Greece vanished completely.  No one knows for certain why, although the contending explanations include clustered earthquakes, or developments in warfare that may have let barbarian warriors defeat charioteers.6  Whatever killed Bronze-Age civilization, those cities and palaces disappeared so completely that Homer, writing three or four centuries later, knew only oral legends about the Bronze Age wars of Troy.  The total Dark Age that intervened dwarfed any darkness that happened after the fall of Rome.  Today the work of archaeologists has recovered Bronze Age history for us, but it is still unsettling to understand that an entire civilization can vanish without a trace into the abyss of time.

     Traveling back beyond the Bronze Age, we explore the domestication of plants and animals during the early development of agriculture, after the great ice sheets melted, and beyond that, the time of hunter-gatherers who slowly domesticated fire.7  It is like zooming out to see broader and broader panoramas of time as we travel back through the repeated glacial oscillations of the last million years.  As their minds zoom out, my students come to realize that although a million years is a colossal number of years, or of human lifetimes, one million years is the basic unit of time when geologists study the history of the Earth.  Learning to think like geologists, they realize that while written human history goes back about 5,000 years, Earth history goes back about 5,000 million years.

     Returning from the Near East to Spain, we meet the last known Neanderthals, 28,000 years ago, at Gibraltar, as if that were their last temporary refuge as Europe was overrun by our own ancestors.8   Zooming our view out to five million years, we can see the evolution of humans and our closest ancestors, mostly across the Strait of Gibraltar in Africa.9

*          *          *

     Right at five million years ago we come to a spectacular geological discovery—the drying up of the Mediterranean Sea by evaporation after mountain uplift blocked the inflow of Atlantic water between Spain and Morocco.  What a realm of desolation the Mediterranean must have been—a parched desert, two miles below sea level, stretching from Spain to Egypt!10  And what an incredible spectacle when some unsuspecting little stream, draining down into the Western end of the Mediterranean desert, finally breached the watershed and brought the Atlantic Ocean pouring down into the desert in what may have been the greatest waterfall in all of Earth history, eroding the Strait of Gibraltar.11

     Now my students are fully in the realm of Earth history, and they learn of episodes that are as intensely interesting as they are unfamiliar, and about how geologists read history written in rocks.12  They learn about the extremely slow collision between Spain and France that gradually pushed up the Pyrenees Mountains about fifty million years ago, creating a barrier that has played a critical role in European history.

     A little farther back, at sixty-five million years ago, there was a different kind of collision—this one blindingly fast—when an asteroid the size of Mount Everest, traveling at 70,000 miles per hour (thirty kilometers per second), crashed into Mexico.13  Debris from the impact traveled ballistically, outside the atmosphere, to every point on the Earth, and upon re-entering the atmosphere, generated frictional heat that set continent-scale wildfires.  The air all around the globe was midnight black from dust and smoke, while nitric acid rained out onto the dark and freezing land and sea.  When the air cleared, CO2 at twice-normal levels raised the temperature to scorching levels.  And when this environmental catastrophe was finally over, many species of plants and animals were gone forever, producing what we could think of as a paleontological Dark Age.  We mammals are the survivors who then built a new biological world.  We know of six great extinctions of life, but the cause of the other five is still a mystery.14

     As we continue to run our movie of Big History in reverse, watching the more usual, slow changes that characterize the history of Earth, we see the Atlantic Ocean closing back up, until at 150 million years ago Spain and Portugal are located adjacent to Newfoundland, as part of the supercontinent of Pangaea.15  As we zoom backward in time, Big History drives home the sobering realization of the abyss of time that separates us from the deep past. 

     And the story of continental drift continues on back, letting us see how Pangaea was assembled still earlier, from fragments of an even older supercontinent that geologists call Rodinia, dating back to around a thousand million years ago.16  The pageant of continental assembly and fragmentation has remarkable episodes—for example, at one point all the southern continents had been assembled into Gondwanaland, but Gondwanaland was upside down, with modern north pointing south.  Then Gondwanaland drifted down across the South Pole, coming up the other side with north now in the right orientation, and leaving a slow track of glacial deposits from one end of Africa to the other, marking the passage across the South Pole.17  Just imagine the confusion of the geologists who, in the days before continental drift was understood, discovered those Ordovician glacial deposits from about 450 million years ago, in the blazing hot, hyperarid center of the Sahara!

*          *          *

     The history of Life has always been the hardest part of Big History for me to teach, because the ever-multiplying branches in the tree of life render its history exceedingly vast and complicated18, and because to understand it you need to know a lot of unfamiliar names of geological periods, like the Ordovician.  Presenting the history of Life has proven to be a difficult task, but here is an idea for a way to do it:  In a Big History course about "Cosmos, Earth, Life, and Humanity," we are clearly following a historical trajectory that leads to humans, and are thinking about what has brought about our human world.  So why not think carefully about the history of the human body? 

     Each of us is born with a human body, with the various parts all tied together, making a well functioning unit.  But let's use our historical mindedness and think about how that body came to be—let's think about the evolution of humans.  Paleontologists can trace our different body parts back in time, recognizing when each one first appeared, often in a quite different form from what we have in our human bodies now, and they can follow how each body part has evolved.  Paleontologist Neil Shubin has explored this approach in a recent book.19

     Focusing on the human body has the dramatic effect of making the geological time periods come alive.  Take the Ordovician, for example.  As noted above, there are Ordovician glacial deposits in the middle of the Sahara.  For most people, other than geologists, that may be mildly interesting, but it is pretty remote from more pressing, daily considerations.  But what if we tie the Ordovician to our own bodies? 

     You can do this by putting your hands up to your face and feeling your jaw.  You can feel the mandible that moves up and down.  You can feel the muscles, just below the ear, that make it move.  And just in front of the ear, you may be able to find the joint where the jawbone articulates with your skull.

     The jaw is immensely important to us humans.  It allows us to chew and eat and drink, to talk and sing and recite poetry.  So, how far can we trace it back?  The jaw first appeared in our ancestors in the Ordovician—while those south-pole glaciers were covering the frozen Sahara.  The jaw first appeared in a branch of the tree of life—a "clade"—called the Gnathostomata—meaning "jaw-mouth"—and we humans are members of that clade.20  So we each carry a souvenir of the Ordovician with us every day of our lives, and we use that Ordovician heritage every time we move our jaw, open our mouth, and eat or talk or sing.

     So our bodies help us to understand the history of evolution and vice versa, and to tie all that to the geologic history of our planet.21  For example, the opposable thumb that allows us humans to make the delicate manipulations so important in tool use and music making is a recent development within our primate ancestors.  Hair and sweat glands go back further, to the origin of mammals.  Arms and legs are older than that, tracing back to some lobe-finned fish, before the first animals learned to live on land.  Jaws came before that, in the Ordovician.  The bilateral symmetry of our body, left and right, and the origin of the body itself, of multicellularity, both go back to around 600 million years ago;  the earliest known bodies are recorded as impressions in sedimentary rocks of that age.

*          *          *

     Back beyond the history of Humanity, Earth, and Life, lies the history of the Cosmos, leading us further into the disturbing realm of deep time.22  Immediately after the creation of the Universe in the Big Bang, fourteen billion years ago, no stars had yet formed and there were no sources of light in the Universe.  This is a time that cosmologists call the Dark Age, and it reminds us of the human dark ages after the destruction of the Bronze Age civilization and Rome, and the paleontological dark ages after the six great extinctions of life.

     Shortly after the Big Bang, the only atoms in the universe were hydrogen and helium, which can make only gases, not liquids or solids, so no Earth-like planets could form early on.  All the other elements needed to make Earth and to make life—silicon, carbon, oxygen, iron and so on—were cooked up inside stars by the nuclear fusion that makes them shine, and were dispersed into space by the gigantic star explosions called supernovas. 

     Those elements came together to form our Earth 4567 million years ago.23  Now there is an easily remembered date!   To put things in context, the Ordovician is about one tenth that age—around 456 million years ago.  And the preceding historical cycle of supernovas is where all of our bodies, and all of our Earth came from, except for the hydrogen.  As Carl Sagan once wrote, we are "… starstuff, pondering the stars."24

     When we ponder Cosmic history, and all those stars, we receive another assault on our egos, compounding the assault of deep time, for deep space is so vast that we simply cannot comprehend it.  There are about a hundred billion stars in our galaxy, and about a hundred billion galaxies in the cosmos.  Astronomer Brent Tully at the University of Hawaii has made available a wonderful computer simulation of flying through our own galaxy at hypervelocity, with stars rushing by like blown snowflakes in the headlights.  And then the simulation leaves our galaxy and finally flies through uncountable other galaxies, in their turn like blown snowflakes in the headlights.25

*          *          *

     And so, our too-quick tour of Big History leaves us fascinated by the exotic events we have witnessed, but sobered and perhaps depressed by the realization that we are an infinitesimal, un-noticeable speck, lost in the overwhelming vastness of deep time and deep space.  If we are manifestly not the center of everything, if we are a tiny speck lost in time and space, how can we make sense of our human existence?  How can we have any meaning at all?

*          *          *

     One intriguing possibility may come from the observation that in all four regimes we can identify continuities (where knowing the situation last year lets you predict more or less what will happen next year), and contingencies (where historical patterns change suddenly and unpredictably).26  Both continuities and contingencies are everywhere, in all kinds of history, and the contingencies are so utterly unpredictable that, for me, they make the idea of predestination ridiculous.  Military battles are notoriously contingent.27  The classic example goes:  "For want of a nail the shoe was lost, for want of a shoe the horse was lost, for want of a horse" … and so on until the battle, and even the kingdom are lost—because of a missing horseshoe nail. 

     Each of us came to be born only because of the most insanely improbable set of historical contingencies, and it is astronomically more likely that someone else would have been born, and we contemporaries alive today would never have existed.  Just think for a moment about your family tree—if you could write out every one of your ancestors on a gigantic sheet of paper.  You have two parents, four grandparents, eight great-grand parents, and so on—another power of two with each generation—back to the earliest multicellular organism and beyond that to single-celled creatures.  How many boxes are there in your family tree that far back?  If we assume one year per generation, on average, then back at the beginning of sexual reproduction there are two-to-the-one-billion-power boxes in your family tree.  (Obviously you did not have that many actual ancestors, because not that many individuals were then alive, so you are descended from the same ancestors by many different routes.)

     Now think about this:  The sex of an individual is established, more or less randomly, at conception, and if even one of your hundreds of billions of ancestors had turned out to be the opposite sex, they could not occupy that place in your family tree, and you would not exist.  Someone else would, but not you—not the exact you, with your particular genetic makeup and your particular life experiences.  Each one of us is breathtakingly improbable. 

     In our voyage through Big History, we have met deep time and deep space, and now we are meeting what I have started to call "deep improbability."  To illustrate how deeply improbable we each are, let me tell you a story of contingency and improbability in my family's trajectory, to show how unlikely my own existence is.  The point of the story is to suggest that you think about how unlikely you are as well. 

     My great great grandfather, Eugenio Fernández Martínez, was a farmer from northern Spain in the early nineteenth century.  Somehow he had obtained a position as palace manager for the Prince Francisco de Paula in Madrid, and had arranged for his sons to attend the palace school with the son of the prince.  But before that could happen, while accompanying the prince to Bilbao, great great grandfather was killed in a fall from a balcony.  As a result, school in the palace was out of the question, and his youngest son, Luis Fernández Álvarez, now seven and an orphan, had no possibilities in Spain and had to emigrate to Cuba with his older brother.  Subsequently he came to the United States, became a medical doctor, and founded our California family.

     Every time I think of my great great grandfather's early death I feel sad, but I also realize that without that highly unlikely contingency, his son would probably never have left Spain, and all of his California descendents, including me, would never have existed.  When I tell this story to my students or to anyone else, I invariably hear lots of other interesting stories of unlikely meetings and marriages in their families.  Deep improbability is everywhere in our family trees, and each of is unlikely to a degree we can barely comprehend.

     To be more quantitative, if we ask how many individual people will be born into the next global generation, the answer is something like a billion, about 109.  To give you a graphic idea of this number, a billion grains of fine sand is a double handful.  If we calculate how many different individuals might possibly be born in the next global generation, considering the number of women's eggs available, and the number of sperm that might fertilize them, the answer is around 1024, and that number of grains of sand would fill the Grand Canyon!

     We contemporaries, alive today, are the extraordinarily improbable individuals who did get conceived and born (the handful of sand), out of all the others (the Grand Canyon full of sand) who might have been, but never got to be.  I sometimes picture an endless cloud of souls out there—the ones who never got to live.  And when you think that these extraordinary odds are multiplied with every generation back to the beginning of sexual reproduction, you see that each of us is unlikely to a degree that utterly defies imagination.  The odds against each of us being here dwarfs the number of stars in our galaxy, it dwarfs the number of stars in all the galaxies, and it dwarfs the number of atoms in all the stars in all the galaxies in the entire universe.  Deep improbability is far more astonishing than deep time or deep space.

*          *          *

     What should we make of all this?  I guess my reaction is to say, "Congratulations!  We all made it!  We each have won, in the most formidable game of chance ever conceived."

     What does deep improbability mean for us?  One friend of mine, when I told him this story, said, "So why are we always hating and killing each other?  Every day should be a celebration, relishing the fact that we are all on this Earth together." 

     Not everyone will have that reaction, of course.  Another time I told this story, a crusty old Berkeley mathematician said, "Well, I can think of a few people I wish had not made it."

     But even so, thinking about deep improbability has changed the way I view the world.  It has made me think of each person I meet as a demonstrated winner, as a precious soul who has survived the most ruthless culling process ever devised.  As a potential friend and companion.  Maybe you will find yourself thinking this way as well.

     Here is the power of Big History—to make us see our world in a different way, in a way that just might help us in the face of the awful problems we confront. 

*          *          *

     After a semester in which my wonderful Berkeley students saw how all of history fits together, a semester in which they really did develop historical mindedness as an intellectual tool and a habit, and in which they struggled with the implications of deep time and deep space, we came to the last class, and we talked about how deeply improbable each of us really is, and about what this might mean for the way they choose to live their lives.  More than a few of my students had tears in their eyes as we came to the end of the hour. 

     Their reaction hints at the importance of fully understanding the entire past—the Big History—that has led to us human beings and the world we live in.

Walter Alvarez is a professor in the Earth and Planetary Science department at the University of California, Berkeley. He is perhaps best known for the theory that dinosaurs were killed by an asteroid impact, developed in collaboration with his father, Nobel Prize winning physicist Luis Alvarez (see W. Alvarez, T-Rex and the Crater of Doom, Princeton University Press, 1997).  As well as an interest in big history, Professor Alvarez has contributed to our understanding of Mediterranean tectonics, Roman geology and archaeology, and the establishment of magnetostratigraphic correlations.  Professor Alvarez has won numerous awards and honors, including the prestigious 2006 Nevada Medal, the Vetlesen Prize, and the Penrose Medal, the Geological Society of America's highest award. He can be contacted at


1 Christian, D., 2004, Maps of time.  An introduction to Big History: Berkeley, University of California Press, 642

2 Spier, F., 1996, The Structure of Big History: Amsterdam, Amsterdam University Press, 113

3 Alvarez, W., 2009, The Mountains of Saint Francis: New York, W. W. Norton, 304

4 Barry Rodrigue, at the University of Southern Maine, has compiled a list of the known Big History courses at the college level.

5 Menocal, M.R., 2002, Ornament of the world: How Muslims, Jews, and Christians created a culture of tolerance in  Medieval Spain: New York, Little, Brown and Co., 315; Lowney, C., 2005, A vanished world: Muslims, Christians, and Jews in Medieval Spain: Oxford, Oxford University Press, 320

6 Nur, A., 2008, Apocalypse: Earthquakes, archaeology, and the wrath of God: Princeton, Princeton University Press, 309;  Drews, R., 1993, The end of the Bronze Age: Changes in warfare and the Catastrophe ca. 1200 B.C.: Princeton, Princeton University Press, 252

7 Renfrew, C., 2007, Prehistory:  The making of the human mind: New York, The Modern Library, 219;  Goudsblom, J., 1992, Fire and civilization: London, Penguin, 247

8 Finlayson, C. and 25 co-authors, 2006, Late survival of Neanderthals at the southernmost extreme of Europe: Nature, v. 443, 850-853.

9 Johanson, D., and Wong, K., 2009, Lucy's legacy: the quest for human origins: New York, Random House, 320

10 Hsü, K.J., 1983, The Mediterranean was a desert: Princeton, N. J., Princeton University Press, 197; Ryan, W.B.F., 2009, Decoding the Mediterranean salinity crisis (p 95-136): Sedimentology, v. 56, 95-136.

11 Loget, N., and Van Den Driessche, J., 2006, On the origin of the Strait of Gibraltar: Sedimentary Geology, v. 188-189, 341–356.

12 Alvarez, W., Claeys, P., and Montanari, A., 2009, Time-scale construction and periodizing in Big History: from the Eocene-Oligocene boundary to all of the past: Geological Society of America Special Paper, v. 452, 1-15.

13 Alvarez, W., 1997, T. rex and the Crater of Doom: Princeton, NJ, Princeton University Press, 185

14 Alvarez, W., 2003, Comparing the evidence relevant to impact and flood basalt at times of major mass extinctions: Astrobiology, v. 3, 153-161.

15 Excellent maps of former continental positions are available on the website of Gérard Stampfli at the University of Lausanne (

16 Li, Z.X., and 15 co-authors, 2008, Assembly, configuration, and breakup history of Rodinia; a synthesis: Precambrian Research, v. 160, 179-210.

17 Caputo, M.V., and Crowell, J.C., 1985, Migration of glacial centers across Gondwana during Paleozoic Era: Geological Society of America Bulletin, v. 96, 1020-1036.

18 Cracraft, J., and Donoghue, M.J., ed., 2004, Assembling the tree of life: Oxford, Oxford University Press, 576

19 Shubin, N., 2008, Your inner fish: a journey into the 3.5-billion-year history of the human body: New York, Random House, 240

20 Rowe, T., 2004, Chordate phylogeny and development, in Cracraft, J., and Donoghue, M.J., eds., Assembling the tree of life: Oxford, Oxford University Press, 384-409.

21 Knoll, A.H., 2004, Life on a young planet: the first three billion years of evolution on Earth: Princeton, N.J., Princeton University Press, 277

22 Smoot, G., and Davidson, K., 1993, Wrinkles in time: New York, Morrow, 331; Dauber, P.M., and Muller, R.A., 1996, The three Big Bangs: Reading, MA, Addison-Wesley, 207;  Chaisson, E., 2006, Epic of evolution: seven ages of the cosmos: New York, Columbia University Press, 478

23 For an explanation of how the age of the Earth is determined, see Dalrymple, G.B., 1991, The age of the Earth: Stanford, Calif., Stanford University Press, 474

24 Sagan, C., 1980, Cosmos: New York, Random House, 345


26 Gaddis, J.L., 2002, The landscape of history: Oxford, Oxford University Press, 30

27 Cowley, R., ed., 1999, What if?: The world's foremost military historians imagine what might have been: New York, Berkley Books, 395



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