Our Imperiled World

It took billions of years to make the earth habitable for humans. A distinguished astronomer warns the United Nations how quickly that can be reversed.



This essay is adapted from reflections presented to the United Nations General Assembly on April 18, 2012.


I’m holding in my hands two ball bearings, each about two centimeters in diameter. I propose to build a model of our cosmic environment here at the United Nations Headquarters in New York. The first sphere represents the sun. On this scale Earth will be two meters away, and much too small for you to see it. Mars, even smaller, will be another meter farther from the sun. On this scale, where should we place the second sphere, representing the closest star to our own solar system? On top of the Empire State Building? At JFK? Much too close! It should be placed some distance beyond Toronto.

These stars are but two among the 200 billion in our Milky Way Galaxy. That’s some 30 stars apiece for every man, woman, and child on Earth. On the scale of our ball-bearing model, the Milky Way would go far beyond the moon! So now let’s collapse our model by 10 billion times, such that our disk-shaped, pinwheel galaxy would be the size of a two-euro coin. Now where should I place a second two-euro coin to represent the next closest major spiral galaxy? In London? Be surprised! The coins should be only about 60 centimeters apart. Collisions between stars are fantastically rare because stars are so far apart, whereas collisions between galaxies are common because the galaxies are relatively close together, though the collisions take ages to happen.

A most curious and interesting fact about the distant galaxies is that they are rushing away from each other, and the farther they are from us, the faster they are going. It’s as if an immense explosion took place, as indeed it did, and the faster fragments are the farthest away. We can calculate from the speeds and distance when that explosion happened, 13.7 billion years ago, the creation of the universe, and the creation of time itself. This means we live in a universe with a history, a universe that has been changing throughout time. It is the history of the universe, and our place within it, that I want to sketch briefly.

In the first three minutes of that fiery Big Bang, the two lightest elements were created, hydrogen and helium. Fire of sorts existed, yes, but no earth or air, and no water because there was no oxygen for H2O. The Big Bang was over before the heavier elements had a chance to form.

The oxygen for our air and water and the carbon for our bodies were made very slowly over the next billions of years in the hellish cauldrons in cores of evolving giant stars. Occasionally they would explode as supernovas, throwing into interstellar space the heavier elements, including carbon and oxygen for our proteins, phosphorus for our DNA, and iron for our blood (plus gold to plate our satellites and uranium for our reactors). We are all born of the stars, our bodies recycled star stuff. In time there were enough heavy elements for our sun and planetary system to form. That was just short of five billion years ago. At first Earth was a barren, volcanic place, battered by impacts of assorted asteroids, without permanent oceans or atmosphere. As the environment settled down, water vapor spewed forth from the volcanoes and condensed to form oceans. An atmosphere laced with carbon dioxide began to form. In those early days in the history of our solar system, the sun was not so bright as it is now, and it took as much greenhouse effect as the carbon dioxide could provide to keep the oceans from freezing solid.

Happily, the early atmosphere did not have too much oxygen—oxygen is a very active element, rusting any unprotected iron, and quite poisonous to the original living material. Early single-celled organisms slowly converted carbon dioxide into free oxygen, and the oxygen content of the atmosphere rose to around 20 percent in time to provide more efficient fuel for the more complex life forming on Earth in the Cambrian period, about 500 million years ago. So then our planet had water and air, and gradually it began to form the agricultural element earth—that is, soil—so the greening of the continents could take place. As I indicated, our planet Earth has a history, and a complex one that took hundreds of millions of years to form the habitable surroundings we have today.

In the past 500 years, ever since Copernicus invented the idea of a solar system in which Earth was just one of a family of planets cycling around the sun, human beings have wondered whether there are other habitable planets cycling around other stars, and whether habitable planets might indeed be inhabited by other sentient beings. In the past two decades astronomers have started finding other planetary systems. Currently the Kepler mission, a space-borne observatory, monitors the magnitudes of 150,000 stars to find the small dimming caused when a planet passes in front of a star. The project now has about 3,000 candidate stars, where a temporary change in brightness indicates a planet might be present. The goal of the project is to find Earth-sized planets cool enough to provide a habitable environment in which life may have arisen.

But is a habitable environment enough to guarantee that life will form there? That is a giant question that scientists would like to answer, but first they would simply love to know whether life has formed in at least one other place in our galaxy. Or are we alone? For about two billion years, the life on our planet was so primitive that it could scarcely have been detected from afar. Not until our atmosphere had gained enough oxygen would there have been a potential signal that something special was happening here. As I have mentioned, oxygen is a very active element, and unless it is continuously replenished, it will rust away, so astronomers hope eventually to find a planet where an oxygen atmosphere can be detected spectrographically. The discovery of such a signal will be a truly exciting event, because the presence of oxygen would suggest that there was some chemical activity, most probably some sort of life, to continuously replenish it. But such a discovery would leave more questions unanswered than answered, because that signal would not reveal what kind of life was out there.


Many years ago I heard a fascinating lecture by the late Philip Morrison, an institute professor at MIT. It was entitled “Termites and Telescopes.” He began by stating that human beings were supposedly the only creatures technologically advanced enough to construct arches, something the Romans first used for building bridges. But, he pointed out, termites had learned to build arches long ago, using them in constructing their impressive nest structures. Morrison then asked a provocative question: Could termites ever discover how to build telescopes? Building nests is a quintessential example of instinct, some inheritable chemistry in the termites, poorly understood, but something that took eons to become embedded in their genetic structures. Presumably, if the termites were ever to build telescopes, it would take millions of years to code the instructions into their genetic chemistry.

Early in the 19th century, the French botanist Jean-Baptiste Lamarck proposed an evolutionary system whereby acquired knowledge could be inherited, in contrast to Darwin’s later theory that variations are chosen by natural selection, a very slow process indeed. Morrison chose his apparently ridiculous example of termites and telescopes to paint the contrast between the slow, trial-and-error learning process of biological evolution and the rapid cultural evolution where newly acquired knowledge can be passed on from one generation to another in other ways than genetic coding—books, for example. Biological evolution has brought Homo sapiens to the Lamarckian divide, to the stage of cultural evolution where more information can be carried in our brains than in our DNA. Termites are still unimaginably far from building telescopes, whereas for us telescopes were invented a mere 400 years ago, but are now universal.

The almost incredible speed of scientific discovery and technological development is transforming the world at a dizzying rate. Our great-great-grandparents would be far more at home in the world of Christopher Columbus and Nicolaus Copernicus than our world of today. One hundred and twenty-five years ago, no one knew about X-rays or radioactivity or the inner structure of atoms. Automobiles, communication by radio, and airplanes still lay in the future. Sixty years ago, when I was a graduate student, biochemists and anatomists did not yet know precisely how many chromosomes were found in human cells. Mobile phones were something for comic strips and science fiction. Lasers were unknown. Today I have a dozen in my house.

In 1955 I had a wonderful opportunity to participate in an expedition to observe a total solar eclipse in Ceylon. Thirty-two years later, in 1987, I was able to return to the eclipse site, and I was asked what did I notice that was different. I mused that Sri Lanka seemed much more crowded than Ceylon had been. That’s right, our tour guide responded. The population had doubled in those three decades. Since 1900 the entire world population has quadrupled. The physical mass of human beings and domesticated animals now makes up 90 percent of the vertebrate mass, up from 0.1 percent 10,000 years ago.

The accelerating expansion of technological power, combined with the explosive growth of the world population and unsustainable consumption and production patterns, brings unparalleled challenges for the unity of nations. Already some centuries ago the expanding human population began to change the environment. Today, humans have modified more than 80 percent of Earth’s land surface.

The passenger pigeon, a bird whose giant flocks once darkened the skies of the American Midwest, is no longer alive. Neither is the giant moa or the Irish elk. Several months ago I met a paleontologist who works on recent vertebrate fossils. She informed me that 60 vertebrate species just in Hawaii have gone extinct since the human population (with their associated rats) arrived in the islands.


Around the world, numerous species, including some we don’t yet know about, are being threatened by deforestation and other major environmental changes. This is the competition between human population growth and older environments. Recently I visited the Lemur Conservation Foundation Reserve in Florida. These endangered primates from Madagascar are our distant cousins. Madagascar is a particularly fruitful place for studying the antecedents of Homo sapiens because it was isolated from Africa and uniquely preserves early species from the primate family. Today space pressures from the human population in their native land may well doom the future of many lemur species, though the Florida reserve may slow this catastrophe.

I have in my hand a shell of the Manus Island green tree snail. These attractive shells cannot be sold in the United States because the snails are listed as an endangered species. Although abundant in New Guinea, this species is threatened by loss of environment. Since the shell cannot be sold, there is no profit in letting the snail survive. I mention this in passing as a miniature case to show how ambiguous are many of the situations facing all of us attending this session of the UN General Assembly.

Our planet works as a biophysical system that creates soil and its fertility. As the conservation biologist Thomas Lovejoy has pointed out, ecosystems provide a variety of services, not least of which is clean and reliable water. Biological diversity is the essential living library for sustainability. If we ourselves survive, in the distant future our age may well be known for the greatest loss of biological species since the extinction of the dinosaurs.

The expanding human population has the power to alter the environment not only on land but also in the sea, through the runoff of pollutants such as nitrogen fertilizers. And we have also begun to modify and poison our atmosphere. A case in point, though now a rare success story, was the discovery in the 1970s and early ’80s that the ozone layer in the stratosphere was being depleted in large part because of the release of chlorofluorocarbons used in refrigerants and aerosols. It is the ozone layer that filters out ultraviolet radiation, which can cause skin cancer and cataracts. Despite one leading industry spokesman who maintained that all this was “a science fiction tale, a load of rubbish, and utter nonsense,” the scientific evidence soon established ozone depletion as a genuine manmade threat, which led to the 1987 Montreal Protocol to phase out the manufacture of these chemicals. Eventually UN Secretary General Kofi Annan stated that this UN-backed treaty was “perhaps the single most successful international agreement to date.”

Having crossed the Lamarckian divide, Homo sapiens has now brought with astonishing speed many scientific and technological advances, including color television, the polio vaccine, and the Internet. But for the first time in history, humankind has now also stolen the secrets of the stars, bringing to Earth the power to wipe out all the higher forms of life. A nuclear disaster is not just science fantasy. The Chernobyl and Fukushima accidents give hints of the unintended devastation that can occur. Consider the destruction that could be wrought by a delusional madman or a deliberate anarchist. A hair-trigger response by a paranoiac society could bring an unplanned Armageddon to all the cultures of this world.

We do not know whether there are other cultures and civilizations out there among the 200 billion stars in our galaxy. But if there have been and if they managed to blow themselves to bits within a century or two after getting the technology to communicate across space, it would be featherbrained to think of finding an active alien outpost, because such limited communicable lifetimes are mere specks in the billions of years it takes to evolve a civilization.

We recently saw the 100th anniversary of one of history’s greatest maritime tragedies, the sinking of the Titanic. Just a few weeks before the anniversary, a menu for the last first-class luncheon aboard that ill-fated ship was auctioned for $122,000. Imagine the hundreds of guests sitting in that luxurious dining room, with a wide choice of courses, never dreaming that in a few hours many of them would be drowning in the icy waters of the North Atlantic as that great ship went to the bottom of the sea.

Today we are on a great ship, planet Earth, cruising through mostly empty space, little dreaming that humankind now has the means, in a split second, to destroy this entire city, to render this entire region radioactively uninhabitable for generations to come, and to destroy civilization as we know it. It may not happen here. Perhaps it will happen to Jerusalem and the much-contested Holy Land, which would then be radioactively quarantined for every faith.

Or it may be something subtler. Atmospheric carbon dioxide levels are now higher than at any time in the past several million years, perhaps even back to the warm period following the dinosaur extinction 64 million years ago. For the first time in thousands of years, a large part of the Arctic Ocean is no longer capped by sea ice through the entire year. On every continent the timing of flowering plants and the migrations of birds are changing in response to warming conditions. Butterflies formerly known only in the southern United States have now turned up in substantial numbers in New England. Within just a decade our climate could reach a tipping point, at which irreversible changes will heat our fields and forests beyond recognition.

We are at a perilous point, where our knowledge, our power, and our population give us the capability to irredeemably wreck our environment. Never has more been asked of diplomacy, and never has so much hard and dedicated work been required from men and women like you. Our world hangs in the balance. Don’t let this unique cosmic ship sink to the bottom of the sea.

Permission required for reprinting, reproducing, or other uses.

Owen Gingerich is professor emeritus of astronomy and of the history of science at the Harvard-Smithsonian Center for Astrophysics.


Please enter a valid email address
That address is already in use
The security code entered was incorrect
Thanks for signing up