Suppose, just suppose, you were somewhere out in space, beyond the confines of the solar system, and that you were in radio contact with an alien, a friendly alien, from another part of the galaxy. And suppose, just suppose, that in chatting about things in general, you wanted to describe your home, the place where you live or had grown up. Not that small town in New Hampshire, or that particular suburb of Los Angeles or Cape Town or London, but the planet, Earth—the home planet. How would you identify it? How would you give some sense of where...

Though we know our neighborhood like the back of our hand, the Earth itself, the larger place that includes all our neighborhoods, is a strange place. This homestead, at once so stable, is spinning, we’re told, and spinning fast at about 1,000 miles per hour. This secure dwelling, this sturdy foundation, is also hurtling around the Sun at 66,600 miles per hour; that’s 18.5 miles per second.

It’s unsettling, contradictory, bewildering, even intimidating. So let’s step back and get a sense of our position. Just where are we? How can we get a useful sense of the place we call...

We travel together on this remarkable planet Earth, plunging through the darkness of space at nearly 67,000 miles per hour, as well as moving around our star, the Sun, at 66,000 miles per hour, at just the right distance to allow us to live. It is this distance that makes Earth neither too hot, thus allowing liquid water to remain here, nor too cold, which would freeze it all, with an atmosphere dense enough to allow animals to breathe and plants to respire but not so dense as to filter out sunlight. And our planet’s molten nickel-iron core produces an...

Almost all homes have numbers. A few have names. I’ve lived in twenty houses over my lifetime, but only two had names. The first was called “Pilgrim Cottage.” It was in Wales, close by the sea. We rented it while our own home was being built nearby. We liked the name, it was modest: “cottage” not “hall” or even “house.” Still less, “grange” or “manor.” And it had a nice ring to it. After all, like it or not, we are all tenants, temporary residents, and therefore pilgrims. Our landlords did not like the name so they changed it, and...

Seen from space, Earth is a marvelous azure-blue sphere, illuminated with jewel-like clarity by the light of the sun. But it is a sphere that is always partly veiled, with changing, diaphanous filaments of cloud, some small, and some so vast that they seem to encircle the planet. These clouds are the visible part of the atmosphere. Mars has an atmosphere so thin that the red planet is never cloud-covered, Venus an atmosphere so chokingly dense that its rocky surface is never visible. But Earth’s remarkable envelope of air makes life possible by enfolding the planet in a protective embrace...

Life is a hazardous business, but our species has elevated survival to a high art by making individual health care and public health national priorities. We live sensibly, we eat prudently, we exercise doggedly—at least some of us do. We legislate elaborate safety standards and costly safeguards, and we devote sustained attention both to protecting and prolonging life. We make a huge investment—more than 10 percent of the gross national budget—in health care. And so we should. Our views of human worth and individual dignity demand it.

And the results are impressive; the benefits real. Human longevity...

Perhaps our forebears always had an intuitive sense that they inhabited a place of great antiquity. All civilizations seem to have had an interest in the beginnings of things, and each had its own account of origins. The ancient Brahmans believed the Earth to be eternal. So, it seems, did Aristotle, who thought it inappropriate to consider Earth to be just as much an aging creature as humans are. Others proposed a definite age, and as early as 450 BC Herodotus had suggested that the slow rate at which the waters of the Nile deposited the sediment that formed its...

We are a young species, a recent arrival among the creatures with whom we share the planet we call home. But our lineage is venerable: we are youthful members of an old and successful family, long established on an ancient homestead. Like most youngsters, we still owe much to our parents; we are reliant to some degree on the creativity and industry of our forebears, and wholly dependent on the rich variety of products and bountiful fruits of the expansive estate and fertile homestead we have inherited from them.

For all our casual sophistication, declared independence, and supposed self-sufficiency, we...

We dwell on a changing planet whose surface is in constant flux: atmosphere and oceans, land and sea, air and water, rain and soil, all interact in ceaseless cycles, some very long and some very short. Cliffs crumble, coastlines erode, new volcanic islands appear, ancient cities are buried under blowing sand, estuaries and harbors become silted up. But these surface exchanges, and others like them, though locally conspicuous, are scarcely significant on a global scale, or even in a human time frame. Certainly, over geologic time, over millions of years, mountains come and go, and vast landscapes are submerged by...

Within the vastness of our solar system, Earth is, as we have seen, a singular planet: singular in its temperature, singular in its atmosphere, singular in its oceans, singular in its composition, singular in its crust and its core and their distinctive interaction, singular in the activity we call life. For all we know, it may well be singular in its degree of singularity. Though we know of other planets beyond our solar system, we know almost nothing, as yet, about their characteristics.

But what we do know about Earth is that its singularity owes everything to its location: third...

The universe, as we have seen, is some 13.7 billion years old; the solar system is much younger, having been formed, together with the Earth and other planets, about 4.6 billion years ago. This date is based on the oldest ages of meteorites, which are thought to represent the oldest solid material in the solar system. The oldest known Earth rocks, however, were formed “only” some 3.7–3.8 billion years ago. The time interval between these two ages—3.7–4.6 billion years ago—is known as the Hadean Era, from the Greek word Hades. This era is well named, for...

“In the beginning …” For all its haunting familiarity, it’s a phrase that touches life’s most obscure mystery and raises its most profound questions: “Where did we come from?” “How did we come to be?” “How did life come into existence?” “Are we alone in this vast, cold universe?”

We know nothing, as yet, of life elsewhere in the universe. Does life—whatever its form, whatever its precise definition—exist elsewhere in the far reaches of the cosmos? Has it ever existed on one of our neighboring planets? May it be, perhaps, a frequent feature of planets like ours? Or...

“Stop climate change,” exhorts the bumper sticker. It’s a laudable ambition but an impossible task. Climate change has been an ongoing process for as long as the Earth has existed. That’s 4.6 billion years. Earnest as these pleas and warnings about global warming undoubtedly are, they can be addressed only if we understand their context. Earth’s temperature has always varied. The only times Earth has not been warming are when it has been cooling. It is never constant over any significant time span. Nor can it be. The dynamic system that climate reflects is the same system that sustains us....

On June 22, 1969, the residents of Cleveland, Ohio, were startled to find the Cuyahoga River on fire—again! The river, which passes through the city on its winding one-hundred-mile way to Lake Erie, had long been heavily polluted from the cumulative effects of waste dumping, sewage disposal, industrial contamination, agricultural runoff, growing urban development, and dam construction. But pollution was one thing; a blazing river was quite another. It was, wrote one reporter, “the river that oozes rather than flows.”

That fire, and the press attention it created, not only generated a torrent of legislation—local, state, and national...

We share our benevolent planet with some 7.0 billion other members of the human race. By 2050 that global population is projected to increase to some 9.6 billion, before declining and leveling off at about 8.5 billion. If these projections prove to be correct, that will mean feeding about 50 percent more people than we now have.

Does that imply looming catastrophe, as some argue? Or is it, rather, a manageable challenge and a solvable problem?

Some conclude that this is a manageable task while others believe we already face a serious crisis. Thus, David Pimentel et al. argue that...

For the last 3.5 billion years the Earth and its systems have shaped the lives and influenced the behavior of all its inhabitants. And the inhabitants, in turn, have had a significant impact on the surface of the planet that gave them birth. Think, for example, of the huge influence of early bacteria in providing the initial oxygen of the atmosphere. Or consider the continuing role of plants in the carbon cycle.

But for most animals, this interchange has been more one-sided. Earlier generations of humans were, like most of their fellow creatures, far more dependent on Earth’s bounty and...

To Thales of Miletus (ca. 625–546 BC), the first of the Greek philosophers, water was Earth’s most basic substance, its most elemental component. It was, he believed, the vast reservoir in which the disklike Earth floated, surrounded by the great hemisphere of heaven. Water, he argued, was the basic stuff of the universe. That’s not surprising, perhaps. Humanity, after all, exists within an envelope of water.

The oceans and seas surrounding the continents were once seen as boundless. The surface of the land was itself interlaced with streams, rivers, lakes, springs, and swamps, carrying water in an endless cycle...

If Earth is our dwelling place, air is our enfolding mantle. We spend our lives bathed in air, enveloped in its encompassing embrace. It provides our every breath, it supports our every activity. Every morsel of food we consume is a gift of air, a product of the ancient alchemy of photosynthesis, by which plants withdraw one component of the air (carbon dioxide) and so create another (free oxygen). Air encloses the water of the planet, evaporating here, precipitating there, responding in its movements to the radiant energy of the Sun as it drives the water cycle and powers the...

Time and time again in human history, from ancient Mesopotamia to modern Madagascar, poor animal husbandry and irresponsible farming have led to soil erosion that destroyed the productivity of the once-bountiful land. We are in danger of allowing a similar destruction, not in a single region or on a large island, but over a vast area of continental proportions and global extent.

Soil is Earth’s detritus: the weathered, eroded skin of its crumbling surface, mixed with the decaying remains of the vegetation it supports. In some places—mountaintops, high plateaus, the polar regions—soil scarcely exists, for there is little...

In 1944, twenty-nine reindeer were released on St. Matthew Island, Alaska, a thirty-two-mile-long by four-mile-wide island in the Bering Sea. The purpose was to provide an emergency food source for the members of U.S. Coast Guard who were temporarily stationed there. With the end of World War II the island had returned to its earlier uninhabited state: a “reindeer paradise” of thick lichen mats and no predators. By 1957 the reindeer population had reached 1,350, most of them fat and in excellent shape.

By 1963 the reindeer population had swelled to six thousand, though they looked less healthy and the...

It is always tempting to identify one particular issue as the most significant issue of our time. “What,” we might ask, for example, “is the most critical need for a sustainable planet?” Well, clean water, adequate food, unpolluted air, fertile soils, healthy ecosystems; the list might start with those, and certainly each of them is of vital importance. But if the planet is to have a human population of anything like its present size—let alone a population of half as many again, all demanding mobility and rising standards of living—we’d also have to place energy high on our...

Human history, as we have seen, is often divided on the basis of the materials that have characterized successive cultures: the Stone Age, Copper Age, Bronze Age, Iron Age, and so on. These substances and others have not only provided the material basis for civilization but have been so valuable that empires have been established, wars have been fought, and nations have been both created and destroyed in competition for their supply. The age of petroleum, in which we still live, provides striking examples.

We’ve already discussed some of the materials on which we are most dependent: petroleum, coal, air,...

Any discussion of the prospects for our long-term tenancy requires a survey of the general state of the property and an understanding of the impact of our occupancy. Earth is an ancient and resilient planet, constantly undergoing change in both its inhabitants and its surface geography. And though it derives most of its energy from its parent star within the solar system, it is otherwise, in broad terms, self-contained and self-renewing, at least over long cycles of time. Perhaps 98 or 99 percent of all Earth’s species that have ever lived are now extinct. It is as idle to pretend...

There is, in the pursuit of sustainable development, the need for some modesty. Earth’s ecosystems have undergone great change in the past, and they will continue to undergo change—most gradual, but some rapid—with or without any human interaction. But on that pattern of natural change we have imposed our own human influence. Much of our economic and social progress over the last two centuries has been made at the expense of these natural ecosystems. We need to recognize how critical a role these systems play in maintaining and stabilizing the resources and environment on which our continuing well-being...

Four and a half billion years ago Earth came into being, as a spinning, swirling cloud of hydrogen, helium, and dust slowly condensed to give birth to the Sun and its family of protoplanets. For aeons, the newborn planet was “without form and void,” desolate, devoid of life, convulsed as impact followed impact and collision imploded on collision. Bombarded from without by the continuing rain of cosmic debris, Earth was also heated from within by its own growing radioactivity, so that gradually its temperature rose. Later, its slowly hardening surface crust was repeatedly ruptured by violent volcanic outbursts and explosive...