Not-So-Lonely Planet
By OLIVER MORTON
San Francisco

NY TIMES OP-ED Published: December 24, 2008

They came for the Moon, and for the first three orbits it was to the Moon that the astronauts of Apollo 8 devoted their attention. Only on their fourth time round did they lift their eyes to see their home world, rising silently above the Moon’s desert plains, blue and white and beautiful. When, later on that Christmas Eve in 1968, they read the opening lines of Genesis on live television, they did it with a sense of the heavens and the Earth, of the form and the void, enriched by the wonder they had seen rising into the Moon’s black sky.

The photograph of that earthrise by the astronaut Bill Anders forms part of the Apollo program’s enduring legacy — eclipsing, in many memories, any discoveries about the Moon or renewed sense of national pride. It and other pictures looking back at the Earth provided a new perspective on the thing that all humanity shares. As Robert Poole documents in his history, “Earthrise: How Man First Saw the Earth,” that perspective had deep cultural effects, notably in the emotional resonance it offered the growing environmental movement. Seen from the Moon, the Earth seemed so small, so isolated, so terribly fragile.

It takes nothing from the beauty and power of the image, though, to point out that it was the photographer, far more than its subject, who was isolated, and that the fragility is an illusion. The planet Earth is a remarkably robust thing, and this strength flows from its ancient and intimate connection to the cosmos beyond. To see the photo this way does not undermine its environmental relevance — but it does recast it.

That the Earth is small is undeniable. If the inner solar system were the size of the United States, the Earth would be the size of a football field; if the distance to the center of the galaxy were a mile, the Earth would be less than an atom. But if the “Earthrise” photo could have captured our planet in the dimension of time instead of space, things would look different. In its duration, as opposed to its diameter, the Earth demands to be measured on a cosmic scale. At more than four billion years old, it stretches a third of the way across the history of the universe, a third of the way back to the Big Bang itself. Many of the stars you can see on a clear winter’s night are younger than the planet beneath your feet.

Mere persistence is not, in itself, that great a feat. The barren rocks of the Moon have persisted almost as long. But the Earth has not merely endured; it has lived. For almost 90 percent of its history the planet has been inhabited, and shaped by life. The biological mechanisms that first operated in the dawn of life animate the creatures of the Earth to this day, forming an unbroken chain at least 3.8 billion years long.

This unfailing, uninterrupted life demonstrates that the planet is far from fragile. The living Earth is tough on scales it is hard to credit. Life has watched continents crash together and tear themselves apart; skies glowing like bright coals; tropical seas frozen into stillness: it has endured. Slaked in radiation from nearby supernovae, pummeled by asteroids, it has barely faltered and never stopped. Our civilization may be — is — out of balance with its environment; current human ways of life are frighteningly precarious. But to read the fragility of our way of life onto life itself is foolish.

Humans can kill species and diminish ecosystems. Such vandalism poses real dangers to its perpetrators, since human civilization relies on the services some of these ecosystems provide. But at the scale of the planet’s life taken as a whole it is penny-ante stuff. Humanity poses no existential risk to life on Earth, and nor will anything else for hundreds of millions of years. Rich, varied, ever changing — the Earth is all of these. Fragile it is not.

Why so robust? The reason rests in the second great misconception: that the Earth is isolated. This is true only if your sense of connection depends on physical matter moving from place to place. The dust and rocks that rain down from space are indeed the merest spattering, even if some of the larger rocks occasionally cause a little dinosaur-killing discomfort; the traces of gas blown off the top of the atmosphere are truly negligible. Matter trickles in, whispers out. But matter is not everything.

An unending spate of pure luminous energy pours from the Sun in all directions. Eight minutes downstream at the speed of light, part of this extraordinary flux crashes down on the Earth in a 170,000-trillion-watt torrent. Some of it splashes back into space; Major Anders’s “Earthrise” captures that reflected light in the brilliant white of clouds and polar ice. Most, though, is absorbed; this is the energy that drives the winds, makes the waves and currents flow, heats the rocks and warms the sky. The Sun’s energy flows through the earth system and out the other side, ebbing back into the coldness of space as a tide of infrared radiation.

A very small fraction of this energy is caught, not by rock and wind and water, but by life. That fraction of a percent captured by plants and other photosynthetic organisms flows into and through the food webs of the world. It is this sunlight, endlessly refreshed, that allows the grass to grow, the birds to sing — and you to live. The Sun’s energy flows through your breakfast cereal, your morning coffee, your veins and your mind. It animates you as it has animated almost all the Earth’s life for billions of years.

The science of thermodynamics tells us that closed systems tend toward equilibrium, toward dullness, toward entropy. If the Earth were truly as isolated as it looks, that unavoidable tendency would be the lot of life. But the Earth is as open as the sky. Energy from elsewhere floods through it, creating endless chances for complexity and improbability, washing the world’s entropy back into space. The flow of energy that unites almost every living creature on the planet is the same flow that connects our environment to the universe beyond.

For this flow to work, the energy must get out as well as get in. If Major Anders had had a camera working in the infrared, that departing energy would have shown up as a warm glow on the night side of the planet. Forty years on, that glow has dimmed a little; less energy is getting out. By thickening the skies with carbon dioxide, we are blocking the energy’s flow, and allowing a buildup of heat here at the surface of the Earth. This greenhouse warming is small beer in any cosmic sense. It poses no threat to the continuation of life on Earth, but it does pose a threat to tens of millions of people, and will do so for generations to come.

Happily, to see the problem of global warming in terms of this flow of energy is to see its solution. By putting a little of the cosmic energy to use — by developing wind power, appropriate energy crops, hydropower and, most promising of all, solar power — we could do away with the need for that sky-thickening carbon dioxide. Other flows of energy could help too — flows of heat from the depths of the Earth and of radiation bequeathed to us in the uranium of dead stars. But it is solar energy, indirectly or directly, that will dominate the picture, simply because of its abundance. The Sun delivers more energy to the Earth in an hour than humanity uses in a year.

To substitute these flows for the fossil fuels poised to despoil our planet and also run out on us — worst of both worlds — is an epic task. But the message that frames all the other messages of “Earthrise” is that we can rise to epic tasks. Look where the photo was taken. “If we can put a man on the Moon ...” quickly became shorthand for society’s failure to achieve goals that seemed far simpler. But still: we put a man on the Moon, and that does say something. Efforts on a similar scale aimed at harvesting the energy flowing about us are entirely appropriate, and could make things a great deal better. We cannot solve all problems; some climate change is inevitable. But catastrophe is not.

“Earthrise” showed us where we are, what we can do and what we share. It showed us who we are, together; the people of a tough, long-lasting world, shot through with the light of a continuous creation.

Oliver Morton, the author of “Mapping Mars: Science, Imagination and the Birth of a World,” and, most recently, “Eating the Sun: How Plants Power the Planet,” is the chief news and features editor of the journal Nature.