The young scholar clutches the book to his chest as he works his way through the crowd. Campo dei Fiori is packed; it's a jubilee year, and Rome teems with pilgrims, beggars, and pickpockets. He edges forward, brushing aside the vendors who tug at his sleeve. Days earlier, a small item in a local broadsheet caught his eye. A Dominican monk from Nola was to be put to death, having exhausted the patience and goodwill of the authorities. The scholar sighs. His heart is heavy at the prospect. It is not yet a century since the death of Leonardo, but enlightenment has dimmed so much that it seems like eons.

With difficulty, the scholar climbs scaffolding behind a merchant stall so he can see over the heads of the mob. Yelling at the far side of the square tells him that Bruno has arrived, having been paraded naked through the streets of Rome. He is bound to the stake with thick rope while a local functionary reads the charges. The scholar can only catch fragments: “impenitent heretic … failure to recant … persistent follies.”

If Earth's future space travelers came to this place, they would declare it a godforsaken wilderness. A trackless vista of cliffs and escarpments stretches to the horizon. Brown rock scorches under twin giant suns in a blood-red sky. The air is a thin gruel of sulfur dioxide, methane, and nitrogen. But there's more here than meets the eye. In the pore space of the rocks, something is stirring.

At a boundary layer with the deep mantle, mildly acidic water bubbles through the rock, driven by heat and pressure from the interior. Miles underground, microbes thrive in a rich brew of organics and dissolved minerals. They move by sensing magnetic fields and temperature gradients. Huge colonies begin to differentiate their functions and metabolisms to better use the available resources. Symbiotic behavior emerges.

In the course of ceaseless and random genetic variation, some organisms develop the ability to vibrate their outer membranes and sense when it is perturbed. The timing of a return ultrasound wave acts as a primitive proximity sensor. This brand of microbes maintains the spacing to garner more resources, so it rapidly dominates the colony.

As the strategy becomes more successful, the organisms with the most powerful emission or most sensitive reception must deal with a cacophony of ultrasound signals.

In the dream, you are in an ice cave. It is starkly beautiful, suffused in blue light from an outside source. There's nothing to eat, no sustenance, just the angular planes of ice crystals. It is stunningly cold, well below freezing. Your breath billows in front of you; perspiration forms a frozen rind on your neck. You can't stay here long. Then you notice creatures working industriously along the far wall of the cave. They're oblivious to the intense cold. From the strange smell, you guess that they have antifreeze running through their veins. This place is clearly their home.

Then you awake—not to your bed but to another strange world. You are on the shores of a river, with canyon walls that rise up and disappear in the gloom. The river is acrid and filled with the worst kind of industrial effluent. The water is so acidic that it sizzles as it passes over the rocks, which are themselves discolored by chemical residue. The smell is foul and metallic, and it almost makes you gag.

Her feet crunch into the red crust. She hops tentatively, testing the feel of one-third gravity. Then a second hop, higher and more playful. Nice. Looking back she sees her spacecraft resting in a shallow depression. Squat and small, it looks like a toy. A shadow of anxiety crosses her mind. With all the trade-offs, cuts to NASA, the needs of national security, it was this or nothing: a single person sent to Mars to bring back samples. A robotic clone of her spacecraft stands ready for launch, but she knows the odds of a successful rescue are long. She's one hundred times farther from Earth than anyone in history. Utterly alone.

Yet there is nowhere else she would rather be. The geologist gets to work. Her trained eye scans the alluvial plain and settles on one particular outcropping. She moves toward it in an awkward loping motion. It's difficult to judge distances through the thin atmosphere laced with dust, where ochre rocks shade into an apricot sky. An hour later, she is there, with only the sound of her breathing for company. Along one slope of the outcropping, a raised seam, split like a wound, exposes the layers below. Perfect.

The year is 2067. Earth has survived, its environment battered and bruised, and humans have muddled through, their few shining moments eclipsed by tribal squabbles over resources and religion. Many diseases have been conquered, but others have risen to take their places. The evolutionary struggle between men and microbes is at a stalemate. In an era of quantum computing, bodies of people in the western world are patrolled and retooled by medical microbots. Embedded intelligent agents ceaselessly draw on the vast web of information that permeates the air.

It was one hundred years into the space age before humans cracked the problem of interstellar travel. Fusion drives now power all major commercial aircraft, and larger craft service tourism and mining outposts throughout the Solar System. Astronomers have honed their techniques and routinely detect terrestrial planets as small as Mercury. Robot emissaries traveling at half light speed have fanned out to hundreds of the nearest stars, and a few Earth “cousins” are known.

Twenty years earlier, in 2047, one hundred people set out on a momentous journey. Fueled by the same urge that sent humans migrating across continents tens of thousands of years before, and demoralized by the loss of vision and the spiritual decay on Earth, they were the first to cut the umbilical cord and attempt to homestead a new planet.

The travelers look out onto the shore of a strange and hostile world. They don't leave the spacecraft; a probe shows that the atmosphere is mostly nitrogen, with smaller but lethal amounts of sulfur dioxide and methane and a hint of ammonia. Volcanoes belch gases into the sky, and the spacecraft trembles every few minutes from seismic activity. A young star, orange and bloated, perches on the horizon.

It's a young planet. The newly minted crust is still warm and plastic. Oceans have recently condensed from steam and are still kept warm and turgid by geothermal energy. Samples drilled from the crust show an age of two hundred million years—only 2 percent of cosmic time and the same fraction of the time the star will provide warmth to this planet.

Working swiftly, the visitors wrap up their experiments. It's not safe here. This soon after its formation, the planetary system is still strewn with debris. Every hour or so, the spacecraft shudders as a meteor slams into the ground nearby. There's a continuous light show overhead as smaller fragments burn up in the atmosphere. The large moon looming in the sky, which was splashed off an earlier impact, is a reminder of the potential for devastation.

It's quite peculiar to be human. Our lives are filled with event and episode, with work and recreation, with the ebb and flow of friends and family. Seen from above, our actions would seem as purposeful as the activity of bees in a hive or squirrels in a forest. Yet we each house the awareness that we're living, conscious entities. We reflect on our existence. We know that we will die. Perhaps we share self-awareness with a few other species on Earth, but no other creature has gained knowledge of its place in the largest landscapes of time and space.

The history of astronomy has been a steady march of awe and ignominy: awe at the prodigious size and age of a universe with tens of billions of galaxies, ignominy that we have no special place among those galaxies and their countless trillions of stars. Stars and nebulae and planets are the result of natural forces. Rocks and clouds weren't created for our pleasure or benefit. The last bastion of specialness is our existence. Surely life has purpose and meaning. As the poet Stephen Crane has written,

The final step in the Copernican revolution would be the revelation that we live in a biological universe.