From The New Yorker:
There once were two planets, new to the and inexperienced in life. Like fraternal twins, they were born at the same time, about four and a half billion years ago, and took roughly the same shape. Both were blistered with volcanoes and etched with watercourses; both circled the same yellow dwarf star—close enough to be warmed by it, but not so close as to be blasted to a cinder. Had an alien astronomer swivelled his telescope toward them in those days, he might have found them equally promising—nurseries in the making. They were large enough to hold their gases close, swaddling themselves in atmosphere; small enough to stay solid, never swelling into gaseous giants. They were “Goldilocks planets,” our own astronomers would say: just right for life. The rest is prehistory. On Earth, the volcanoes filled the air with water vapor and carbon dioxide. The surface cooled, a crust formed, and oceans condensed upon it. In hot springs and undersea vents, simple carbon compounds bubbled up to form amino acids and peptides. The first bacteria moved through the ooze; then came blue-green algae, spreading across the planet like a watery carpet, drinking in sunlight and exhaling oxygen, giving breath to everything that came after. Geologists call this the Great Oxygenation Event—the most momentous change in the planet’s history. It seems inevitable now: life’s triumphant march toward complexity, toward us. But like most creation stories this one is also a cautionary tale. It has both a Heaven and a Hell.
In 1877, when the Italian astronomer Giovanni Schiaparelli drew the first detailed map of Mars, he imagined the planet as an earthly paradise. He labelled one region Eden, another Elysium, others, on later maps, Arcadia and Utopia. Peering through his telescope on the roof of the Palazzo di Brera, in Milan, Schiaparelli had seen what looked like oceans, continents, and water channels swim into view. “The planet is not a desert of arid rocks,” he wrote. “It lives.” And his successors often took him at his word: the sharper their telescopes, the blurrier their vision. They saw mountains of ice and rivers of snowmelt, William Sheehan writes in his 1996 book, “The Planet Mars: A History of Observation and Discovery.” They saw fertile oases and a moss-green equator. They saw an irrigation system so linear and “trigonometric,” as the astronomer Percival Lowell put it, that it could only be the work of a highly intelligent race. Some even saw a Hebrew word for Almighty—Shajdai—spelled out on the planet’s surface. “True, the magnitude of the work of cutting the canals into the shape of the name of God is at first thought appalling,” the San Francisco Chronicle noted in 1895. “But there are terrestrial works which to us today seem no less impossible.”