A short history of nearly everything - Bill Bryson [144]
Life emerged so swiftly, in fact, that some authorities think it must have had help—perhaps a good deal of help. The idea that earthly life might have arrived from space has a surprisingly long and even occasionally distinguished history. The great Lord Kelvin himself raised the possibility as long ago as 1871 at a meeting of the British Association for the Advancement of Science when he suggested that “the germs of life might have been brought to the earth by some meteorite.” But it remained little more than a fringe notion until one Sunday in September 1969 when tens of thousands of Australians were startled by a series of sonic booms and the sight of a fireball streaking from east to west across the sky. The fireball made a strange crackling sound as it passed and left behind a smell that some likened to methylated spirits and others described as just awful.
The fireball exploded above Murchison, a town of six hundred people in the Goulburn Valley north of Melbourne, and came raining down in chunks, some weighing up to twelve pounds. Fortunately, no one was hurt. The meteorite was of a rare type known as a carbonaceous chondrite, and the townspeople helpfully collected and brought in some two hundred pounds of it. The timing could hardly have been better. Less than two months earlier, the Apollo 11 astronauts had returned to Earth with a bag full of lunar rocks, so labs throughout the world were geared up—indeed clamoring—for rocks of extraterrestrial origin.
The Murchison meteorite was found to be 4.5 billion years old, and it was studded with amino acids—seventy-four types in all, eight of which are involved in the formation of earthly proteins. In late 2001, more than thirty years after it crashed, a team at the Ames Research Center in California announced that the Murchison rock also contained complex strings of sugars called polyols, which had not been found off the Earth before.
A few other carbonaceous chondrites have strayed into Earth's path since—one that landed near Tagish Lake in Canada's Yukon in January 2000 was seen over large parts of North America—and they have likewise confirmed that the universe is actually rich in organic compounds. Halley's comet, it is now thought, is about 25 percent organic molecules. Get enough of those crashing into a suitable place—Earth, for instance—and you have the basic elements you need for life.
There are two problems with notions of panspermia, as extraterrestrial theories are known. The first is that it doesn't answer any questions about how life arose, but merely moves responsibility for it elsewhere. The other is that panspermia sometimes excites even the most respectable adherents to levels of speculation that can be safely called imprudent. Francis Crick, codiscoverer of the structure of DNA, and his colleague Leslie Orgel have suggested that Earth was “deliberately seeded with life by intelligent aliens,” an idea that Gribbin calls “at the very fringe of scientific respectability”—or, put another way, a notion that would be considered wildly lunatic if not voiced by a Nobel laureate. Fred Hoyle and his colleague Chandra Wickramasinghe further eroded enthusiasm for panspermia by suggesting that outer space brought us not only life but also many diseases such as flu and bubonic plague, ideas that were easily disproved by biochemists. Hoyle—and it seems necessary to insert a reminder here that he was one of the great scientific minds of the twentieth century—also once suggested, as mentioned earlier, that our noses evolved with the nostrils underneath as a way of keeping cosmic pathogens from falling into them as they drifted down from space.
Whatever prompted life to begin, it happened just once. That is the most extraordinary fact in biology, perhaps the most extraordinary fact we know. Everything that has ever lived, plant or animal, dates its beginnings from the same primordial twitch. At some point in an unimaginably distant past some