Science has learned a lot about life on Earth, but still hasn’t figured out exactly how it got started. There are lots of theories, but none have been proven; in fact, the one that held sway the longest—the so-called “primordial soup” theory that life emerged from a mixture of organic molecules in the ancient ocean—has been disproved. Nobody knows precisely how our planet changed from lifeless rocks and water to the stage for the drama of life.
Among the many theories is one that is intriguing to some scientists, but very annoying to others. It’s called “Panspermia”—the theory that life first arrived on Earth from outer space. Not on spaceships, of course, but as microbes that hitched rides on meteors.
Okay, this idea has probably launched your skepticism meter deep into the red zone, and you have plenty of company there. However, panspermia may not be as outlandish as it seems on first encounter.
Scientific evidence indicates that life appeared on Earth between 3.8 and 4 billion years ago. But, that amazing development apparently overlapped with another long-lasting situation called “the heavy bombardment”, i.e. a downpour of meteors that treated our young planet like bullies treat a nerd.
Some scientists theorize that any emerging life would have been destroyed because meteors play very rough. For example, consider the single meteor that wiped out the dinosaurs (long after the heavy bombardment). This flying mountain, the size of Everest, smashed into our planet at about 1,700 mph; that’s the speed of an average bullet. Plunging from the cruising altitude of a 747 to the ground in about 0.3 seconds, it briefly made the Earth’s surface hotter than the sun, according to Peter Brannen’s book, “The Ends of the World.” One big meteor=0 dinosaurs.
How, then, could any microscopic life that might have been around 4 billion years ago have survived “the heavy bombardment”? Enter the Panspermia theorists, bearing a heavy load of irony. They suspect that the meteors that gradually carpet-bombed Earth were carrying payloads of bacterial spores from elsewhere—perhaps even several “elsewheres”.
The theory is that spores that somehow became attached to meteors could theoretically survive long interplanetary journeys. Scientists have found that these microscopic tough guys enter a kind of suspended animation when deprived of nutrients. But once they land somewhere with food, they wake up and chow down. Now, bacterial spores can indeed die, but like teeny-tiny Clint Eastwood characters, they’re hard to kill.
For example, scientists have done experiments that have shown that spores from a certain ocean algae, Nannochloropsis oculata, just might be able to survive a ride on a crashing meteor. First, they made some rock-and-ice pellets loaded with the algae. Then, they fired the pellets into water at four miles per second, the average velocity of a crashing meteor. Surprise! Some of the spores survived.
A different study tested the durability of spores from Bacillus subtilis, a bacteria found in soil. The scientists discovered that these little guys could survive in outer space, if they were shielded from ultraviolet radiation—as they would be inside a meteor. Now, the study didn’t run the length of time it would take for a meteor to travel from “elsewhere” to Earth, but some of the spores did survive for up to six years.
As interesting as these results may be, they are far from proof of the Panspermia Theory. For that to happen, we’d have to find life on another planet, and figure out how bacterial spores from there hitched a meteoric ride here. Even if we were to pull that off, we’d only succeed in moving, not answering, the big question: how in the world, or out of it, did lifeless matter become life that matters?