Watching Prometheus, the science-fiction film by Ridley Scott, with my son the other day got me to thinking about panspermia. This is the idea that life sometimes spreads through the universe by riding on interstellar flotsam and jetsam like meteors or asteroids.
Maybe a life-bearing planet blows up and some of the chunks have spores or at the very least a few building blocks of life. One of these chunks travels for centuries or millennia (or probably even longer) until it hits a lifeless planet where the spores come to life. Soon the planet is teeming with life.
This isn’t exactly what happened in Prometheus. At the start of the movie, a humanoid alien disintegrates itself so that it can unleash its DNA into the waters of a lifeless Earth. The DNA then starts dividing and/or mutating, eventually resulting in all the life on Earth.
Well, I assume it is mutating. Otherwise it would be very strange for all life to come from humanoid DNA. Although I suppose the alien could have been a colony of different organisms that were then all released into Earth’s lifeless oceans. Or maybe all the alien’s skin and intestinal bacteria were also released so they could spread throughout the Earth. Or any other of a number of possibilities.
Technically, though, this isn’t really panspermia. It is more akin to something called exogenesis. In panspermia, the spread of life is accidental. It is deliberate with exogenesis.
I am a sucker for science-fiction movies like Prometheus. I love the thought of being able to find and confront our extraterrestrial ancestors like ancient Greeks storming Mount Olympus.
Unfortunately there isn’t any good evidence that life on this planet came from another planet. But there are hints that the start of life on Earth may have been aided by space borne organic molecules.
Scientists have found some very life like molecules on meteorites. For example, one meteorite is reported to have had uracil, a key component of RNA, as well as a number of other DNA-like bases.
These probably didn’t come from planets that had life though. Instead they were created through some run-of-the-mill ammonium cyanide chemistry out in space. It may be that organic molecules are more easily created in space than they were on the Earth of four billion years ago. Or even that they are much easier to make than scientists previously thought.
So these organic molecules from space might have provided some of the raw materials from which life arose rather than being proof of life elsewhere. Instead of an alien disintegrating so it could release its DNA, maybe lots of meteorites disintegrated and released their organic molecules to give life a jump-start.
This is way more satisfying to me than panspermia or exogenesis. With either of these, we are just pushing the problem of the start of life back a step. Life had to evolve on those other planets at some point (or at least at a single planet somewhere) so panspermia doesn’t really answer the biggest question—where did we come from. It just rephrases the question to how did our extraterrestrial ancestors evolve.
Richard Dawkins on organic molecules from space