Did asteroids bring life to Earth?

Nick Spall examines the evidence that life on Earth came from outer space – and how close science is to proving it

- 

We humans are always wondering whether we're alone in the Universe.

But what if we are one of a long line of species that were around long before our planet even existed? This intriguing idea, that life didn't originate on Earth but arrived from elsewhere in the Galaxy, has always been controversial, but it's one that keeps resurfacing. In fact, it's only gaining credence as we uncover more potential signs of life on other planets. If we do find proof that life exists elsewhere, the question that then arises is: did that life evolve separately on each planet, or did it travel there from an earlier source? And if we can entertain the idea that that could have happened elsewhere, why not on Earth?

The 'panspermia' theory asserts that the building blocks of life, or even life itself, were delivered to Earth by piggybacking on a comet or asteroid, kickstarting the evolutionary process that culminates in life existing and, ultimately, you reading this article. It's an idea that's had much derision in the past, so why do so many serious scientists still entertain it as possible fact? What makes it so attractive? Let's have a look at the evidence that supports it...

Organics everywhere

The panspermia theory isn't new. Over 50 years ago, the work of the late Sir Fred Hoyle and Chandra Wickramasinghe argued that microbial life permeates the Galaxy on a vast cosmic scale. Their hypothesis, extending the thinking of 19th-century scientists, including Lord Kelvin and Svante Arrhenius, was that life may be distributed from world to world by meteors, asteroids, dust and comets.