Is Alien Life Falling From The Sky?

David Hambling reports on the meteorite that struck Peru last year, and how local villagers then succumbed to a mystery illness. The idea that microbial alien - and potentially infectious - life is falling from space may sound bizarre but is championed by some scientists (read Flipside 28 to find out the truth behind the Peru impact).

Panspermia is the belief that 'seeds' of life exist throughout the universe, and that these develop wherever they can find the right environment. Not many scientists accept the theory, but it has had some notable supporters. These include astronomers Sir Fred Hoyle and Prof Chandra Wickramasinghe.

There are several types of arguments in favour of panspermia. One is based on statistics. There is a more chance of life originating from one source in the universe and spreading out than there would be of it developing on millions of different planets.

Panspermia supporters also point to fossil evidence that life on Earth appeared at least 3.5 billion years ago, almost as soon as the planet cooled down. This suggests that seeds of life were already there and waiting for the right conditions.

There is also an increasing amount of research on extremophiles, bacteria and other creatures that can survive in conditions which were thought be impossible. The Apollo 12 mission to the Moon recovered samples from an unmanned lander that had touched down three years earlier. NASA was surprised to find some bacteria had apparently survived unprotected within the mechanism all that time.

Astronomers have confirmed that clouds of many carbon compounds exist in interstellar space. In 1994 amino acids, the 'building blocks of life' were detected in a nebula called Sagittarius B2. It's possible that these could accumulate on dust particles and react with each other to produce larger and more complex molecules. However, nobody has shown that life could develop this way.

Historical evidence comes from the way that comets have always been linked with epidemics, such as the 1665 plague in London. In 2003 Professor Wickramasinghe claimed that the SARS virus was so different from any existing viruses on Earth that it must have come from somewhere else. However, most scientists still insist that SARS was an evolution of another flu-like virus. Rather than outer space, they think it came from civet cats.

The argument continues, but the Panspermia theory can only really be proven by space probes bringing back samples of extra-terrestrial life.