Letter: Martian microbe in the soup

Sir: N C Wickramasinghe (letter, 20 August) claims that the discovery of microbial forms in the Arctic Martian meteorite vindicates panspermia, and rules out the Earth-centred primordial soup.

With respect to him, this is not so. In chapter 15 of Carl Sagan and Iosef Shmuelovich Shklovskii's work Intelligent Life in the Universe, the essential difficulty for the panspermia hypothesis is identified. If the pressure of sunlight on a biological particle is sufficient to exceed the force of gravity and drive the particle away from its own star, it will drive it away from any similar star, and hence the particle may never come to rest in a compatible environment.

This difficulty does not apply to a particle travelling the relatively short distance from the Earth to Mars. The particles in the meteorite are therefore most easily explained as the descendants of particles thrown from the Earth's own primordial atmosphere and in consequence as being the earliest known record of pollution.

Belief in the uniqueness of life on Earth flies in the face of all the speculative reasoning of 20th century science. However, the meteorite adds nothing to that speculation, and those who doubt can still, without shame, await proof.

R G WILLIAMS

Lindfield, Sussex