Evidence is “steadily mounting� that life on Earth began elsewhere in the Universe and was brought here by comets, according to a new paper by Professor Chandra Wickramasinghe.

Professor Wickramasinghe, Director of the Cardiff Centre for Astrobiology, says that a clear pronouncement on the matter is now “overdue�.

In his paper, published in the International Journal of Astrobiology this month, Professor Wickramasinghe assesses the case that life had a cosmic origin in the light of astronomical discoveries of the past 30 years.

He argues that astronomy shows organic molecules and organic dust are available on a huge scale, with a third of interstellar carbon in this form. He claims it is likely that a large amount of this material comes from decayed biological organisms, as is the case on Earth.

Professor Wickramasinghe concludes that the evidence of the past 30 years strengthens the case that life first came to Earth from impacting comets carrying organic matter around 3.8bn years ago.

However he argues that “cultural barriers� still exist to admitting the connection. In the paper, he says: “As we enter a new decade £“ the year 2010 £“ a clear pronouncement of our likely alien ancestry and of the existence of extraterrestrial life on a cosmic scale would seem to be overdue.�