Guest Post: Building a habitable planet

337039main_pg26_as07-08-1933_small crop
NASA

‘How to build a habitable planet’ is the title of a popular American college textbook which tells the story of the Earth from ‘The big bang to humankind’. It’s a big book – because it is a long story. All the evidence we have suggests that in its infancy the Earth was a most inhospitable planet and not very different from its near neighbours. Back then it had a transient volcanic landscape, a carbon-dioxide-rich greenhouse atmosphere and was periodically bombarded with asteroids from space. In contrast today we see a planet with mobile tectonic plates, oceans, continents, an oxygenic atmosphere and teeming with life, fundamentally different from Mercury, Mars or Venus. So, why? What is it about the history of the Earth which makes it so different now from its near neighbours? Continue reading

Guest Post: Life on Mars – revisited

Martian rover (NASA) crop
NASA

Are we alone in the Universe? This question has teased scientists and philosophers for many decades and is a central theme in much science fiction writing. More recently, as planets have been discovered in solar systems other than our own, the question has returned. Could there be another Earth-like planet colonised by living organisms out there somewhere? This field has become so important scientifically that it is now regarded as a separate discipline – that of astrobiology. Continue reading