3. Universal biology
All living things on Earth are built from the same ingredients. From humans to moulds to humpback whales, we all consist of the same organic compounds – the same raw materials. But why shouldn’t life elsewhere in the cosmos be built from something else? From silicon, which has similar properties to our own carbon, or from titanium perhaps?

Well, although it was once fashionable, that idea is now losing ground. There is reason to believe that the materials of life are universal and inevitable, and produced as a by-product of cosmic processes. These materials are in meteorites, comets and even in interstellar space.

Nasa astrobiologist Lynn Rothschild explains: ‘There is a big overlap between these compounds found in interstellar space and what you would find if we took an earthworm and ground it up. Things like amino acids and the components that go into making nucleic acids. Things like DNA, which really defines life on Earth.’ All this leads scientists to suspect that life on other planets would have started from the very same chemicals as life on Earth did.

Indeed, there is tantalising evidence to suggest that life may be present on Mars. Gases that indicate the presence of living things have turned up in the Martian atmosphere. SETI scientist Seth Shostak can barely hide his excitement: ‘This methane is indicating to us that underneath that dreary, sterile surface, there are some bacteria living there. And that would tell you right away, hey, the next planet out also had biology. Biology is just really common place.’

Life on Mars would indeed suggest that life is everywhere.

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