India, Jan. 11 -- A popular suggestion for an alternative biochemistry is one based on silicon rather than carbon

Life is pretty easy to recognise. It moves, it grows, it eats, it excretes, it reproduces. Simple. In biology, researchers often use the acronym " MRSGREN " to describe it. It stands for movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

But Helen Sharman, Britain's first astronaut and a chemist at Imperial College London, recently said that alien lifeforms that are impossible to spot may be living among us . How could that be possible?

While life may be easy to recognise, it's actually notoriously difficult to define and has had scientists and philosophers in debate for centuries - if not mi...