Extra-terrestrial life is the existence of life outside of the
Earth. Are we alone in the universe? So far the only life we
know about inhabits our planet – Earth – but there are planets
that orbit other stars in a similar way to how the Earth orbits
the Sun. This activity could form a class discussion, and could
either be done in the context of the whole planet, or at
organism level. Or you could concentrate on one of the questions
on the student page, such as 'How could we recognise that life
on other planets was intelligent?' If looking at the planet as a
whole - using the Gaia theory - think about the types of
"signatures" that have been left on our planets due to the
presence of life. The search for life on Mars is focused on
evidence for liquid water on the planet or its presence in the
past. One way of doing this is by looking at the patterns of
valleys and mountain-like features on the planet's surface and
trying to work out if they may have been formed by flowing
water. Scientists also look for certa