Dr Monica Grady is a mineralogist at the Natural History Museum. Dr Grady is an expert on meteorites and what makes the Earth special as a planet that supports life.

What are the special properties of the Earth that make life possible? How likely is it that other planets have these properties?
The Earth is special in all of its properties – plate tectonics, the atmosphere, magnetic fields and so on. There are other possibilities in our own solar system – Venus just a bit closer to the Sun than the Earth, and Mars just that little bit further out. But both those planets don’t seem to have any intelligent life on, or at least none that’s been in touch with us. Part of the reason is that these planets have taken different evolutionary pathways.

Mars is half the size of the Earth, it has cooled more quickly than the Earth, it presumably has a solid core, it doesn’t have this activity called plate tectonics, it’s lost its atmosphere, it has a sterile surface, it’s cold, it’s barren, it’s dry. Venus on the other hand is much hotter than the Earth, it’s been very active in terms of volcanic activity, in terms of molten rocks on the surface. So huge amounts of CO2 have been put out on this planet, which is the same size as the Earth, but it has a much, much thicker atmosphere because the CO2 couldn’t be taken away again, because it doesn’t have plate tectonics. I think it is unlikely that we’re going to find just the right sort of planet orbiting just the right sort of star beyond our own solar system, perhaps even beyond our own galaxy.

What are the conditions required for intelligent life to evolve?
We could perhaps regard the emergence of life as an inevitable consequence of physics and chemistry - you get the right ingredients, you get the right conditions, you get life. Whether that life is intelligent is a completely different matter. We’ve got billions of years of evolution, going from single cells on the Earth to intelligent life, but that hasn’t been a progressive evolution, there have been fits and starts, there have been great periods of evolution and then a break.

One of the biggest breaks happened 65 million years ago when a meteorite impacted the Earth and wiped out most species. At that particular time the dominant species, the dinosaurs, were wiped out and a very unimportant species, little furry mammals then were able to come to prominence. Without that impact perhaps intelligent life might not have emerged on the Earth, or it might be completely different. So we can’t just regard evolution, we need to think of these other things that have happened, these chance events as well as the general evolutionary sequence.

Why are we so obsessed about the idea of the existence of other intelligent life? What do you think we would learn about ourselves if we were to make contact?
Ever since the dawn of time people have looked up at the sky and seen the stars and wondered what’s out there – is there anything, is there anybody else out there? I think it’s a primitive, a primeval urge, perhaps ‘homo sapiens the conqueror’ - we like to think that we’re in charge. Perhaps we are worried that there’s something more intelligent than us out there, perhaps our instincts are more territorial and defensive. I hope not, I hope that if we do find intelligent life out there, life which is more intelligent than we are, I hope we’re open enough to be able to accept that and to be able to learn from them. I think that will be terrifically humbling though and I think it would destroy humanity’s ego to find that we’re not the top of the tree, that we are much more a lowly species than we like to think. But I hope that if that is the case then we have the humility to accept that and to learn.

What kind of ‘intelligence’ do you think we are likely to encounter if we do make contact with an extra-terrestrial being?
One of the problems with trying to define and understand ‘intelligence’ is that we only look at our own patterns of behaviour. It’s possible that there are different types of intelligences that we don’t understand, that we don’t appreciate, something which is so completely beyond our ken that that we wouldn’t even recognise it as intelligence when we see it. Ant colonies, bee colonies have a certain amount of intelligence, we perhaps say, ok, they’re intelligent in one way but not in another. I think this is where research on computers and computer networks and neural networks is going to help to try to understand actually what makes us tick and what makes us intelligent, then to help us carry that forward to looking for intelligence elsewhere.

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