Astrobiologist Dr Monica Grady Monica - The focus of my work is investigating life on Mars to find out whether it's there. There are other questions we also hope to answer: would life on Mars be the same as that
Chris - Do you think that the fossils found in meteorites from Mars might have been the start of life on Earth?
Monica - The fossils found in the meteorite were tiny and a huge amount of discussion has come out of it! What's more, only one such meteorite has been found. It is now thought not to be a fossil from Mars, but that is not very important. We know a lot of other things about Mars and it is this other evidence that leads us to think that Mars might have had life on it.
Chris - Could a life-form survive the journey from Mars to Earth?
Monica - Life would certainly perish if it floated by itself as it would be destroyed by the radiation of space. However, if it were buried under a small crust of ice or rock, it would be safe. A spore or something similar could have made it to Earth in this way and have been safe for hundreds of thousands of years. My gut feeling is that it didn't happen like this at all. I think life would have started on Earth and Mars separately.
Life started from chemistry and we know from looking at Earth the type of ingredients needed. These include carbon, water and a way of getting them together. There must be some stable platform for the building blocks to fit together on and some sort of protection from radiation, heat and pressure. This protection comes in the form of an atmosphere like we have on Earth, something found in few places elsewhere in the solar system. Mars had an atmosphere at one point but lost it. This is why we think there might have been life on Mars some time in the past. It could still be lurking somewhere beneath the surface.
Chris - What are the signs of life? What hallmarks can be used to pin point it?
Monica - The most important thing is that life metabolises: it breathes in, converts and breathes out again. During this conversion trace elements are produced, so when looking for life we look for trace gases...