Might There be Life on Mars?
All life as we know it requires liquid water, hence the strong interest in finding evidence of past liquid water on Mars, and understanding the history of this water. There is strong scientific evidence that liquid water once occurred on the surface of Mars, so it is possible that life could have become established. The first evidence for life on Earth, in the form of fossil bacteria, occurs about 3.5 billion years ago — the time that the Martian environment was changing from warmer and wetter to colder and drier. Microbial life on Earth probably existed before this time period, possibly becoming established after the period of intense asteroid bombardment was over, but there is no record of it. In short, it took life up to a billion years to become established on Earth, and this may be a reasonable timeline for Mars, as well. Given this start, and using Earth as a model, conditions on much of Mars would have been suitable for life for about a half billion years, before the climate det
