Understanding the context of early life from the evidence on Earth is difficult. Because the Earth's crust is so active, there is very little surface rock remaining from the time when life originated, before 3.5 billion years ago. "There are only two places on Earth where rocks formed at that time are relatively well preserved," says Tanja Zegers, a geoscientist from Utrecht University in the Netherlands. These are at Pilbara in Australia and Kaapvaal in South Africa.
The pillow basalts at Pilbara provide strong evidence that there was liquid water on Earth at that time, because their shape could only have developed underwater. Liquid water is crucial for life. But, says Zegers, understanding the origin of life from this evidence is a bit like trying to piece together western civilisation from Asterix and Obelix cartoons.
On Mars, by contrast, about 50% of the surface is from before 3.7 billion years ago, so there is a lot more to work with. "Mars may be our best bet to find out about life's origins on Earth," says Zegers.
At the time life was evolving on Earth, it seems there was liquid water on Mars too, and a similar environment in many respects. The oldest areas on Mars have hydrated minerals, like clays, which contain water within the mineral structure. They also show signs of surface flows like river networks. But about 3.8 billion years ago, the Martian atmosphere declined and the planet went into a deep freeze. Now, atmospheric pressure on Mars is too low for water to exist as a liquid at all.
Understand habitability on Mars and early Earth requires focused geological research. Several missions to Mars, to map the planet and eventually bring
|Contact: Gnter Von Kiedrowski|
European Science Foundation