Signs Of Life From 3.5-Billion-Year-Old Hot Springs Could Change Mars Mission Target

Geysers like this one in Iceland produce hot springs, and 3.48 billion years ago life was thriving in similar versions. Tara Djokic

The discovery of life around 3.48 billion-year-old hot springs in the Pilbara region of Western Australia could influence debate on where life first appeared on Earth. The news could also affect our choices about the best place to look for life on Mars.

Darwin proposed that life began in “warm little pond”, but in recent years the locations that most resembled this – the outskirts of volcanic hot springs on land – have been displaced as favorites by hydrothermal vents on the ocean floor. A conclusion between these competing theories would shape our choices about where to look for life beyond the Earth. Mars once had its own hot springs, while Europa and Enceladus are thought to have hydrothermal vents today.

The hot springs theory has been bedeviled by the fact that the oldest evidence we have for life at such springs was 400 million years old – yet we know from molecular clocks and marine fossils that life is at least 4 billion years old. Moreover, while plants and animals didn't make it onto the land until far more recently, microbes have been found in terrestrial locations dating back 2.7-2.9 billion years. Yet even this was considered puzzlingly recent if life's origins were at sites surrounded by land. It would be far more understandable if life took more than a billion years to get out of the oceans, than if it moved from on land pools.

So the announcement, by University of New South Wales PhD student Tara Djokic, that unambiguously terrestrial rocks almost 3.5 billion years old contain signs of life, shifts the debate. Djokic stressed to IFLScience that her discovery does not prove life began in hot springs, but it does remove arguments against that idea.

We may never be able to conclusively establish life's place of origin on Earth, but space is a different matter. All missions to Mars have been motivated in part by hopes of finding life, but the Mars 2020 rover aims to seek more directly. The list of possible locations for this mission has been slowly shortening and Djokic points out that of the three remaining locations, one – Columbia Hills, where Spirit landed – appears to contain the remnants of a hot spring

A modern hot spring. The colored areas indicate the presence of various sorts of life.

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