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170517 Searching for Early Life on Earth and Mars - Malcolm Walter

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Published on Jun 1, 2017

The earliest recorded life on Earth was microbial: bacteria and their cousins the archaea. It has taken at least 50 years of research to arrive at convincing interpretations of the evidence because such tiny organisms, which lack hard parts, do not survive well through time.

It has been a long hard job with numerous debates and disputes, some fiery. Out of this cauldron has emerged a rich record of early life, best documented in the Pilbara region of Western Australia.

We now have a record extending back 3.5 billion years, with some hints back to 3.7 billion. The record is still meagre because it is known only from the Pilbara and a small part of South Africa, and possibly Greenland. The problem is that the further we look back in time the fewer rocks there are where the signature of past life can still be seen.

Most of the ancient rocks have been tectonically recycled, as for example in plate tectonics. Our planet is 4.56 billion years old but there are essentially no rocks older than 4.0 billion.

That last point is one of the reasons to search for early life on Mars: there has been little or no plate tectonics there and the ancient rock record seems to be well preserved. There is another overarching reason to search for life on Mars – did life arise more than once in the Universe? This must be one of the greatest enigmas in science and philosophy.

The Pilbara has become the key “analogue” region for developing exploration strategies in the search for life on Mars. Over the last two decades or so there has been intense international interest in the Pilbara, with research projects based in NASA, the European Space Agency and elsewhere.

My colleagues and I are working now to gain World Heritage listing for the key fossil area of the Pilbara.

Australia plays a key role in this sort of research for another reason. Shark Bay on the coast of Western Australia hosts a “window on the past”, with living microbial structures called stromatolites. These have been studied intensively for many years and now are central in efforts to understand the biology of their ancient counterparts, in the Pilbara and elsewhere. For this and other reasons Shark Bay is now a Marine National Park and a World Heritage area.

The future lies in more missions to Mars. So far all missions have been one way, but plans are underway for a “sample-return” mission, and sometime this century there will be astronauts on Mars. It is inevitable: by nature, we are explorers.

Professor Malcolm Walter was awarded an Order of Australia in the 2017 Australia Day Honours for his significant service to science in the field of astrobiology as an author, academic, educator and mentor.

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