The image shows the finely laminated horizon from where the materials studied herein were sampled © Frances Westall

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Earth’s oldest stromatolites help in the search for ancient life on Mars

Ancient rocks from Western Australia are being used to guide scientists to the samples on Mars that are most likely to hold signs of past life.

Ancient rocks from Western Australia are being used to guide scientists to the samples on Mars that are most likely to hold signs of past life. 

By understanding the morphologies and microstructures of these stromatolites, scientists will be better equipped to identify similar samples on the Martian surface that might also once have held signs of life. 

The origins of ancient stromatolites have long been debated by the geological community with some believing they are formed from chemical reactions between the rock and the environment, and others proposing it is a biological process. A new paper led by Dr Keyron Hickman Lewis of the Natural History Museum released in the journal Geology uses a range of high-resolution analytical techniques to establish the biological origins of Earth’s oldest stromatolites from the 3.48 billion-year-old Dresser Formation, Pilbara, Western Australia. 


What does life look like?

Stromatolites are laminated rock structures formed by the mineralisation of sequentially layered mats of microbes. Modern examples are known from across the world. By imaging the microstructures of such rocks, the team were able to investigate the growth, formation, mineralisation and preservation of samples from Earth’s oldest stromatolite horizons.

They found no microfossils or organic materials, but instead mineralised structures featuring many characteristics consistent with biological life. 

One example of a biological characteristic found in these stromatolites is their domed laminations and surface structure, sometimes compared to an egg box shape. Biology tends to grow towards a nutrient source, and this type of topography is indicative of biological growth, in this case, towards the sun. A second example are features known as palisade structures, which form as a result of microbial growth in modern organisms. The presence of dome topography and palisade structure are two instances of growth witnessed in the Dresser Formation stromatolite samples, and are consistent with photosynthetic organism growth processes. Together with an ensemble of other microstructures, these structures enabled the team to build a convincing case for the biological origin of these ancient and controversial stromatolites. 

Dr Hickman-Lewis says, ‘If an archaeologist discovered the foundations of a ruined city, they would nonetheless know it was built by people because it would bear all the hallmarks of being built by people – doorways and roads and bricks. In very much the same way, there are numerous structural elements integral to stromatolites that allow us to identify their processes of formation and decode their origins. We can almost be archaeologists in deep time.’


Mars 2020

By better understanding the most ancient traces of life on Earth, scientists will be able to use them as comparative materials for potential traces of life on Mars. 

The environment of the Dresser Formation during the formation of the stromatolites almost 3.5 billion years ago was similar to that which is believed to have existed at the edges of Jezero crater on Mars, where the Perseverance rover is currently exploring. Over three billion years ago, the crater would have hosted an enormous lake which could potentially have provided a habitat for Martian life.

Finding evidence of Martian life is one of the principal goals of the Perseverance rover, which is equipped with a range of sophisticated equipment that could be used to find stromatolites on Mars.

Prof Caroline Smith, Head of Earth Science Collections at the Natural History Museum and co-author on the paper says, ‘This paper mimics what we’re doing with the NASA Mars 2020 rover. Using cameras installed on Perseverance, scientists like Keyron can pinpoint potential samples, with features seen in stromatolites here on Earth, before using the rover’s scientific payload to investigate in finer detail. By honing this process here on Earth, we are increasing our chances of finding life on Mars.’ 

The study also provides ideas of the analytical strategies we might apply when Martian samples are brought back to Earth in the 2030s to be worked on by an international team of specialists. Similar multi-technique approaches using high-resolution imaging and chemical instrumentation in Earth-based laboratories will be applied to the samples currently being collected by the Perseverance rover. These techniques will help scientists to answer crucial questions about Mars, including whether life ever existed on the Red Planet. 


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