Rotorua research leads to Mars
A New Zealand scientist’s research into hot springs near Rotorua helped identify the oldest site for terrestrial life found on Earth and is helping guide Nasa’s search for ancient life on Mars. It’s Marsden-winning work. Will Harvie reports.
Professor Kathy Campbell is a hot springs expert. The California-trained University of Auckland astrobiologist spent long years researching hot springs, geysers, vents and other places where hot or warm water rises to the surface.
It wasn’t glamorous but it was invaluable because hot springs on land are hot topics these days. Campbell was on the team that earlier this year published a short paper on an ancient hot spring in Western Australia that showed convincing evidence ‘‘indicative of life’’ dating back 3.48 billion years.
The site pushes the oldest terrestrial site for life back by 580 million years. Before these findings, the world’s oldest evidence for life on land was from organic soils in South Africa about 2.8b years old. The oldest evidence of life may be in marine rocks Greenland dating back 3.7b years.
The Marsden Fund – New Zealand’s most prestigious science award – was impressed enough to grant Campbell and colleagues $958,000 to follow up.
Most in the field still think life on Earth originated in oceanic hot springs. Finding convincing evidence of life at a terrestrial spring where hot water was clearly present, but not in huge quantities, shows that ‘‘life got onto land very early’’, Campbell says.
She’s ‘‘not saying’’ life originated there, but makes the case that a hot springs is one candidate among several.
The other reason hot springs are hot is that in 2020 Nasa will launch a rover to Mars with the primary mission of finding evidence of ancient life. The US space agency is deep into talks about where to send the rover and a terrestrial-looking hot spring is on the short list of three sites. Campbell and colleagues are among those making the case.
There are strong similarities between the West Australian site and the Columbia Hills candidate on Mars.
‘‘We’ve got an analogue case with rocks about the same age,’’ she says.
Life could have evolved about the same time on both planets. Alternatively, if it happened on Earth, why didn’t it happen on Mars?
Campbell came to Western Australia and Mars via Rotorua and other geothermal sites in New Zealand. Some of them are very young but they produce a unique rock type called ‘‘geyserite’’ that ‘‘only forms around the vents of hot springs on land’’, Campbell said. Geyserite isn’t found in geothermal sites in deep seas, deltas or shallow water.
She and colleagues found the unique signature of geyserite in the 3.48b-year-old Dresser Formation of the Pilbara Craton, about 1200 kilometres north of Perth.
There was also evidence of shallow ‘‘feeder veins’’ that got hot water to surface, evidence of patchiness and other indicators of terrestrial hot springs.
Among that rock were a ‘‘suite of microbial biosignatures’’, according to the short paper.
These included fossilised stromatolites, the remnants of structures created by microbes. Stromatolites are very widely accepted as evidence of primitive life.
There was also evidence of microbial textures that grew around hot spring pools.
They also found features that look like bubbles that might have been formed by gasses released by bacteria and trapped in an ‘‘elastic medium’’ exuded by microbes and mineralised.
The bubble theory is the most controversial aspect of the short paper, Campbell said, because bubbles can form by inorganic processes.
‘‘The key thing was geyserite associated with stromatolites,’’ she said in an interview.
She paints a picture of archaea, the most primitive living things on Earth, burbling away in small, patchy pools of water with plenty of dissolved minerals and concentrated elements that early life could depend on. It was surprisingly diverse, she said.
Many of these conditions still exist on Earth – in geothermal vents near Rotorua, for example – where microbes release bubbles that are trapped in the gooey stuff before being coated with silica from the hot spring water and forming a durable rock deposit.
Nasa and others in the field believe those conditions once existed on Mars, including at Columbia Hills. However, Nasa’s Spirit rover explored the area between 2004 and 2010 and the appetite to return is weak. According to the letter in February this year identifying the top three sites, the Columbia Hills site ‘‘compares unfavorably’’ with the other two.
At the Jezero Crater site, water flowed at least twice about 3.5b years ago. Scientists think the water carried clay minerals from the surrounding area and the remains of microbial life might be found in lake bed sediments.
At the NE Syrtis site, underground heat sources made hot water flow and surface ice melt. Microbes could have flourished here. Importantly, the layered terrain probably holds a rich record of water and mineral interactions during early Mars history. A decision is expected next year.
Whatever happens on Mars, Campbell and colleagues are currently writing a long version of their paper and will use the Marsden grant to return to Western Australia with a drilling rig. The 14 kilometre-long rock formation she and colleagues studied was weathered and ‘‘not as pristine we’d like’’, she said.
To get more evidence, they want to extract samples from the same layer from underground. They might even find chemical evidence of ancient microbial metabolism in the rock, which would bolster the case for early terrestrial life. A drilling date has not been set.
Meanwhile, Campbell has launched a new research centre at the University of Auckland called Te Ao Ma¯ rama – Centre for Fundamental Inquiry. She is the inaugural director and will ask questions such as: How did life originate from non-living matter? How is life distributed in the universe? Was the Big Bang a unique event? What if the fundamental laws of physics were different elsewhere?