Djokic said it is possible her discovery will swing the debate in favor of Columbia Hills, since “If life can be preserved in hot springs so far back in Earth’s history, then there is a good chance it could be preserved in Martian hot springs too.” On the other hand, if hot springs really were the starting point for life on Earth, it is bad news for proposed missions to study moons in the outer Solar System where a layer of ice conceals an ocean with likely hydrothermal vents beneath.
Djokic was able to determine the springs she was studying were above ground, rather than being in shallow parts of the ocean, because they contain geyserite, a mineral deposit restricted to freshwater environments. Geyserite is formed when high-temperature silica-rich fluids are exposed to water. Prior to her work, no geyserite had been identified that was more than 400 million years old. Djokic told IFLScience it was not clear why such a large gap in the fossil record should exist, but she pointed out that volcanic environments are, by their nature, highly changeable, and many older sites may have been destroyed in eruptions.
Discovering such old geyserite would be interesting on its own. However, the reason Djokic's work was published in Nature Communications is that within the same ancient springs she found stromatolites, the layered communities of microbes that, in fossil form, represent some of our oldest evidence of life. Other indications of microbes, such as well-preserved bubbles, were also trapped in the same rocks. “This shows a diverse variety of life existed in fresh water, on land, very early in Earth’s history,” said co-author Professor Martin Van Kranendonk.
Some of what Djokic found looks a lot like fossils we have seen before in other environments, but she told IFLScience the bubbles and textures seen in some of the rocks look more like those seen around modern hot springs than at other ancient sites. Although we know little about the microbes that left these signatures behind, Djokic said there was probably a mix of life-forms living off sunlight and the chemical energy the springs provide.
These rocks in the Dresser Formation, Western Australia, include layers of geyserite, demonstrating the presence of long gone hot springs 3.48 billion years old.