Martian Meteorites Compared for Evidence of Life


In 1911, approximately 40 stones fell from the sky over Nahkla, Egypt. The rain of rocks was accompanied by detonations and clouds, making the event a memorable one. Stones from the fall ended up in museums across Europe as well as in the Smithsonian Institute. In 1998 a stone from the British Museum was studied by the Johnson Space Center in California and proved to be Martian in origin. The Nahkla meteorite was all the rage. It was the best evidence thus far that Mars may have once boasted a water-and-carbon environment suitable for sustaining life. The Nahkla meteorite can now be compared to another Martian space rock, the Yamoto meteorite, which carries within it even greater evidence for life on Mars.

The Yamoto meteorite has so far won out in comparisons. Where the Nahkla stone can be proven by the atmospheric gases trapped in its matrix to have come from Mars, and shows signs of having been in a watery environment, the Yamoto meteorite has shown evidence not just of having come from the same planet as Nahkla, but of carrying inside it microscopic tracks similar to bacterial activity seen in Earth stones. These tracks, on Earth at least, indicate the presence of biotic life forms that existed in lava flows.

Found embedded in the Yamoto Glacier in Antarctica in 2000 by a Japanese research expedition, the Yamoto meteorite is comprised of Martian clay and is riddled with undulating, curving micro-tunnels similar to the ones made by biotic organisms in basalt on Earth. Such bacteria can survive in lava flows and create tunnels in the cooling stone as they move throughout the flows.

The meteorite also features tiny sphere-shaped inclusions of carbon-rich material sandwiched between layers in the rock. This same feature was found in the Nahkla stone and in other Martian meteorites, and is the reason this family of meteorites has been classified as “nahklites.”

This carbon could come from other sources than biotic activity, though the presence of carbon usually signals the remains of a life-form in Earth’s geologic material. But in comparing the two meteorites for evidence of Martian life, the Yamoto stone has more features that point to bacterial forms on Mars in the distant past.

There are other meteorites that has been ascertained to have come from Mars and which have shown evidence of biotic life. The Allan Hills meteorite, studied in 1996, has similar features to the Yamoto stone, but Yamoto is much larger and has more structures to study. As well, where the Nahkla and Allan Hills stones were exposed to more possible contamination, the Yamoto stone spent no time in a museum or changing a lot of hands, and is thus a good candidate for pristine readings from the ancient Martian environment.

The Yamoto meteorite fell to Earth approximately 50,000 years ago and was preserved in Antarctic ice, while the fall of the Nahkla stone that gave this class of meteorite its name is part of the historical record. Comparisons between these stones confirm their Martian origin, however. Nahkla and the Allan Hills meteorite showed the presence of structures that might indicate a water environment some time in the distant past of Mars. But in comparing these meteorites, the Yamoto entry shows more evidence of Martian life, and brings us much closer to understanding what that life might have looked like in the landscape of ancient Mars.

By Kat Turner


Jet Propulsion Laboratory

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