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Promising the Earth: do these Greenland rocks, billions of years old, contain organic material? Credit: C. M. FEDO/GEORGE WASHINGTON UNIV.

A famous study that found hints of the earliest life on Earth in Greenland rock has been thrown into doubt after researchers failed to replicate the work.

The quartzite rock, which comes from Akilia Island, was reported to contain organic carbon in crystals of a bone-like material called apatite — a promising sign of life (S. J. Mojzsis et al. Nature 384, 55–59; 1996). The rock was dated at about 3.85 billion years old, millions of years older than other signs of life found in Greenland and hundreds of millions of years older than evidence of life elsewhere.

The findings have been disputed before. Some researchers say the carbon cannot be proven to have a biological origin (C. M. Fedo and M. J. Whitehouse Science 296, 1448–1452; 2002). Others have suggested that the rock is not as old as originally thought (Y. Sano et al. Nature 400, 127; 199910.1038/22032).

There is now a fresh challenge. On 11 June at a Goldschmidt Geochemistry conference in Copenhagen, Denmark, Aivo Lepland told scientists that he could not replicate the original study. Lepland, now with the Geological Survey of Norway, Trondheim, and his colleagues spent five years examining 15 different rock samples from the same outcrop in Akilia, but found no organic carbon in apatite crystals.

“I think there must have been a mix-up of samples,” says Gustaf Arrhenius, a geochemist at the Scripps Institution of Oceanography in La Jolla, California, who is the senior author on both the original report and the recent presentation. Arrhenius says a sample from Greenland's nearby Isua formation, where there are organic carbon crystals in younger rock, may have inadvertently been attributed to Akilia. The original study may also have hit upon a genuine but rare find.

The original Akilia rock analysis was performed by Steven Mojzsis, then Arrhenius's doctoral student and now a geochemist at the University of Colorado in Boulder. Mojzsis, who attended the conference, told Nature he doubted there was a mix-up of samples, but he declined to discuss the specifics of Lepland's work. He and Lepland have agreed to divide the original samples for more analysis and have gone to examine Akilia and other sites in Greenland this week.