Is it possible that mankind actually already found life on Mars 40 years ago with the Viking landers? That’s the intriguing possibility that some scientists are raising as the search for life on the Red Planet intensifies.

Two Viking landers became the first U.S. spacecraft from Earth to actually touch Mars back in 1976, and they took some of the very first high-resolution images of the Red Planet, in addition to conducting some experiments to find signs of microbial life.

The experiments resulted in some contradictory results, including one experiment that showed that Martian soil tested positive for metabolism, while another experiment found no evidence of any organic material.

But now, a couple of scientists have published a piece in the journal Astrobiology that claims that they’ve resolved the contradictions and the data seems to suggest that there was life on Mars at one time.

“The 1976 Viking Labeled Release (LR) experiment was positive for extant microbial life on the surface of Mars. Experiments on both Viking landers, 4000 miles apart, yielded similar, repeatable, positive responses,” the paper’s abstract states. “While the authors eventually concluded that the experiment detected martian life, this was and remains a highly controversial conclusion. Many believe that the martian environment is inimical to life and the LR responses were nonbiological, attributed to an as-yet-unidentified oxidant (or oxidants) in the martian soil.

“Unfortunately, no further metabolic experiments have been conducted on Mars,” it continues. “Instead, follow-on missions have sought to define the martian environment, mostly searching for signs of water. These missions have collected considerable data regarding Mars as a habitat, both past and present. The purpose of this article is to consider recent findings about martian water, methane, and organics that impact the case for extant life on Mars. Further, the biological explanation of the LR and recent nonbiological hypotheses are evaluated.”