Although it’s not all that commonly known, an experiment conducted by NASA’s Viking Mars lander in 1976 really did come back positive for signs of life on Mars. The experiment produced not one but four separate positive results, each indicating microbial respiration and standing in stark contrast to the “control” samples captured by a different lander some 4,000 miles away. It seemed at the time that one of mankind’s most longstanding mysteries had been solved: we are not alone in the universe, and apparently, life is common enough to be found on two neighboring rocks in our own solar system.

But then a subsequent test, meant to confirm this mind-blowing revelation by identifying organic matter in the soil, came back negative. NASA quickly concluded that the first test, dubbed LR for “Labeled Release” tests, must have produced four false positives. Not only did they dismiss the four life-affirming tests out of hand, but in the four intervening decades since, they have never attempted to recreate the original tests. In fact, they’ve never even conducted similar testing again. Now, Gilbert V. Levin, who was the principal investigator assigned to the LR tests, has come out to contend that the tests conducted by the Viking lander on July 30, 1976 were proof positive of life on the Red Planet, and he’s got more evidence to back it up.

Surface of Mars, as soon by Viking 2. (NASA)

In a piece Levin penned for Scientific American, he lays out his argument, first pointing out that the test NASA so readily dismissed back in 1976 underwent a rigorous vetting process to ensure that it was both effective as a means to detect life and, more importantly, extremely reliable.

The Viking LR sought to detect and monitor ongoing metabolism, a very simple and fail-proof indicator of living microorganisms. Several thousand runs were made, both before and after Viking, with terrestrial soils and microbial cultures, both in the laboratory and in extreme natural environments. No false positive or false negative result was ever obtained. This strongly supports the reliability of the LR Mars data, even though their interpretation is debated,” Levin wrote.