Scientists at NASA have just made a startling discovery on the surface of Mars that could have a huge impact on the future search for alien life on the Red Planet that experts believe was once covered with water, at least in parts. Scientists have found that an ancient lake on Mars may have provided stable environmental conditions, but those conditions differed significantly from one part of the lake to the other, based on data gathered from NASA’s Curiosity rover.

Differt parts of the lake had conditions that were favorable for different types of microbes, scientists found after diving deep into the data gathered by Curiosity over the first three and a half years of its mission. In the past, scientists have found the existence of a lake that was in Mars’ Gale Crater more than three billions years ago.

The study, titled “Redox stratification of an ancient lake in Gale crater, Mars,” was published in the journal Science. The oxidant stratification observed in these Martian lakes is actually pretty common in lakes on Earth, and the discovery of it on Mars is a strong indicator that Mars was at least capable of hosting life. Whether it actually did is the holy grail scientists are still searching for.

“We’re learning that in parts of the lake and at certain times, the water carried more oxygen,” said Roger Wiens, a planetary scientist at Los Alamos National Laboratory and co-author of the study, published today in the journal Science. “This matters because it affects what minerals are deposited in the sediments, and also because oxygen is important for life. But we have to remember that at the time of Gale Lake, life on our planet had not yet adapted to using oxygen–photosynthesis had not yet been invented. Instead, the oxidation state of certain elements like manganese or iron may have been more important for life, if it ever existed on Mars. These oxidation states would be controlled by the dissolved oxygen content of the water.”