Mars Was Habitable Between 3.8 and 3.1 Billion Years Ago: Study

Updated | Mars would have had conditions right for life to survive for around 700,000 years, between 3.8 and 3.1 billion years ago, scientists have discovered.

By analyzing rocks from the Gale crater—a 96 mile wide depression that was once a vast lake—scientists have shown the conditions on Mars over various periods. Their research, published in the journal Science, reveals how the climate changed from a cold one to a warm, temperate one in which life may have thrived.

Study author Joel Hurowitz tells Newsweek the Gale crater is ideal for studying Mars's ancient climate, and that evidence collected by NASA's Curiosity Rover, which is located there, is increasingly showing what conditions would have been like in the past.

"One of the things we're really learning from Gale crater is that Mars—in its ancient geological history — really was home to environments that were very Earth-like in their quality. We're talking about a lake that was being fed by freshwater rivers, it was a standing body of water that was there for a long period of time that had lake chemistry very similar to what we see on Earth.

"This idea that Mars in its early history might have been a more Earth-like place—we're demonstrating one the ground that this really was the case. We can place ourselves onto the surface of another planet and imagine what it would be like at one time in its history—and it would've looked quite similar to what Earth looks like."

In the latest study, the team looked at rocks gathered by Curiosity over the 1,300 days it has been there. Samples were gathered from various depths, providing the researchers with the opportunity to track changes in the chemical and mineral compositions. This allowed them to reconstruct the conditions in the lake when the rocks would have formed.

Findings showed Mars's climate underwent two major transitions. It started off very cold, and then warmed up to temperate conditions. Eventually, around 3.8 billion years ago, it dried up as the planet lost its atmosphere to space.

"We don't understand rock chemistry quite as well as on Earth, so it's difficult to ascribe a specific climate condition," Hurowitz says. "If we were looking at the same rock chemistry on Earth, we would probably be comfortable saying some of the rocks were probably deposited in conditions consistent with a glaciated landscape, while some of the others might be more consistent with a temperate climate. We can say it's colder and warmer, but exactly what the climate condition was is a little more difficult."

While the team could not say exactly when these changes took place, it allowed them to narrow down the time frame during which the Gale crater would have had conditions that could support life. In the study, they narrow this down to between 3.8 and 3.1 billion years ago.

"What the study establishes is that there were places on Mars in its ancient history that had all of the necessary components for life to take hold and survive in those environments," he says. "Mars had all the necessary ingredients to provide an environment where life as we know it would be perfectly happy living in."

Having more evidence to show Mars could have been habitable for a prolonged period in its history helps scientists consider what sort of climate the planet must have had in order for a lake to exist in the Gale crater. "In my mind, that means a more earth-like climate than what we see on the surface of Mars today," Hurowitz says.

As Curiosity continues to make its way up the Gale crater, scientists will get even more opportunity to analyze its rocks and get a better understanding of Mars's geological and climatic history.

"It's' a real opportunity to study the long-term climate history of another planet," Hurowitz says. "It provides us with guideposts for the right types of environments to go looking for biosignatures on the surface of Mars when we land there with future missions. We're learning a lot about the nature of ancient environments on Mars—and where the right places might be to look at in more detail in the search for evidence of life on Mars."

Commenting on the study Andrew Coates, Professor of Physics and Deputy Director (Solar System) at UCL's Mullard Space Science Laboratory, U.K., said: "This is an interesting and exciting set of results from the Curiosity rover, which challenges our understanding of Mars climate history. It's claimed that the results provide good evidence for a transition from cooler, drier to warmer, wetter climate conditions between 3.8-3.1 billion years ago.

"But much of the previous evidence, and results from more global missions, such as Mars Express and Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), indicate the opposite—warm, wet to cooler, drier in the same period."

He says Mars lost its magnetic field between four and 3.8 billion years ago and that this caused the planet to lose its atmosphere and some of its water. "The intriguing evidence here is from analysis of changes over time in mudstones left by an ancient lake in Gale Crater on Mars between 3.8 and 3.1 billion years ago, during which time parts of the lake were shown to be potentially habitable," he says.

"The lake, at much lower altitude than its surroundings, was fed by streams from a wide area. The results are from studying sediment depositions from locations differing by 100 meters in altitude. The climate conditions in Gale crater must have been warm enough to sustain a lake there, and potentially the results are related to a wider area which may help explain the differences. Also parts of the deposition history are indeed consistent with warm, wet to cold, dry global climate.

"Overall the paper shows the power of measurements from a rover in a particular location on Mars, Gale crater, but reminds us that we also need the global context to make sense of the measurements. We look forward to further exciting times in 2020, with the launch of the ExoMars 2020 rover, which will search directly for signs of past life underneath the Martian surface for the first time."

This story has been updated to include comments from Andrew Coates.