Here on Earth, 95 percent of all methane molecules are the product of living chemistry.
Now, scientists have found signs of complex, macromolecular organic matter in samples of the crater's 3-billion-year-old mudstones - layers of mud and clay that are typically deposited on the floors of ancient lakes.
The discoveries were found using the US space agency's Curiosity Mars Rover, which has been studying the Red Planet's surface since it first landed in 2012.
Dr Eigenbrode hopes further details about the nature of the carbon molecules will emerge with future missions, such as the European Space Agencies ExoMars Mission or NASA's Mars 2020 mission. The Viking Project was the first USA mission to safely land spacecraft on the Martian surface, as well as send back images.
Decades later, Viking helped inspire the instruments on today's Martian rovers.
Curiosity tested out the technique using it to drill a 2-inch-deep hole into a target called Duluth.
Since Curiosity landed on Mars in 2012, the rover has been exploring Gale Crater, a massive impact crater roughly the size of CT and Rhode Island, for geological and chemical evidence of the chemical elements and other conditions necessary to sustain life. The two rock samples, from sites named Confidence Hills and Mojave, are at the bottom of Gale Crater. It likely held a lake, and now includes a mountain.
Methane's presence on Mars is puzzling, because it survives only a few hundred years at a time, which means that somehow, something on the red planet keeps replenishing it. And, she says, it gives us an idea where to look. That's because the surface of Mars is constantly bombarded with radiation that can break down organic compounds.
"This is a significant breakthrough because it means there are organic materials preserved in some of the harshest environments on Mars", said lead author of one of two studies in Science, Jennifer Eigenbrode, an astrobiologist at NASA Goddard Spaceflight Center. Gale Crater's rim is visible on the horizon. In 2009, researchers reported that inexplicable martian plumes randomly belch out thousands of tons of methane at a time. With five years of data from a single location, they now have answers. The timing of the pulses provides an important clue.
Webster and his colleagues suspect that the methane comes from deep underground, and temperature swings on Mars's surface throttle its flow upward. And, of course, there is always the chance that Martian methanogens still slumber in the planet's subsurface even today, periodically awakening during clement periods to produce their gaseous calling-card.
Detecting this organic molecule in the atmosphere, combined with the finding of organic compounds in the soil, has strong implications about potential life on Mars in its past. In chemistry, almost all molecules containing both carbon and hydrogen are organic compounds. Then, the conditions would have been comparable to Earth.
NASA's InSight Lander, launched on May 5, will land on Mars on November 26.
This work was funded by NASA's Mars Exploration Program for the agency's Science Mission Directorate (SMD) in Washington. I want to know their story. What the study has done, though, is to propel the search for life on Mars higher up the list of global space exploration priorities - giving space agencies ammunition to argue for a coordinated programme of missions to explore the Red Planet. "The first one would be life, which we don't know about".