NASA's Mars 2020
Scientists from NASA's Mars 2020 and ESA's ExoMars projects study stromatolites, the oldest confirmed fossilized lifeforms on Earth, in the Pilbara region of North West Australia. The image was taken on Aug. 19, 2019 NASA/JPL-Caltech

As any geologist worth his or her salt will tell you, there are rocks, and then there are rocks. Next July, NASA and the European Space Agency (ESA) are launching rovers to Mars that will search for signs of past microbial life, and to find them, the scientists with NASA's Mars 2020 mission and ESA's ExoMars will need to examine different kinds of rocks that lend compelling insights into the environment in which they were made - all from 100 million miles away.

"While we expect to find many significant rocksduring both Mars 2020 and ExoMars missions, we also have to leave open the possibility we could find one or more very specialrocks,the kind whose discovery would not only speak volumes about the history of Mars but contribute significantly to the discussion of life elsewhere in the universe," said Ken Farley, Mars 2020 project scientist at Caltech in Pasadena.

Could Mars ever have supported life? In the Australian Outback, scientists from NASA's upcoming Mars 2020 mission and their counterparts from the joint European-Russian ExoMars mission visited the oldest convincing evidence for life on Earth to prepare for their own searches for signs of ancient life on Mars. The field lesson in astrobiology in the Pilbara region is being applied in the near term by NASA, ESA and Roscosmos for mission planning, and will also pay dividends when both rovers begin to send back science data and imagery from the Red Planet.

Guided by Martin Van Kranendonk, director of the Australian Centre for Astrobiology at the University of New South Wales, members of the two missions' science teams went on an expedition to northwestern Australia's Pilbara region to analyze, discuss and debate stromatolites - structures preserved in rock that formed in water on early Earth and contain a fossilized record of ancient microbial life. Among the science teams' stops: a stromatolite cluster in a grouping of rock called the Dresser Formation that contains some of the oldest known fossilized records of life on our world.

"Some 3.48 billion years ago, this area was home to a caldera, or collapsed volcano, filled with hot, bubbling seawater," said Van Kranendonk. "At the same time, this location was also home to structures called microbial mats - visible to the naked eye but composed of microscopic organisms. Today you would know them as simple pond scum, but back then they were the most complex lifeforms on Earth."

Likely powered by photosynthesis, along with the heat and chemical energy in the caldera, these mats lived at the water's edge, secreting a mucous that would trap grains of sediment swirling around in the water. Over time, sheet after sheet of these microbes trapped sediment on top of previous layers. When the seawater receded and the pond scum dried up and disappeared millennia later, what remained was striking evidence of this co-evolution of geology and biology.

"A stromatolite is quite subtle to the untrained eye," said Van Kranendonk. "But once you know the details, you recognize that these wavy, wrinkly rocks have a structure different from that which can be explained by just geology."

The launch window for Mars 2020 opens on July 17, 2020. It will land at Mars' Jezero Crater on Feb. 18, 2021. The launch window for ExoMars opens July 25, 2020. It will land at Oxia Planum in March 2021. JPL is building and will manage operations of the Mars 2020 rover for the NASA Science Mission Directorate at the agency's headquarters in Washington. The ExoMars program is a joint endeavor between the European Space Agency and the Russian Federal Space agency Roscosmos.