Well-Preserved Hydrothermal Deposits on Mars Offer a Window Into Early Earth

The Eridania basin of southern Mars is believed to have held a sea about 3.7 billion years ago, with seafloor deposits likely resulting from underwater hydrothermal activity. This graphic shows estimated depths of water in that ancient sea.

Did Mars ever have life? Planetary scientists keep finding intriguing clues of potentially habitable environments in the Red Planet’s distant past. Now, the latest finding shows the best evidence yet of past conditions on Mars that mirror those on Earth billions of years ago, both when and where life began on our planet.

Data from the Compact Reconnaissance Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter show well-preserved seafloor hydrothermal deposits in a large basin in the southern hemisphere of Mars called Eridania.

“Conditions in Eridania are contemporaneous with the earliest evidence for life on Earth in potentially similar environments 3.8 billion years ago, and might provide an invaluable window into the environmental conditions of early Earth,” a team of scientists from institutions in China, the United Kingdom, and the United States wrote in the journal Nature Communications.

Even if life on Mars is never discovered, the site could reveal clues about the conditions on Earth that yielded life, Paul Niles of NASA's Johnson Space Center, Houston, said in a statement. "Volcanic activity combined with standing water provided conditions that were likely similar to conditions that existed on Earth at about the same time — when early life was evolving here," he said.

This view of a portion of the Eridania region of southern Mars shows fractured, dismembered blocks of deep-basin deposits that have been surrounded and partially buried by younger volcanic deposits.

Niles and his fellow researchers say that the basin now contains huge mineral deposits that were formed in a large sea of hot water, heated by volcanic activity. The volcanoes are no longer active and the sea has long since disappeared. These deposits represent the Red Planet's most ancient exposed crust.

They estimate the ancient Eridania Sea held about 50,000 cubic miles (210,000 cubic kilometers) of water, nearly 10 times more than the combined volume of the Great Lakes. The Eridania Sea would have been the largest body of water on Mars, containing as much as all other lakes and seas on Mars combined. Hot springs similar to hydrothermal vents called black smokers on Earth would have pumped mineral-laden water directly into the ancient Martian sea.

The minerals identified from CRISM’s orbital spectrometer include serpentine, talc, and carbonate, which are all evidence of water. Additionally, the shape and texture of the thick bedrock layers are consistent with seafloor hydrothermal deposits.

Additionally, salts were observed only at higher elevations, likely representing a coastal shoreline where, so they feel there are several lines of evidence that strongly suggest Eridania was a sustained inland sea in the late-Noachian period.

"This site gives us a compelling story for a deep, long-lived sea and a deep-sea hydrothermal environment," Niles said. "It is evocative of the deep-sea hydrothermal environments on Earth, similar to environments where life might be found on other worlds — life that doesn't need a nice atmosphere or temperate surface, but just rocks, heat and water."

This diagram illustrates an interpretation for the origin of some deposits in the Eridania basin of southern Mars as resulting from seafloor hydrothermal activity more than 3 billion years ago.

The researchers argue the ancient, deep-water hydrothermal deposits in Eridania basin represent a new category of astrobiological target on Mars because they suggest it was rich in chemical nutrients and energy sources.

“Such a deep-water environment would have been protected from harsh surface conditions and ideally suited for preservation of organic matter under reducing conditions,” they wrote. “In fact, the earliest evidence of life on Earth seemingly corresponds to seafloor deposits of similar origin and age … Eridania seafloor deposits are not only of interest for Mars exploration, they represent a window into early Earth.”

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