Hiding beneath the dusty surface of Mars, NASA’s curiosity rovers have found compelling evidence that the carbon cycle once operated on the Red Planet, which could solve one of the greatest mysteries about Martian’s past atmosphere.
The discovery, published in a scientific release on April 17, 2025, reveals a large amount of sediment from spores (carbonate minerals) in three drill samples collected from Mount Sharp, Gael crater on Mars. This discovery may explain what happened to the carbon dioxide that once made the Martian atmosphere thick enough to support the flow of water.
“The discovery of abundant iron ore at the Great Wind Crater is both a surprising and important breakthrough in our understanding of Martian geology and atmospheric evolution,” said Benjamin Tutolo, assistant professor at the University of Calgary and lead author of the study.
Scientists have long believed that Mars once had a dense atmosphere of carbon dioxide and surface water, which should interact with Earth’s rocks to form carbonate minerals. However, previous roamer missions and satellite observations have not detected the predicted number, leading to what researchers call the “missed carbonate” mystery.
The researchers analyzed powdered rock samples using the rover’s Chemistry and Minerals (Chemin) instrument (Chemin) instrument (Chemin) instrument, and the researchers found that due to curiosity climbing sharp curiosity, the concentrations in three of three samples obtained from different elevations ranged from 4.8% to 10.5%.
“Drilling on a layered Mars surface is like browsing a history book,” explains Thomas Bristow, a research scientist at NASA AMES and co-author of the paper. “A reduction of only a few centimeters gives us a good idea of the minerals formed on or near the ground about 3.5 billion years ago.”
What makes this finding particularly important is evidence of partially closed carbon cycles. In some samples, researchers found that hydroxy iron hydroxyoxide (meter formed when the authorities partially dissolved) showed that some isolated carbon dioxide was later released back into the atmosphere.
In these layers, the presence of gratinite rocks beside magnesium and calcium sulfate suggests that evaporation plays a key role. As ancient wetlands driered, water became increasingly concentrated, triggering mineral precipitation. This mineral pattern tells researchers about changes in the Martian environment, revealing how planets transition from wet to dry conditions.
If similar carbonate deposits exist in other sulfate-rich areas of Mars, they can represent large reservoirs of ancient atmospheric carbon dioxide, which is equivalent to atmospheric pressures of 2.6 to 36 mbar. For comparison, Mars’ current atmosphere contains only about 6 mm of carbon dioxide.
This discovery helps solve how Mars loses its warmer, wetter conditions. Some carbon dioxide escapes into space, and a large amount of carbon dioxide is locked into minerals below the surface. Unlike the Earth’s balanced carbon cycle, Mars’ cycle eventually becomes a direction, more isolated than the carbon released.
This finding also demonstrates why orbital instruments may not have detected these carbonates earlier, they may be masked by other minerals or hidden beneath the surface and require direct sampling to reveal their presence.
As curiosity continues to move forward to Mount Sharp, researchers hope to discover more evidence about Mars’ ancient climate and the process of turning it into the cold, dry world we see today.
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