Scientists have uncovered a previously unknown carbon cycle taking place in the mineral-rich soils of the Mojave Desert, which may play a major role in the Earth's annual carbon exchange. A study published in Science Advances describes a daily cycle in which carbon dioxide (CO2) is absorbed and released by the soil. At night, as temperatures drop, CO2 molecules from the atmosphere attach themselves to minerals and particles in the soil through a process called adsorption. As the sun rises and temperatures increase, these molecules detach and return to the air in gaseous form. Traditionally, scientists have understood soil carbon exchange through biological processes, such as soil respiration. This involves plants absorbing CO2 through photosynthesis, converting it into organic carbon, and then releasing some of that carbon back into the soil through their roots. Microorganisms in the soil then break down this organic material, releasing CO2 back into the atmosphere. However, this new research highlights an alternative mechanism: a non-living, or abiotic, process driven by temperature changes rather than biological activity. Ronald Amundson, a professor and senior author of the study, explained that this process was previously thought to be entirely biological. He likened it to the breathing of a "giant, living organism." However, in hot, dry regions like the Mojave, where vegetation is sparse, this biological activity is limited. Amundson and his team monitored the Mojave using soil sensors since 2017 and found an unexpected pattern: instead of CO2 being released from the soil into the air, it was being absorbed into the soil at night. This was confirmed by measuring CO2 levels at different depths, which showed a flow of carbon dioxide into the soil. Lab tests confirmed that this process is driven by mineral adsorption. Researchers collected soil samples from the Mojave and tested them at Lawrence Berkeley National Laboratory. Using specialized equipment, they measured how much CO2 was absorbed at different temperatures and concentrations. The results showed that as temperatures dropped, the soil's ability to absorb CO2 increased. This confirmed that the observed carbon uptake at night was due to adsorption, not biological activity. If this process occurs in other deserts globally, it could account for 1 to 3 gigatons of carbon—roughly one-tenth to one-third of annual human emissions—moving in and out of desert soils each year. The study notes that this estimate is based only on Mojave soils, and the actual number may be higher. Similar processes have been observed in cold deserts like Antarctica, and scientists have long suspected a similar mechanism on Mars. The discovery also highlights that natural minerals have properties similar to those of synthetic materials designed to capture CO2, such as those developed by Nobel Prize-winning chemist Omar Yaghi. Amundson emphasized that this abiotic process becomes noticeable when biological activity is low. In such conditions, the non-living carbon cycle can be as significant as, or even larger than, the biological one. This finding could lead to more accurate climate models and inspire new, nature-based strategies for carbon management.