Scientists have uncovered new evidence to suggest that Earth is leaking gases from deep inside its mantle - even in regions without any volcanic activity.
Led by researchers at The University of Manchester, the study reveals that invisible, odourless gases like helium and argon are slowly seeping hundreds of kilometres up through Earth's crust, reaching underground water supplies thousands of meters beneath our feet.
For decades, scientists have believed that the vast majority of Earth's internal gases are either pushed deep underground through tectonic activity, or escape back to the surface through volcanic eruptions.
The new research, published in the journal Nature Geoscience, challenges this understanding and the findings could give scientists a better idea of the geological and chemical processes that take place deep inside the Earth.
"Think of it like a having small puncture in your car tyre," said lead author Dr Rebecca Tyne, Dame Kathleen Ollerenshaw Fellow at The University of Manchester.
"We've discovered a steady trickle of gases coming from deep within Earth, even though there's no obvious volcanic activity on the surface.
"This passive degassing of the mantle may be an important, yet previously unrecognised process and these findings will help our understanding of how our planet's interior works and how much gas is escaping into the atmosphere over time. It could even play an important role in the geologic carbon cycle"
The researchers analysed groundwater from 17 wells in the Palouse Basin Aquifer in the United States - a key source of drinking water in a region considered to be geologically stable.
Using advanced measurement techniques, they measured for multiple types of helium and argon and found signatures to suggest these gases had travelled up from the Earth's mantle - the hot, dense layer between the outer crust and the core. Importantly, the helium and argon gases detected are inert, meaning they do not react chemically or affect water quality.
Co-author Dr Mike Broadley , NERC Independent Research Fellow at The University of Manchester, said: "We found evidence of mantle-derived gasses in 13 out of the 17 wells. These gases - especially helium-3 and argon-40 - do not form in the atmosphere or in shallow rocks, they come from a layer of the mantle called the sub-continental lithospheric mantle, many kilometres deep in the Earth."
The highest amount of gas was found in the oldest and deepest groundwater samples - some over 20,000 years old - indicating the gases have been moving slowly but steadily over a long period of time.
The researchers also found a strong correlation between the samples, suggesting they are travelling up together from the same deep source.
Their findings suggest that this kind of low-level, non-volcanic degassing may be more common - and more important - than previously thought. The team are now planning to investigate whether this is a globally consistent phenomenon by investigating groundwaters worldwide.
The research was carried out in collaboration with Woods Hole Oceanographic Institution (USA), Université de Lorraine (France), University of Ottawa (Canada) and the University of Idaho (USA).
Journal: Nature Geoscience
Full title: Passive degassing of lithospheric volatiles recorded in shallow young groundwater
DOI: 10.1038/s41561-025-01702-7
Link: https://www.nature.com/articles/s41561-025-01702-7 [nature.com]
