How do humans impact Earth’s deep subsurface?

The current fluid movement rates induced by human activities are higher.


Earth’s deep subsurface is a zone that lies hundreds of meters to several kilometers beneath the planet’s surface. Until now, the impact of human activities has been analyzed on Earth’s surface. For the first time, scientists from the University of Arizona investigated the effect on Earth’s deep subsurface.

Scientists compared the fluid production rates from oil and gas to the background natural circulation of water. They demonstrated how human activity has a significant influence on subterranean fluid circulation.

According to the study, measures suggested as responses to climate change are expected to raise these human-induced fluid fluxes. These tactics include lithium extraction from underground mineral-rich brine for use in electric vehicle power plants; geothermal energy production, which involves pumping water through hot rocks to produce electricity; and geologic carbon sequestration, which is the process of absorbing and storing atmospheric carbon dioxide in porous rocks below the surface.

Peter Reiners, a professor at the UArizona Department of Geosciences and a co-author of the study, said, “Responsible management of the subsurface is central to any hope for a green transition, sustainable future, and keeping warming below a few degrees.”

McIntosh says saline water always comes from the deep subsurface when oil and natural gas are produced. The underground water is frequently millions of years old, and it gets its salt from either ancient seawater evaporating or chemical reactions with rocks and minerals.

To maintain reservoir pressure and compensate for the oil withdrawn, additional water from near-surface sources is added to the saltwater for more effective oil recovery. The subsoil is then reinjected with the combined saline water. This starts a cycle where fluid is created and then injected again deep below the surface.

Reintroducing residual saline water from underground is a common procedure in the extraction of lithium, geothermal energy production, and geologic carbon sequestration.

McIntosh said, “We show that the fluid injection rates or recharge rates from those oil and gas activities are greater than what naturally occurs.”

The team discovered that the current fluid movement rates caused by human activity are higher than how fluids moved before human intervention using data from various sources, including measurements of fluid movements related to oil and gas extraction and water injections for geothermal energy. 

Scientists also predicted how human operations like lithium extraction, carbon capture, and sequestration would be documented in the geological record—a record of Earth’s past preserved in the rocks that comprise its crust.

Scientists suggest that human activities could potentially alter the deep subsurface fluids and the microbes living there. Fluid movement may modify microbial environments by changing water chemistry or by bringing new microbial communities from the Earth’s surface to the underground.

For instance, a deep rock formation that has previously shown no discernible microbial activity may suddenly bloom when hydraulic fracturing is used, a method used to fracture subterranean rocks with pressured liquids to recover oil and gas.

Further study is required to find many unanswered questions about Earth’s deep subsurface and how it is impacted by human activities, and it’s essential to continue working on those questions.

Journal Reference:

  1. Grant Ferguson, Lydia R. Bailey, Ji-Hyun Kim et al. Acceleration of Deep Subsurface Fluid Fluxes in the Anthropocene. Earth’s Future. DOI: 10.1029/2024EF004496


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