Humans Are Changing Earth Kilometers Deep Below Us, Not Just At The Surface

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The causes and possible solutions of the climate crisis are linked to the subsurface.

Oil extraction has changed the interior of the Earth's crust

Image Credit: EpicStockMedia/Shutterstock.com

The changes that our species is making to the planet are deeper than initially thought. Not only are the impacts of human activity changing the surface and climate of the Earth, but new research suggests that we have also changed the deep subsurface, a zone located hundreds of meters to several kilometers beneath where we stand.

A team of researchers looked at the extraction of fossil fuels, such as oil and gas, and their replacement underground using salt water. That is done to maintain the pressure in the reservoir. There's often water already present in these reservoirs - water that has been untouched for millions of years. Adding new water changes the composition as well as how it moves in the subsurface.

There is also hydraulic fracturing, also known as fracking. This is a technique to extract oil and gas, not from reservoirs, but from deep rock formations. Breaking the rocks has led to quakes in regions that are not seismically active, but also introduces water and bacteria to different underground environments.

In general, the data shows that the motion of fluids in the subsurface is much higher under human activity than compared to natural circulation. While this fact is significant, it is currently unclear what the consequences of these changes might be.

"We looked at how the rates of fluid production with oil and gas compare to natural background circulation of water and showed how humans have made a big impact on the circulation of fluids in the subsurface," senior study author Professor Jennifer McIntosh from the University of Arizona said in a statement.

"The deep subsurface is out of sight and out of mind for most people, and we thought it was important to provide some context to these proposed activities, especially when it comes to our environmental impacts," added lead study author Professor Grant Ferguson.

The many unknowns about the subsurface lead to concern when it comes to possible solutions to the climate crisis. Some carbon storage solutions aim to bury carbon dioxide from the atmosphere deep underground. 

The extraction of lithium for batteries is also dependent on extraction methods that require a lot of water to be injected into the subsurface. Then the use of geothermal energy as a carbon-free source of electricity might also affect the subsurface. It is important to understand what is going on under us.

"We need to use the deep subsurface as part of the solution for the climate crisis," McIntosh said. "Yet, we know more about the surface of Mars than we do about water, rocks and life deep beneath our feet."

A paper describing the work and the current uncertainties is published in the journal Earth's Future.