Earth's Hidden Water Reserves: How Much Is on the Planet's Crust?

Earth is predominantly a water-covered planet, with approximately 71% of its surface covered by water, mainly in oceans. Apart from oceans, water exists in various forms and locations, including in the atmosphere as water vapor, in rivers and lakes, in icecaps and glaciers, in soil moisture, aquifers, and even within living organisms.

The continuous movement of water, facilitated by the water cycle, ensures its redistribution across the planet, sustaining life as we know it. But how much water is in Earth's crust?

Insights from Groundwater Studies

In a study published in 2021 in the Geophysical Research Letters, researchers discovered that Earth's groundwater reservoirs, nestled beneath the soil or within rock pores, surpass the volume of water contained in its ice caps and glaciers.

Grant Ferguson, a hydrogeologist at the University of Saskatchewan and the primary author of the 2021 study explained that Earth's crust harbors an estimated 43.9 million cubic kilometers (equivalent to 10.5 million cubic miles) of water.

In contrast, Antarctica harbors about 6.5 million cubic miles of water in its ice, with Greenland's ice containing around 720,000 cubic miles. Additionally, glaciers outside these areas add 38,000 cubic miles to Earth's water reserves, as revealed in the study.

Furthermore, groundwater emerges as Earth's primary water reserve, surpassing even the vast oceans, estimated at about 312 million cubic miles. Unlike previous assessments, the 2021 study expanded its scope to include sedimentary rocks, boosting the groundwater estimate from 2 million to 4.9 million cubic miles.

On the other hand, the 2015 Nature Geoscience study concentrated solely on shallow groundwater, approximating its volume at 5.4 million cubic miles.

The 2021 study expanded groundwater estimates to 4.9 million cubic miles by including sedimentary rocks. Shallow groundwater is essential for drinking and irrigation, while deep groundwater offers insights into Earth's history.

Despite the limited understanding of deep groundwater, it represents an unexplored frontier in scientific inquiry, offering significant potential to uncover Earth's ancient geological secrets.

Jennifer McIntosh, a co-author of the study, emphasizes the importance of further exploration of deep-water reserves on Earth and other celestial bodies to deepen our understanding of planetary hydrology and geological processes.

READ ALSO: Large Amounts of Water Detected in the Mantle Might Be a Subterranean Sea Inside the Earth

Crucial Role of Groundwater in Sustaining Life

Over 96% of the Earth's water is saline, found in oceans, while freshwater resources sustain life through rainfall replenishing streams, rivers, lakes, and groundwater. Although surface water is conspicuous, the unseen groundwater plays a crucial role in maintaining water availability during dry spells and sustaining river flow even on rainless days.

While surface water is readily noticeable, the significant volume of freshwater stored underground replenishes rivers through seepage, contributing to vital ecosystems. Groundwater, despite being less visible, is indispensable, providing essential resources for drinking water and irrigation, particularly in arid regions like desert towns in the western United States.

Without groundwater, communities would face severe water scarcity, highlighting its pivotal role in supporting human activities and preventing scenarios like barren landscapes in Palm Springs, California.

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