Earth’s Crust: Surprisingly Holds More Water Than Ice Caps, Study Finds

The notion that Earth is predominantly a water-covered planet is familiar to many, with an impressive 71% of its surface enveloped by oceans. However, the question of whether water exists within Earth’s crust and the extent of this water has intrigued scientists.

Recent research published in 2021 in the journal Geophysical Research Letters has shed light on this mystery, revealing that there’s a substantial amount of water beneath Earth’s surface, surpassing the volume found in the planet’s ice caps and glaciers.

According to a discussion with Live Science, Grant Ferguson, a hydrogeologist at the University of Saskatchewan and the study’s lead author, estimated that about 43.9 million cubic kilometers (10.5 million cubic miles) of water are stored within Earth’s crust. This figure starkly contrasts with the volumes of water stored in ice across the globe: about 27 million cubic kilometers (6.5 million cubic miles) in Antarctica, 3 million cubic kilometers (720,000 cubic miles) in Greenland, and 158,000 cubic kilometers (38,000 cubic miles) in glaciers outside of these regions.

Despite these findings, the oceans continue to be Earth’s most significant reservoir of water, containing around 1.3 billion cubic kilometers (312 million cubic miles) of water. This makes groundwater the second largest reservoir of water on the planet.

The 2021 study broadened the scope of previous assessments by including groundwater up to 9.98 kilometers (6.2 miles) deep within Earth’s crust, particularly in sedimentary rocks known for their porosity compared to crystalline rocks. This reevaluation led to the doubling of previous groundwater estimates from roughly 8.5 million cubic kilometers (2 million cubic miles) to 20.3 million cubic kilometers (4.9 million cubic miles), a volume nearly matching the 23.6 million cubic kilometers (5.7 million cubic miles) estimated for shallow groundwater.

The significance of discovering such vast amounts of deep, mostly saline groundwater, which is cut off from the planet’s other water sources, cannot be overstated. According to Ferguson, some of this water has been secluded for incredibly long periods, providing a unique window into Earth’s geological past.

Ferguson points out the largely unexplored nature of these deep waters, considering them a new frontier in scientific research. He suggests that these waters could not only reveal crucial insights into the history of our planet but might also support existing microbial ecosystems. Understanding these ecosystems could offer clues about the evolution of life on Earth, highlighting the profound importance of Earth’s underground water reserves.