Delving deep: Earth's crust holds more water than its ice caps, reveals study

We've all grown up hearing that Earth is a blue planet, with the majority of its surface — a whopping 71 per cent or three quarters — covered with water.

But, is there any water in Earth's crust? If so, how much water lies underground?

Underground water

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Yes, as per a 2021 study published in the journal Geophysical Research Letters, there is more water underground or under the earth's surface than in the planet's ice caps and glaciers.

This underground water is held in soil or in pores in rocks, and the amount there is may shock you.

Talking to Live Science, Grant Ferguson, a hydrogeologist at the University of Saskatchewan and lead author of the 2021 study, revealed that the Earth's crust holds approximately 43.9 million cubic kilometres (10.5 million cubic miles) of water.

In comparison, Antarctica's ice contains about 6.5 million cubic miles (27 million cubic km) of water, Greenland's ice holds around 720,000 cubic miles (3 million cubic km). Additionally, glaciers outside Antarctica and Greenland have about 38,000 cubic miles (158,000 cubic km) of water.

Nevertheless, the oceans on Earth's surface remain the planet's largest water reservoir, holding approximately 312 million cubic miles (1.3 billion cubic km) of water.

Now we know that after oceans, groundwater is the Earth's largest water reservoir.

The 2021 study has expanded previous estimates by considering groundwater within the upper 6.2 miles (9.98 kilometres) of Earth's crust, including sedimentary rocks, which are more porous than crystalline rocks. With this, our previous estimates of groundwater have more than doubled from about 2 million cubic miles (8.5 million cubic km) to 4.9 million cubic miles (20.3 million cubic km).

This new estimate, as per Live Science, is nearly as large as the 5.7 million cubic miles (23.6 million cubic km) calculated for shallow groundwater.

Why does this matters?

The deeper groundwater, which is mostly salty, is isolated from the rest of the planet's water and as per the scientists, has been trapped for extraordinarily long spans of time in some places. This, as per Ferguson, can offer valuable insights into Earth's history.

"We know very little about these waters at depths greater than a few kilometres, making it a frontier area for science," he said. Furthermore, he said that the water may support microbial ecosystems that are still active today, which can help ascertain how life evolved on Earth.

(With inputs from agencies)