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Perhaps it's only geophysicists who are [aware / beware] of the importance of underground reservoirs [on / of] maintaining Earth's balance. Geophysicist Ki-Weon Seo from Seoul National University [has / had] discovered that humans have extracted so much groundwater from under our feet that they have [changed / charged] the tilt of Earth's axis. This [shaft / shift] has been significant enough to physically relocate [a / the] geographic North Pole. The mass of polar ice is [drifting / drafting] by 4.36 centimetres a year. Professor Seo calculated that we [exacted / extracted] more than two trillion tons of groundwater between 1993 and 2010, causing Earth to [cobble / wobble] . Seo added that the pumping of groundwater has caused sea levels to [raise / rise] by 6.24 millimetres.

Professor Seo explained how groundwater [affects / effects] Earth's gravity. He said: "Every [moss / mass] moving around on the surface of the Earth can change the rotation [axle / axis] ." Scientists have only recently discovered how groundwater can change Earth's axis. They previously [belief / believed] water-driven shifts were caused by melting glaciers and ice [cups / caps] . Seo and his colleagues were puzzled at [what / how] this could cause such a tilt. They concluded that the [depletion / repletion] of underground water was also a factor. Much of the extraction of groundwater is [due / up] to irrigation, especially [in / at] north-western India and western North America. Another researcher said: "The very way the planet wobbles is impacted [on / by] our activities."

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