• Choose the missing prepositions from the drop-down menus below.
  • Click the button at the bottom to check your answers.
  • Press the "refresh" button on your browser to play again.

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

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

Back to the Earth's axis lesson.

Share this lesson

More Free Sites by Sean Banville

Online Activities