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Global Positioning System Global Positioning System (GPS) uses recieving stations that are on the Earth to monitor a location.  Observations have shown that the readings of the locations of these stations have moved overtime which says the surface of the Earth is moving.

Sea Floor Sprading

As new ocean crust forms, it obtains the polarity of the Earth's magnetic field at that time.  Over time, the strength of the Earth's magnetic field changes.  The new crust gets a new kind of polarity.  This new crust forms magnetic stripes on the sea-floor.

Ages of Rocks

Scientists have found that volcanic rock from the ocean floor shows that the age of rocks increase from the crest of the ridge.  The ridge is formed by the rising magma in the Sea-Floor Spreading theory.  Scientists have calculated that the Arctic Ridge moves 2.5cm/year and the East Pacific Ridge moves 15cm/year.

The Mid-Ocean Ridge Surveys of the depth of the ocean floor showed a giant mountain range that encircles all the Earth.  It goes between the continents.  The ends of the mid-ocean ridge slope down to the deeper part of the ocean, toward the continents. The ridge is highlighted in blue in the picture.