The surface of the earth is above tectonic plates which got separated millions of years ago due to the thermal currents in the Aesthenosphere. Some plates are moving away from each other which are called Divergent Plates. Whereas some plates are moving towards each other which are called Convergent Plates. The five Tectonic Plates are:
North American Plate
South American Plate
Eurasian Plate
Indo-Australian Plate
Antarctica Plate

It cannot be said that when they will collide. But it has happened in the past due to which the Himalayan Ranges got formed. 
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