All the present continents were once together in a single landmass that scientists called Pangaea (Greek for "all earth"). (In fact, this configuration has occurred more than once throughout earth's history.) Pangaea from the Early Triassic is shown below.
As Pangaea split up over the last 200 million years or so, the continents moved into their current positions on the earth's surface. (See the world map below.)
In the process, a mountain chain on Pangaea was split as the Atlantic Ocean opened between Africa and North America. The Atlas Mountains in northwest Africa, the Caledonides in the British Isles, and the Appalachians in the eastern United States were once parts of the same mountain chain!!! At the same time, the plate on which India rides moved north to collide with the Eurasian plate. Prior to the collision that formed the Himalayas, the leading (oceanic) edge of the Indian plate was shoved under the Eurasian plate (a process called subduction).
Eventually, as the oceanic lithosphere was totally subducted, the Indian subcontinent was brought into contact with the Eurasian continent, crumpling the edge of the Eurasian plate and creating the world's highest modern mountains.