<P> During the Upper Cretaceous , about 70 million years ago , the north - moving Indo - Australian Plate ( which has subsequently broken into the Indian Plate and the Australian Plate ) was moving at about 15 cm per year . About 50 million years ago this fast moving Indo - Australian Plate had completely closed the Tethys Ocean , the existence of which has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges . Since both plates were composed of low density continental crust , they were thrust faulted and folded into mountain ranges rather than subducting into the mantle along an oceanic trench . An often - cited fact used to illustrate this process is that the summit of Mount Everest is made of marine limestone from this ancient ocean . </P>
<P> During the Upper Cretaceous , about 70 million years ago , the north - moving Indo - Australian Plate ( which has subsequently broken into the Indian Plate and the Australian Plate ) was moving at about 15 cm per year . About 50 million years ago this fast moving Indo - Australian Plate had completely closed the Tethys Ocean , the existence of which has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges . Since both plates were composed of low density continental crust , they were thrust faulted and folded into mountain ranges rather than subducting into the mantle along an oceanic trench . An often - cited fact used to illustrate this process is that the summit of Mount Everest is made of marine limestone from this ancient ocean . </P>
when did the himalayan mountains start to form
when did the himalayan mountains start to form
About 50 million years ago
About 50 million years ago