Sedimentary rocks found high in the Himalayan Mountains have been found with fossils of clams and other marine life. What does this indicate about the origin of the Himalayan Mountains?

Fossils of clams and other marine life imply that the area that the Himalayan mountains inhabits was once a sea, an ocean, or at the very least covered by water.

70 million years ago, the India landmass collided with the Eurasian supercontinent, closing off the Tethys Ocean and pushing rock layers up to create the Himalayan mountain range.