The Grand Canyon was once covered by an ocean. The evidence for this can be found in the composition of the rocks and the presence of stromatolites.
The rocks in the Grand Canyon Supergroup, which is the oldest set of rocks in the canyon, are primarily composed of sandstone. Sandstone is a type of sedimentary rock that forms in environments such as beaches and shallow seas. The presence of sandstone in the Grand Canyon Supergroup suggests that this area was once a very shallow sea.
Additionally, stromatolites have been found in the Grand Canyon Supergroup. Stromatolites are layered structures formed by the growth of microbial mats, typically in shallow marine environments. They are one of the earliest forms of life on Earth and are commonly found in rocks that were once covered by oceans. The presence of stromatolites in the Grand Canyon Supergroup further supports the idea that this area was once a sea.
Furthermore, the rock layers in the Grand Canyon Supergroup have been tilted, whereas the rocks above this set are horizontal. This is known as an angular unconformity. Angular unconformities are typically formed when tectonic forces cause the rocks to be uplifted and tilted, and then erosion occurs, exposing the tilted rocks to the surface. The fact that the rocks in the Grand Canyon Supergroup are tilted suggests that they were once deposited horizontally in a marine environment and were subsequently uplifted and tilted.
The composition of the rocks and the presence of stromatolites indicate that the Grand Canyon was once covered by an ocean. The tilted rock layers in the Grand Canyon Supergroup further support this idea.