marine fossils means fossils of marine animals & marine animals are water animals ->  marine fossils are fossils of water animals  marine fossils are fossils of water animals & marine fossils are found in mountains ->  fossils of water animals are found in mountains  fossils of water animals are found in mountains & if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past ->  the mountains used to be covered by water in the past  the mountains used to be covered by water in the past & a mountain is a kind of environment & if something used to be in the past then that something has changed & a body of water is a kind of environment -> the environment has changed from a body of water to mountains