Final answer:
The statement that the surface of a mountain was once under the sea is true, as evidenced by marine fossils found on mountains. These fossils, combined with stratigraphic evidence in the rock layers, support the idea of an Earth that has undergone significant changes, including fluctuations in sea levels.
Step-by-step explanation:
The evidence that the surface of a mountain was once under the sea is indeed true. This is supported by the presence of marine fossils on the mountain, which are remnants of ancient sea life found far from current oceans. Moreover, many layers of rock on Earth represent the order in which rocks and fossils appeared, allowing scientists to trace back the history of our planet and the life on it. Such finds include fossils of bivalves and trilobites, as well as indications of past geological events like volcanic eruptions, earthquakes, and erosion that have shaped the Earth's surface over time.
Furthermore, scientists have discovered evidence in the form of fossilized microbial mats dating back to approximately 3.5 billion years ago. These finds suggest substantial changes over Earth's history, including that land now dry and elevated as mountains was once submerged under sea level. Additionally, sedimentary layers provide clues like the presence of bivalves, coral chips, and even partial imprints of trilobites, which are indicative of past marine environments now uplifted through geologic processes. Overall, such fossils and other geological evidence suggest a dynamic and changing Earth where sea levels have fluctuated significantly over time.