Final answer:
Darwin thought that inactive volcanic seamounts would sink into the ocean over time due to geological processes such as plate tectonics and sediment accumulation.Option 1 is the correct answer.
Step-by-step explanation:
Charles Darwin believed that inactive volcanic seamounts on top of the oceanic crust would sink deeper into the ocean over time due to processes such as continental drift and the gradual accumulation of sediments.
This sinking is related to tectonic plate movements and the lifecycle of volcanoes, which begin as active eruptions due to mantle hotspots, then gradually become dormant and erode away, ultimately submerging as they become denser and the oceanic crust cools and contracts.