By the early twentieth century, geologists had numerous observations suggesting that in some parts of the world, the climates in the past had been very different from today's. Evidence included glacial deposits in areas that are now tropical and fossils of tropical plants in areas that are now very cold. What was German meteorologist Alfred Wegener's explanation for these observations?

A) Earth's north and south poles wander over time.
B) The tilt of Earth's axis changes slowly over time.
C) Earth's continents are not fixed but instead move slowly over Earth's surface.
D) New ocean crust forms at mid-ocean ridges while old cold ocean crust sinks back into the mantle.