Question

Researchers in the 1940s found that sediment on the seafloor was thinner than expected. How did this provide evidence for continental drift?

Because this seafloor was relatively old, the sediment had turned to rock.
Because this seafloor was relatively young, there had been less time for sediment to accumulate.
The motion of the continents caused sediment to fall away from the seafloor.
The motion of the continents caused sediment to be ground up into smaller pieces.

Answer 1

The last option is the correct answer. Motion of the massive continents and the movement of water over time can grind the sediment into fine particulate. This would register with us as sand or some other material rather than sediment.

Answer 2

Answer

The motion of the continents caused sediments to be ground up into smaller pieces

Explanation

It is in order to say that tectonic plates are in constant motion, and when one slides beneath the other it carries with it the sediments present on the ocean floor. The subduction of the lithosphere is therefore a way by which sediments are removed from the ocean floor. There are more sediments present in the ocean floor as compared to the original thickness.