Question

The continental margins are relatively shallow because __________.

(a) they have been built up by sediments contributed by marine organisms
(b) the underlying crust is lighter
(c) they have been built up by sediment washed off of the continents
(d) they were formed in the last ice age, when the oceans were shallower
(e) sea level has dropped in the last 100 years

Answer 1

The continental margins are relatively shallow mainly because they are built up by sediments washed off of the continents and to a lesser extent by sediments from marine organisms, as well as the inherently higher elevation of the less dense continental crust.

Step-by-step explanation:

The continental margins are relatively shallow primarily because they have been built up by sediments washed off of the continents. The accumulation of sediment occurs particularly during episodes of low sea level when the continental shelf is exposed, allowing rivers and other erosive processes to transport large amounts of sediment to the continental edges. Additionally, in some areas, sediments can also be contributed by marine organisms, further building up the margin. The underlying continental crust, being composed of less dense materials such as granite, also plays a role as it rises higher on the mantle compared to the denser oceanic crust, contributing to shallow continental margins. Sediment deposition is affected by various processes across geological time scales, as in the case of the Coastal Plain formed post-Pangaea rifting.