How do shields differ from stable platforms? A) Shields only occur on continents, whereas stable platforms occur both on continents and on the ocean floor. B) Stable platforms are consistently older than local shields. C) Stable platforms only occur on continents, whereas shields occur both on continents and on the ocean floor. D) Shields consist of exposed igneous or metamorphic rock, whereas stable platforms are covered with a veneer of sedimentary rock. E) Stable platforms consist of exposed igneous or metamorphic rock, whereas shields are covered with a veneer of sedimentary rock.

What this question is really testing

Shields and stable platforms are both the ancient, stable cores of continents (parts of cratons). The difference is not mainly where they occur, but what rock is exposed at the surface.

What a shield is

A shield is an area where the old crystalline “basement” rocks are exposed.

• Rock type at the surface: mostly igneous and metamorphic rocks (Precambrian crystalline rocks)
• Little to no sedimentary cover

What a stable platform is

A stable platform has the same kind of crystalline basement, but it is buried.

• Rock type at the surface: a relatively thin “veneer” of sedimentary rock on top
• Crystalline basement is underneath, not exposed

Picking the correct choice

• D matches the definitions: exposed crystalline rocks in shields, sedimentary cover on stable platforms.
• A and C are wrong because both shields and stable platforms are continental features, not typical ocean-floor settings.
• B is wrong because platforms are not “consistently older”; both are ancient and can be similar ages.
• E reverses shield vs platform.