Question

which statement best describes the theory of plate tectonics?
plates sometimes move closer to one another.
sections of earth that shift are part of earths asthenosphere.
sections of earths continents are in slow, constant movement.
parts of the ocean floor move as they are carried by rift valleys.

Explanation:

1. Analyze Option A: Plates sometimes moving closer is part of plate tectonics (convergent boundaries), but it's a partial description.
2. Analyze Option B: Tectonic plates are part of the lithosphere (crust and upper mantle), not the asthenosphere (semi - molten layer below lithosphere), so this is incorrect.
3. Analyze Option C: The theory of plate tectonics states that the Earth's lithospheric plates (which include continental and oceanic crust) are in slow, constant movement due to convection currents in the mantle. This option accurately captures the core idea of plate tectonics.
4. Analyze Option D: Ocean floor movement is due to seafloor spreading at mid - ocean ridges, not being carried by rift valleys (rift valleys are formed by divergent boundaries on land or at mid - ocean ridges). This is an incorrect description.

Answer:

C. Sections of Earth’s continents are in slow, constant movement.