Which statement best describes the lithosphere's mechanical behavior?

Which statement best describes the lithosphere's mechanical behavior?

• A. It is rigid and behaves as a solid shell
• B. It flows like a liquid beneath the surface
• C. It is entirely molten
• D. It is the Earth's inner core

Answer: (A)

The lithosphere behaves as a rigid outer shell. It includes the crust and the rigid portion of the upper mantle, and its cooler, stronger rocks resist flow on geological timescales. That rigidity lets it act as separate plates that move as units, collide, pull apart, or slide past each other at plate boundaries. Beneath it, the asthenosphere is hotter and weaker, able to flow slowly, which is why tectonic plates ride on top rather than the lithosphere itself behaving like a liquid. The other statements describe deeper or different layers: a liquid flow beneath the surface refers to the partially molten asthenosphere, not the lithosphere; being entirely molten is not accurate for the lithosphere; and the inner core is a separate, deeper layer, not the lithosphere.

The lithosphere behaves as a rigid outer shell. It includes the crust and the rigid portion of the upper mantle, and its cooler, stronger rocks resist flow on geological timescales. That rigidity lets it act as separate plates that move as units, collide, pull apart, or slide past each other at plate boundaries. Beneath it, the asthenosphere is hotter and weaker, able to flow slowly, which is why tectonic plates ride on top rather than the lithosphere itself behaving like a liquid. The other statements describe deeper or different layers: a liquid flow beneath the surface refers to the partially molten asthenosphere, not the lithosphere; being entirely molten is not accurate for the lithosphere; and the inner core is a separate, deeper layer, not the lithosphere.