Here's a breakdown:

* Lithosphere: The rigid, outermost layer of Earth, composed of the crust and the uppermost part of the mantle. It's broken into tectonic plates that move on top of the asthenosphere.

* Asthenosphere: A layer of the upper mantle located below the lithosphere. It's characterized by being partially molten, allowing it to behave more like a viscous fluid than a solid. This fluidity allows the tectonic plates to move on top of it.

Key Differences:

* Strength: The lithosphere is strong and rigid, while the asthenosphere is weaker and more ductile.

* Temperature: The asthenosphere is hotter than the lithosphere, contributing to its partially molten state.

* Role in Plate Tectonics: The asthenosphere acts as a lubricant, allowing the tectonic plates of the lithosphere to move and interact, driving phenomena like earthquakes, volcanoes, and mountain formation.

So, the asthenosphere is the crucial "soft" layer beneath the rigid lithosphere, allowing Earth's tectonic plates to move and shape our planet's surface.