The asthenosphere is found within the upper mantle, specifically below the lithosphere.

Here's a breakdown:

* Earth's Structure: Earth's interior is made up of layers: crust, upper mantle, lower mantle, outer core, and inner core.

* Lithosphere: The rigid outer layer of Earth, including the crust and the uppermost part of the mantle.

* Asthenosphere: A semi-solid, partially molten layer within the upper mantle. It is located just below the lithosphere and is characterized by its ability to flow slowly over long periods.

* Lower Mantle: The solid, rigid layer below the asthenosphere.

So, the asthenosphere sits within the upper mantle, just below the lithosphere.