asthenosphere
/æsˈθɛnəˌsfɪr/
noun
- The layer of the Earth's upper mantle, below the lithosphere, that is semi-fluid and allows tectonic plates to move.
- Earthquakes occur when stress builds up in the lithosphere above the asthenosphere.
- The asthenosphere is hot and soft, allowing the continents to drift slowly over millions of years.
- Scientists study the asthenosphere to understand how volcanic activity is connected to plate tectonics.