6. What is \( \# 4 \) ? (Underneath layer \( \# 3 \) ) \( \begin{array}{ll}\text { A) Lithosphere } & \text { C) Asthenosphere } \\ \text { B) Crust } & \text { D) Mantle }\end{array} \)

The lithosphere is the outermost layer of the Earth, encompassing the crust and the uppermost solid part of the mantle. It's rigid and is broken into tectonic plates that float on the semi-fluid asthenosphere beneath. This layer is crucial for supporting life as it includes landforms, soils, and the ocean floor. Just below the lithosphere lies the asthenosphere, which is like a hot, melted layer of the mantle that allows tectonic plates to move. This movement is responsible for many geological phenomena such as earthquakes and volcanic eruptions. The asthenosphere doesn’t behave like a typical solid; instead, it acts more like a viscous fluid over geological time, enabling the dynamic nature of our planet’s surface.