What type of layer constitutes the upper part of the lithosphere?

The upper part of the lithosphere is constituted by the crust. The lithosphere itself is the rigid outer layer of the Earth, which includes both the crust and the uppermost part of the mantle. The crust is the layer that forms the continents and the ocean floors, providing a solid foundation for landforms and geological features. It varies in thickness and composition, generally being thicker beneath continents and thinner beneath oceans.

While the atmosphere encompasses the layers of gases surrounding the planet, the core is the innermost layer of the Earth, composed mainly of iron and nickel, and the hydrosphere refers to all the water present on Earth, including oceans, rivers, and lakes, but does not form any part of the lithosphere. Therefore, the crust is specifically designated as the top layer of the lithosphere, making it the correct choice.