Final answer:
The lithosphere is most directly affected by earthquakes and volcanoes. Earthquakes result from plate tectonics and fault stress, while volcanoes occur from magma surfacing, reshaping Earth's crust.
Step-by-step explanation:
The lithosphere is the sphere of the Earth that is most directly affected by earthquakes and volcanoes. Earthquakes result from the movement of Earth's crustal plates and the release of stress that has accumulated along geological faults. Volcanic eruptions occur when magma from within the Earth's mantle makes its way to the surface.
The lithosphere encompasses the crust and the upper part of the mantle, which are broken into tectonic plates. These plates can move, collide, or slide past each other at their boundaries, leading to earthquakes. Volcanoes are primarily formed where these plates diverge or converge, allowing magma to escape to the surface. Both of these geological activities can reshape the Earth's surface and have profound effects on topography and ecosystems.
The other spheres of the Earth, the atmosphere, hydrosphere, and biosphere, can also be affected by these events, but the lithosphere is the primary sphere where the processes originate and have the most immediate impact.