Question: The lithosphere includes Earth's crust and the uppermost part of the mantle, forming the rigid outer shell of the planet. Which of the following best represents a plausible thickness for the lithosphere? Need Assignment Help? Option A While some parts of the lithosphere may be relatively thin, a thickness of about 15 miles is a reasonable estimate. Option B A thickness of approximately 100 miles is a reasonable estimate for the lithosphere, which includes both the crust and the uppermost solid mantle. Option C The lithosphere is estimated to be about 600 miles thick. Option D A thickness of 350 miles would be a reasonable estimate for the lithosphere.