Why Is It Important That We Have a Rigid Lithosphere

Why is it important that we have a rigid lithosphere overlying a weak asthenosphere?

A) If we did not have the rigid lithosphere and weak asthenosphere, the atmosphere would be very different with either too much ammonia and methane or too little oxygen and water.
B) If we did not have the rigid lithosphere and weak asthenosphere, we would be bombarded by cosmic rays that would strip away our atmosphere.
C) If we did not have the rigid lithosphere and weak asthenosphere, the earth would not have plate tectonics and would be covered entirely by water.
D) If we did not have the rigid lithosphere and weak asthenosphere, we would be bombarded by meteorites and we would not be able to hold the moon in orbit.