The asthenosphere is more rigid and dense than the lower mantle because of the temperature and pressure differences. The asthenosphere is located closer to the surface of the Earth and is therefore subjected to higher temperatures and lower pressures. This makes the rocks in the asthenosphere more pliable and less dense than the rocks in the lower mantle. Additionally, the lower mantle is composed primarily of solid rock, while the asthenosphere is composed primarily of molten rock. This also contributes to the lower mantle being more rigid and dense than the asthenosphere.
