* Pressure: The immense pressure from the weight of the entire Earth above compresses the mantle rock, making it denser.
* Temperature: While temperature generally increases with depth, the base of the mantle is still relatively cool compared to the core. This means the rock is denser than it would be if it were hotter.
* Composition: The lower mantle is primarily composed of silicate minerals like bridgmanite and ferropericlase, which are denser than the minerals found in the upper mantle.
In summary, the combination of high pressure, relatively cooler temperatures, and denser mineral composition makes the base of the mantle the densest part of the mantle.
