Lower Mantle

The lower mantle is one of the five geological layers of Earth. It is different from the other geological layers of the Earth, being the site of molten rocks that are ejected to the surface through volcanoes. Although it is also molten rocks, it is more solid than the upper mantle as it flows very slowly, like a very dense liquid.

The main process that helps shape the planet take place in the lower mantle, playing an important role in creating volcanoes. Hot convection forces in this layer cause molten rocks and mineral to boil so intensely that they explode through the Earth’s crust, giving birth to volcanoes and the formation of rock islands in the oceans (Pacific).

Characteristics

The lower mantle is the thickest continuous layer of the Earth’s as it constitutes more than 50% of its size and the 70% of the planet’s mass. It measures about 1,550 miles (2,500 km) thick, having an estimated temperature of 4,000° F (2,204° C). It is believed that this layer is made mostly of magnesium, silicon, and oxygen, with smaller amount of iron, calcium, and aluminum. Combined together, these elements form a rare mineral called perovskite.

The age of the lower mantle is hard to figure out, simply because its molten rocks cannot be reached to take a sample and study it. However, since this layer was formed very early in the geological history of the Earth, it is probably billions of years old. At the same time, the lower mantle’s rocks change their form slowly and regularly as the layer convects and boils, with older rocks changing into new, younger ones.

You must remember that convection is the propagation of heat in a liquid. Hot melted rock is less dense and lighter than cooler molten rock, which is more dense and heavier. As the hotter lighter rock rises up to the top, the cooler and dense one sinks down.

Below, diagram of the Earth geological layers, showing the upper and lower mantle.