¢ Looking at the lower mantle, its chemical omposition includes silicon, magnesium, and oxygen. Most likely, it probably also contains some iron, calcium, and aluminum. This layer is comprised of 72.9% of the antle-crust mass, making the Earth abundant in the chemical elements of silicon, magnesium and oxygen, the layers primary components.
¢ 3. Higher up, we encounter the upper mantle. Through excavations in volcanoes, scientists have found that this part of the crust composes of 15.3% of the total mantle-crust mass and is made of crystalline forms of Olivine (Mg,Fe)2SiO4 and pyroxene (Mg,Fe)SiO3. The upper mantle makes up 10.3% of the Earths mass, extending a depth of 6-250 miles (10-400 kilometers). A relatively large portion when compared to the other interior layers. This layer is not completely made of solid minerals for scientists speculate that the asthenosphere could be partly liquid molten.
¢ D: The D layer of Earth is about 3% of Earths mass, is 125 to 188 miles (200 to 300 kilometers) thick and covers about 4% of the mantle-crust mass. This layer, in terms of whether it is part of the lower mantle or an independent layer is still somewhat unclear. Based on evidence collected from seismic discontinuities, the D layer might differ in chemical composition from the lower mantle above it.
¢ The next layer, the Transition region comprises 7.5% of Earths mass with a depth of 250-406 miles (400-650 kilometers). This layer is also known as the mesosphere and is 11.1% of the mantle-crust. It is made of mainly basaltic magmas with amounts of calcium, aluminum and garnet (an aluminum-bearing silicate mineral). The layer becomes dense when the garnet mineral cools but is buoyant and light when subject to heat due to the low melting points.
¢ The outer most layer, the crust, is categorized into two parts, the Oceanic crust and the continental crust. The Oceanic crust is the smallest part of Earth, only 0.099% of its mass and reaching a small depth of 0-6 miles (0-10 kilometers). In the beginning of time, it was possible that this area did not exist for through frequent volcanic activity does only the crust form. Evidence of this is marked by the oceanic ridge system, which is a 25,000 mile (40,000-kilometer) array of many volcanoes which creates layer after layer of new crust at the rate of 17 km3 per year. The ocean floor is covered in basalt originating from volcanic activity and as a matter of fact, Iceland and Hawaii are two island systems that emerged from the accumulated basalt.
¢ Continental crust: The second smallest area of the Earth is the Continental crust, making up only 0.374% of the Earths mass and extending a short depth of 0 31 miles (0-50 kilometers). Looking at the percent by composition, the continental crust makes up only 0.554% of the mantle-crust mass. The layer is composed primarily of crystalline rocks made of low-density buoyant minerals dominated mostly by quartz (SiO2) and feldspars (metal-poor silicates). This is the outer part of the Earth composed essentially of crystalline rocks. The continental crust and the oceanic crust are also referred to as the lithosphere because of the cool and rocky conditions that exist in its