Geological Formation of the Earth

Within the Earth, heat energy is derived from three separate processes: extraterrestrial impacts from materials in the rings surrounding the proto-planet (iron meteorites, stony meteorites, and comets), gravitational contraction occurring within the Earth, and the decay of unstable radioactive isotopes. Extraterrestrial impact was a primary factor in the derivation of heat energy during the planet’s accretion, since the immense kinetic energy present in the collisions was converted immediately to heat energy when the extraterrestrial bodies impacted the Earth. Gravitational contraction was also a factor during planetary accretion, as the slow compaction of the earth converted gravitational energy into heat energy that stayed trapped within the Earth’s crust due to rock’s ineffectiveness as a conductor of heat. Radioactive decay releases heat energy as well, due to the constant reactions present in the breaking down of unstable elements. In the early Earth, a greater number of both unstable radioactive elements and extraterrestrial impacts combined with more dramatic gravitational crowding led to an internal heat content that has gone unmatched over time.

The three types of interstellar materials found in the universe that combined to eventually form the earth were iron meteorites, stony meteorites, and comets. As these three materials collided and merged together while the Earth was generating heat energy at a more rapid rate, melting occurred. Once in liquid form, the three types of materials separated by weight to form distinct layers. The metals sank to the center of the earth, the rocky materials floated closer to the surface, and the ice and other comet-derived materials either melted or evaporated, leading to the creation of both early oceans and the atmosphere.

Within the Earth, there are four main layers: the inner core, the outer core, the mantle, and the crust. The inner core is derived from the collision of iron- and nickel-heavy meteorites with the young Earth, and is solid and densely packed. The outer core surrounds the inner core, and is mainly comprised of molten iron. This layer, too, was created as a result of the increased impact of metallic meteorites during the Earth’s formation. The mantle is mostly molten, but is composed of rocky materials left over from extraterrestrial collision as opposed to metallic ones. The mantle is subdivided into the asthenosphere, which holds hot, weak, gradually flowing material, and the lithosphere, which is rigid and the coolest of the internal layers. The lithosphere also edges into the crust, which is solid and comprised almost exclusively of rocks of all different varieties. The crust is also subdivided due to the stratification of Earth’s layers in its formation, with rock comprising the oceanic crust being more basaltic in nature than the rock types found in the continental crust, which is more granite-like in its composition. The two outer layers of the earth, the hydrosphere and the atmosphere, found its origins in the vaporization of icy elements derived from the collision of comets with the Earth. The hydrosphere, covering 71% of the Earth’s surface, is comprised of water, initially from comets that melted in the intense heat borne out of Earth’s formation. The atmosphere was formed by both the gases present in the comets that were released in the melting process, and by emissions created by increased volcanic activity on the young Earth. Without the accretion of metallic, rocky, and icy extraterrestrial bodies during Earth’s formation and the subsequent stratification of the different types of elements present, the Earth would have a very different makeup.