Geology 330 - the Earth

        The Earth is a planet in our solar system in whch two types of planets Terrestrial and Jovian are found. It was created according to the Nebular Hypothesis, through a formation of two planetary rings, inner and outer. The rings contains different materials thus creating two types of planets small, hot and mainly composed of Iron: Terrestrial and large, cold and containing hydrogen: Jovian. Through the knowledge of the Nebula hypothesis we will focus on planet Earth to understand the specificity and singularity of it.

        As we know, the planetary rings made the formation of planet Earth possible through the collision of materials leading to the formation of planets. These materials were the metallic meteorites composed of iron; the stony meteorites constituted of rock fragments and last the comets transporting icy fragments, which produced water on Earth. All these materials impacted with Earth creating energy.
        The heat energy on earth is and was transferred into its center through three processes. The first one is the impact energy; the impact of materials creates a kinetic energy that is converted into heat energy. Most of these impacts occurred in the Earth’s early evolution. Another one was the gravitational energy; through the contraction of Earth it generates heat energy stored in the core. And finally the radioactive energy, which is a slow transformation of a parent into daughter producing heat energy as a byproduct. All these processes made the Earth’s interior rise high enough to melt and become ordered. Instead of being a random mix of fragments, it is a differentiation of nested layers.
        Each layer can be linked to the derivation of heat energy. First, the core is the center of earth and composed of iron. It is split in two parts, the inner core and the outer core; the inner core is solid iron whereas the outer core is liquid iron. The inner core is high in temperature but due to the high pressure it is solid. The high pressure of early evolution and the impacts of Fe-meteorites made the iron “drops” accumulate towards the center. However, the silicates minerals migrated upwards through convection, and were present in the mantle composed of dense rock (iron and magnesium silicates) or in the oceanic crust under molten form. The mantle is related to the stony meteorites colliding with Earth in the early evolution. The upper mantle has two specific layers: the lithosphere and the asthenosphere. These two layers have a specific role on the surface of earth with the movement of plate tectonics. The lithosphere is cold and rigid sphere of rock where the asthenosphere is hot, weak and mobile. The last layer is the crust and has a low-density rock only 5-70 km. There is two types of crust, first the oceanic crust, which is composed of basalt, generally thin and dense only 7km and is the result of silicates that moves from the core to the surface. Secondly, the continental crust is similar to granite, which make it thicker and lighter than the oceanic crust. The differentiation caused the heavy metals (iron, nickel,) to be concentrated in the core of earth, whereas the light elements (oxygen, silicon, aluminum, potassium or sodium) were enriched in an outer layer of the earth that is now termed the mantle and the crust.
        
        The differentiation into nested layers was needed to produce life. Through convection, conduction and radiation sources of energy always have been present on Earth. When iron was melting high enough, it formed the initial atmosphere and hydrosphere two main elements for life. Furthermore, volcanic activity released gases, which developed the atmosphere and hydrosphere however it would of not contain any or little oxygen, thus taking a certain time to support life. By the process of convection, many things happened such as plate tectonics, mountains building, recycling materials.  All of these processes help to form life and allow an evolution.