The crust is one of the three main concentric layers that make up the Earth's interior. It is a very thin layer of solid rock that forms the outermost shell of the planet and is home to living organisms as well as natural surface features such as rivers, lakes and mountains. The crust is significantly thinner than the core and the mantle (the other two main layers making up the Earth's interior). In fact, the crust represents less than 1% of the Earth's total volume. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Properties and composition The crust not only varies in thickness compared to other concentric layers, but also differs due to its properties and composition. The solid crust is not only significantly thinner than the other layers, but it is also less dense and less warm. Due to its solid nature, relative thinness and low density, the crust is brittle and prone to cracking. Additionally, the thickness of the crust is also not uniform, with some of its regions being thinner (1 km thick) and other regions having a thickness greater than 80 km. The crust is made up of a mixture of chemical elements, minerals and rock types. The most abundant elements present in the crust are oxygen, silicon, aluminum and iron. Other elements such as calcium, sodium, potassium and magnesium are also present, but in smaller amounts. Elements in the crust often combine with each other to form various compounds. Such compounds give rise to minerals. Minerals are the building blocks of rock. By definition, minerals are naturally occurring inorganic solids with defined chemical compositions and well-ordered internal structures. Minerals are generally composed of two or more elements. The crust is made up of more than 2000 different minerals. However, many of them are present in very small quantities. In fact, the crust is mainly composed of six minerals which are feldspar, quartz, pyroxene amphibole, mica and olivine. Feldspar is the most abundant mineral found in the crust. It consists of silicon, oxygen and other metallic elements such as sodium, potassium, calcium and aluminum. Feldspar can exist in different varieties depending on the metallic element present. There are two main types of feldspar, called plagioclase and alkali feldspar. This mineral has a light cream to salmon pink color. The second most abundant mineral is quartz. Quartz is one of the main components of granite and sand. It is a hard, water-insoluble mineral, consisting mainly of silica (SiO2). Quartz is usually colorless or white. Other minerals such as pyroxene, amphibole, mica and olivine are also present, but in smaller quantities. Minerals present in the crust (mainly feldspar and quartz) mix to form different types of rocks. Rocks can be classified into three groups: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rock is the most abundant type of rock in the Earth's crust. Rocks of this type form when molten rocks such as magma or lava cool and solidify. Igneous rocks are sometimes called "primary rocks" or "parents of all rocks" because they formed the Earth's first crust and gave rise to all other types of rock. Igneous rocks can be classified as intrusive or extrusive depending on theirtheir mode of formation and their occurrence. Intrusive rocks are rocks that form when magma solidifies beneath the Earth's surface. Some examples of this rock type include granite, diorite and gabbro. Extrusive rocks, on the other hand, refer to rocks that form when lava cools on the Earth's surface. These rocks include basalt, andesite and rhyolite. Sedimentary rocks form from the accumulation of sediment and organic matter. The sediments come from weathered or eroded pre-existing igneous or metamorphic rocks. When sediment builds up, the increased pressure causes the sediment to compress and form sedimentary rock. This process is known as lithification. Sedimentary rocks are found primarily in the upper parts of the crust because these types of rocks are not very stable at high temperatures and pressures. Some examples of sedimentary rocks are shale, sandstone, and limestone. Metamorphic rock refers to rock that forms when igneous or sedimentary rocks undergo changes in their structure due to high pressure and temperatures. The influence of heat and pressure causes the recrystallization and reorganization of molecules within the original rocks, resulting in overall changes in the hardness and color of the rocks. This process is known as metamorphism. This explains why sedimentary rocks are not very stable in the lower parts of the crust. Examples of metamorphic rocks include marble (from limestone), quartzite (from sandstone), and blue schist (from basalt). Different Types of Crust Crust can be divided into two types: continental crust and oceanic crust. In general, continental crust is the part of the crust that gives rise to continents, while oceanic crust is the part of the crust that lies beneath Earth's oceans. These types of crusts differ from each other in thickness, density and composition. The continental crust covers about 40% of the planet. This type of crust is mainly exposed to air. It is older and thicker than the oceanic crust. In fact, the continental crust is about 2 billion years old and has an average thickness of 35 to 40 km. The rocks of the continental crust are sometimes called "Sial" by some geologists. This is because the continental crust is primarily composed of granite, the most abundant chemicals of which are silica (SiO2) and alumina (AlO3). Continental crust contains a greater amount of oxygen than oceanic crust. This is because the continental crust is more exposed to the atmosphere. Due to the chemical composition of granitic rocks, continental crust has a relatively low density compared to oceanic crust. In fact, continental crust has an average density of 2.7 to 3.0 g/cm3. In terms of minerals, the continental crust can be described as felsic since the most abundant minerals in granite are feldspar and quartz, while minerals such as amphibole, pyroxene and olivine are only present. 'in trace form. Oceanic crust covers about 60% of the planet. This type of crust is thin and relatively young. Its thickness does not exceed about 20 km and has an average thickness of 7 to 10 km. Moreover, it is no more than 180 million years old (approximately). The old oceanic crust is destroyed at subduction zones. Oceanic crust forms at mid-ocean ridges as a result of the process of seafloor spreading during which plates are separated. Thatcauses the release of pressure in the underlying mantle. Such pressure melts part of the peridotite (igneous rock present in the mantle). Melted peridotite gives rise to basaltic lava which rises, cools, solidifies and forms new oceanic crust. Oceanic crust is denser than continental crust since it is mainly composed of basalt. This type of crust has an average density of 3.0 to 3.3 g/cm3. Basalt rocks are sometimes called "Sima" by geologists because of the presence of silica and magnesium. In mineral terms, basalt is considered a mafic rock because feldspar, amphibole, and pyroxene are the most abundant minerals present. The Moho discontinuity There is a boundary between the crust and the upper part of the mantle. This boundary is called the Moho discontinuity and is named after Andrija Mohorovicic, the seismologist who discovered it. Mohorovicic discovered a marked discontinuity in which P- and S-wave velocities increased abruptly. He understood that there was a relationship between the speed of seismic waves and the density of the material moved by the waves through and so he interpreted this discontinuity as a compositional change within our planet. He concluded that this sharp increase in seismic wave speed is due to the presence of a low-density crust over a high-density mantle. The lithosphere The crust and the rigid upper part of the mantle together form what is called the lithosphere. The lithosphere is subdivided into several plates. The lithosphere is made up of 7 major plates and several minor plates. These plates sit at the top of the asthenosphere (the softest and least rigid layer of the mantle). The plates move under the effect of convection currents generated when magma rises and falls in this part of the mantle. Plate movement is responsible for both the creation and destruction of the crust as well as many volcanic and seismic activities. Plate boundaries Adjacent plates can interact with each other in different ways, giving rise to different plate boundaries. Plate boundaries are classified into three types: divergent boundaries, convergent boundaries, or transform faults. The type of boundary depends on the direction in which adjacent plates are moving. With divergent boundaries, two plates move away from each other in opposite directions. When two adjacent ocean plates move apart during the process of seafloor spreading, magma beneath the plates rises, cools, and solidifies to form new crust. This type of boundary is found on mid-ocean ridges such as the Mid-Atlantic Ridge (the boundary between the North American Plate and the Eurasian Plate). The formation of shield volcanoes or volcanic islands like Iceland is common at this type of boundary. When continental plates move apart, the tensional forces generated when the plates separate cause cracks and faults to appear in the crust. As the plates continue to move apart, the rock between the faults pushes downward to form what is called a rift valley. An example of a Rift Valley is the East African Rift Valley in Kenya, Africa. Convergent boundaries involve the movement of two plates against each other. When oceanic crust converges with continental crust, the thicker, denser oceanic crust sinks beneath the thinner, less dense continental crust into the mantle by subduction to form a subduction zone. As the crust subducts, heat, pressure.