The Earth’s crust, one of three main concentric layer that makes up its interior, is the crust. This is a thin, solid layer of rock that makes up the outer shell of Earth. It supports living organisms and natural features such as rivers or lakes. The Crust has a thickness that is less than the core (the Earth’s main layer) and the mantle. In fact, less than 1 percent of earth’s total volume is made up of crust.
Properties and composition. The crust’s thickness varies between the concentric layers. However, it also differs due its properties and composition. The solid layer is much thinner than the rest of the layers. It is also denser and hotter. Because of its solid nature, it is relatively thin and low in density, making the crust brittle. The crust also differs in thickness. Some regions are thinner by 1 km while others are thicker by 80 km. The crust is made up of various chemical elements, minerals, as well as different types of rock. The crust is composed of iron, silicon, oxygen, and aluminium. Although other elements like magnesium, calcium, sodium or potassium are present, they are less abundant. These elements can often be found mixed with each other to form different compounds. Minerals are formed when such compounds are combined. Minerals form the basis of rock. Minerals are organic solids found naturally and have well-ordered internal structure. Minerals usually contain two or three elements. Over 2000 minerals make up the crust. Many of these minerals are only found in small amounts. It is actually composed of six minerals: quartz, feldspar amphibole (pyroxene), mica, and Olivine. The crust’s most abundant mineral is feldspar. It is made up of silicon and oxygen. There may be different types of Feldspar depending on the metal element present.
There are two main types feldspars: alkali and plagioclase. This mineral is light pink to salmon-pink in color. Quartz is second in mineral abundance. Quartz is a primary component of granites and sands. Quartz is a water-insoluble, hard mineral that mainly contains silica. Quartz is generally colorless to white. However, other minerals like olivine, amphibole and mica are also found in small amounts. The crust’s minerals, feldspar and mostly quartz, combine to create different types of rock. There are three types of rocks: igneous, sedimentary, and metamorphic. The most common rock type in Earth’s crust is igneous rock. This type of rock forms when magma and lava cool and solidify. The ‘primary rock’ or ‘parents all rocks’ are also known as igneous rocks. They were responsible for the formation of the Earth’s initial crust and all subsequent types of rock. You can classify igneous rocks as either intrusive, or extrusive depending on how they formed and when they occur. Intrusive rock is a rock that forms when magma solidifies under the earth’s crust. Granite, gabbro, and diorite are just a few examples.
Extrusive Rocks, on one hand, refers to rocks that form as lava cools on earth’s surface. Basalt, andesite, rhyolite, and others are examples of such rocks. Organic matter and sediment can create sedimentary rock. Sediments can be formed from weathered, eroded and/or eroded metamorphic or igneous rock. Sediments form when sediments build up and are compressed by increased pressure. This is called Lithification. These sedimentary rocks can be found mostly in the crust’s uppermost parts, as they are less stable at high temperatures or high pressure. Examples of sedimentary rocks include shale and sandstone as well as limestone.
Metamorphic rocks are formed when sedimentary or igneous rocks undergo structural changes due to high pressure and high temperature. Rerystallization occurs when molecules in original rocks are reorganized by heat and pressure. This causes overall changes in rock hardness and color. Metamorphism is the name of this process. This is why sedimentary rocks are not stable in the lower crust. Metamorphic rocks include blueschist, quartzite and marble. There are two types:
Both oceanic and continental crust. The crust that forms the continents is called continental crust. Oceanic crust, on the other hand, is the crust under which the oceans are formed. They differ in thickness, density, and composition. The planet’s 40% is covered in continental crust. This crust type is mostly exposed. It is thicker and older than the oceanic crust. The continental crust, which is an average of 35-40km thick, is about 2 billion years in age. Geologists sometimes refer to the rocks that make up continental crust as “Sial.” Because of the high concentrations of silica (SiO2) in granite, the continental crust is composed mainly of granite.
Oceanic crust contains less oxygen than continental crust. This is because continental crust has more exposure to the atmospheric environment. The continental crust is relatively dense compared to oceanic because of its chemical composition. The continental crust actually has a density of between 2.7-3.0g/cm3. It is classified as felsic for its minerals. The most abundant minerals found in granite are feldspar, quartz, and olivine. Around 60% of the globe is covered by oceanic crater. This crust type is relatively young and thin. It is approximately 20km thick, and averages 7-10km in thickness. It is approximately 180 million year old.
Subduction zones destroy the oceanic crust. Subduction zones are the place where oceanic ridges form. This causes pressure to escape from the underlying crust. The pressure causes some of the mantle’s peridotite to melt (igneous rocks). Basaltic lava is formed when peridotite melts. It rises, cools and solidifies, forming an oceanic crust. Because it is mostly composed of basalt, oceanic crust is denser that continental crust. This crust averages 3.0-3.3 g/cm3. Geologists sometimes call basaltic rocks “Sima” because they contain silica, magnesium, and other minerals. Basalt is often referred to as a mafic or mafic rock because of its abundance of silica, amphibole, pyroxene and feldspar. The Moho’”discontinuity. A boundary exists between crust and upper mantle. This boundary is known as The Mohodiscontinuity. Named after Andrija Mohorovicic a seismologist, it is also called the Moho. Mohorovicic found a discontinuity in which the velocity of S-waves (and P-waves) increased abruptly. He realized that seismic waves velocity and density are related and therefore interpreted the discontinuity as a change to our planet’s composition. He believed that the sharp rise in seismic wave velocity could be due to a low density crust over a dense mantle. The Lithosphere. The lithosphere is made up of the crust and the top portion of the mantle. There are many plates that make up the lithosphere.
The lithosphere consists of seven major plates and several smaller plates. These plates are found on top the asthenosphere, which is the less rigid and softened layer of mantle. Convection currents are what cause the plates’ movement. Creation and destruction of crust, as well as many volcanic and seismic events are all caused by the movement plates. Plate Boundaries Plate boundaries can be created when adjacent plates interact in different ways, resulting in different plate boundaries. The three main types of plate boundaries can be classified as divergent boundaries, transform faults or convergent borders. The direction the plates are moving in determines the type and location of the boundary. When two plates are moving in different directions, they will have divergent boundaries. Two adjacent oceanic islands are broken up by seafloor spread. This causes the magma beneath them to rise, cool, and solidify to create the new crust. This type boundary is found on mid-ocean Ridges like the Mid-Atlantic Ridge. (The boundary between North American plates and the Eurasianplate).
This type is known for the formation volcanic islands and shield volcanoes. Cracks and faults can form within the crust when continental plates are separated by the tension created by the plates breaking apart. Rock between faults is pushed apart by the plates, creating what’s known as a “rift valley”.
East African Rift Valley is an example. It can be found in Kenya, Africa. Convergent boundaries refer to the movement between two plates. When oceanic and continental crusts converge, the thicker, heavier oceanic layer sinks below the denser continental crust into the subduction zone. The crust melts to magma under pressure and heat as it subducts. This magma rises out of cracks in your crust, and can create composite volcanoes.
This type of boundary is prone to earthquake and volcanic activity. The subduction of the Pacific Plate as it converges to the Eurasian is an example of such a boundary. Because the densities of the two plates are similar, they don’t sink down each other when they converge. The plates pushing into one another push the sediment overlying them upwards, creating fold mountains. For volcanic eruptions, magma is also capable of rising through cracks between plates. Examples of fold mountains are the Himalayas and Andes mountain chain. A type of plate boundary that prevents crust from being created or destroyed is called transform faults. This boundary allows two plates to move in opposite directions. Two plates sliding past each other causes friction to cause them to become stuck. This causes pressure to build up between them.
The pressure eventually releases in the form a earthquake. This kind of boundary can be seen in the San Andreas Fault. Despite its small size, the crust plays an important function in supporting all living creatures. There are two kinds of crust. Each has its own chemical composition and different properties. The crust forms part of lithosphere and is responsible for plates and tectonic activities such as earthquakes, volcanoes, and tsunamis.
