Unit 3.1: Crust

• Until today, only a very small portion of Earth is explored by humans
• More than 95% of the bulk of the planet remained a mystery until the emergence of the study of waves produced during the planet’s ground shaking.
• Earth is divided into three layers: the rigid crust where living things live in, a mantle which can be further divided into layers, liquid outer core, and a solid inner core.
• Inner planets or the Earth-like planets are also believed to have similar internal structures.
• Terrestrial Planets


  are rocky planets. These include Mercury, Venus, Earth, and Mars.
• Earth’s differentiation refers to the process of forming layers of the planet due to gravity and density differences of materials during its early formation. Heavy elements sank to the center while others floated near the surface.
• The crust is the outermost layer of the geosphere
• Cruste. It is made up mostly of solid rocks and minerals and is enriched in silica and other components. It is extremely thin, compared to the other layers, and its thickness varies from 5 to around 80 km depending on where you are on the planet.
• Crust accounts to <1% of Earth’s total volume.
• Mohorovičić discontinuity.


  boundary between the crust and mantle
• The crust, together with the uppermost part of the mantle, make up the brittle lithosphere, which is broken up into major sections called tectonic plates.
• Tectonic Plates


  These plates are in constant motion relative to each other and bounded by tectonically active plate boundaries. These are irregularly shaped slabs of rock that float on top of the asthenosphere.
• The abundance of elements on the crust was studied using its rock.
• . Oxygen, silicon, aluminum, and iron are abundant elements found on Earth’s crust
• The most abundant element in Earth’s crust is oxygen with an average abundance of 276 900 ppm (parts per million).
• Oxygen


  combines with silicates, carbonates, and phosphates in which it serves as a major elemental component. It has several purposes to society such as in industries, medicine, and commercial purposes.
• Silicon, being the second most common element, exists as a compound in the mantle and crust.
• Silicon


  is found in sand, quartzite, mica, and talc. This element is usually utilized in the production of ceramics, glass, cosmetics, insecticides, and pharmaceutical products.
• Aluminum comes third at 80 700 ppm. Like silicon, it exists as a compound in the crust.
• Aluminum


  This element is extracted from its compounds commonly through the Bayer and Hall-Heroult processes. It is a lightweight metal used in making utensil foils and packaging materials.
• Aluminum is also used to manufacture automobile parts, rockets, and machinery.
• Iron is extracted from iron ores such as hematite and magnetite
• Iron


  It exists in Earth’s crust with a composition of 50 500 ppm. It has many applications, one of which is for the production of steel.
• Silicon is the primary element used in creating wafers for semiconductors. These semiconductors are used in our electronic devices and gadgets.
• There are two types of crust: oceanic and continental
• Oceanic Crust


  it is composed mostly of dark-colored mafic rocks.
• The density of oceanic crust ranges from 2.9 to 3.1 g/cm3 . The dark color and relatively high density can be attributed to the elevated iron, magnesium, and calcium content of mafic rocks.
• The oceanic crust is thin with thickness varying from 5 to 18 km.
• Oceanic crust hosts feature such as volcanoes and canyons.
• Oceanic Crust


  It can be divided into three regions, namely: continental margins, ocean basins, and ridges.
• Continental margins separate continental crust from oceanic crust.
• Continental margins


  These are prominent between oceanic and continental crust in passive margins. In active margins, the more prominent features are trenches and island arcs
• Deep ocean basins are the areas found between the continental margins and ocean ridges
• Deep ocean basins


  These are the areas where features such as seamounts and abyssal plains can be found.
• Ocean Ridges


  are composed of newly formed oceanic crust which has been uplifted and faulted. These 2 km-high mountain belts occur in the middle of the oceans and wrap around the globe.
• The age of oceanic crust is approximately 180,000 million years old or less
• The second type of crust, the continental crust, is composed of many rock types.
• Continental Crust


  Its major component is granodiorite, a light-colored igneous rock
• The thickness of continental crust reaches up to 80 km in mountainous areas and has an average thickness of 30 km.
• The density of continental crust is lower compared to oceanic crust and may range from 2.6 to 2.9 g/cm3 . It is relatively older than oceanic crust as the rocks along trenches in oceans are continually recycled through the process of subduction