Interior of the Earth

• The crust is the uppermost layer of the Earth. It is the thinnest of the three layers, forming just about 1% of the Earth's volume. The crust varies in thickness from just around 5-10 km under the oceans, to around 35-70 km under the continents.
• The crust


  • The upper crust makes up the continents. It mainly consists of the minerals silica and aluminium, and is therefore also called Sial.
  • The lower crust is a continuous layer of denser rock that includes the ocean floor. It is made of the minerals silica, iron and magnesium, and is therefore called Sima.
• The mantle


  • The upper mantle is a thin, stiff layer consisting mainly of the minerals silica, iron and magnesium. It extends from the bottom of the crust to a depth of around 300 km.
  • The lower mantle extends from where the upper mantle ends to around 2900 km. It is a zone of mixed minerals such as iron, magnesium, aluminium and silicon. The average temperatures here are 3000 °C. As a result of the high temperature and pressure, the lower mantle is semi-solid, and materials here can move slowly in a plastic manner.
• The core


  • The outer core is about 2300 km thick and the inner core is around 1200 km thick.
  • The outer core is so hot that it is molten (liquid core); the inner core, though hotter, is under such extreme pressure that it remains solid (solid core).
  • The temperature in the inner core is hotter than that on the Sun's surface. The intense heat from the inner core causes material in the outer core and the inner mantle to move around.
• Lithosphere


  The topmost layer of the Earth, made up of the crust and the top part of the upper mantle. It is rigid and brittle.
• Asthenosphere


  The semi-solid layer of the upper mantle. It is ductile (capable of being bent) in nature.
• The lithosphere floats on the asthenosphere
• Igneous rocks


  • The hot lava that flows out during volcanic eruptions cools down, solidifies over a period of time and forms igneous rocks.
  • Primary rocks formed on the surface of the Earth are called extrusive rocks. They have a fine-grained structure.
  • Magma (molten rock) that gets trapped in veins deep inside the Earth cools down over a long period of time and forms intrusive rocks.
• Igneous rocks


  • Basalt
  • Granite
• Sedimentary rocks


  • Over a period of several thousand years, sediments carried by agents of gradation (like water, ice, and the sea), are deposited in layers over the Earth. The sediments may consist of weathered and fragmented rock materials, micro-organisms, and plant and animal remains.
  • As the deposition of sediments builds up, the pressure exerted by the upper layers squeezes the sediments into layered rocks called sedimentary rocks.
• Sedimentary rocks


  • Shale
  • Sandstone
  • Conglomerate
• Over millions of years, organic matter, such as the remains of plants and animals, trapped between the sedimentary layers, gets converted into fossil fuels, namely, coal, petroleum and natural gas. Fossils and fossil fuels usually form in sedimentary rocks.
• Metamorphic rocks


  • When rocks are subjected to conditions of intense heat and pressure, many of them metamorphose, or change completely, into new kinds of rocks. Such rocks are called metamorphic rocks. Here, the parent rock undergoes a chemical change.
• Metamorphic rocks


  • Marble
  • Quartzite
  • Schist
  • Gneiss
  • Slate
• The rock cycle


  1. Igneous rocks are made by the cooling and solidification of molten magma. They are thus considered to be the primary rocks or parent rocks of the crust.

  2. When rocks are subjected to weathering and erosion, sediments are formed, and get deposited in layers. These layers get compacted and cemented over time and become sedimentary rocks.

  3. When sedimentary and igneous rocks are exposed to tremendous heat and pressure, they change to become metamorphic rocks.

  4. Under extreme heat, all rocks melt to become magma. The magma comes to the surface of the Earth, cools and forms igneous rocks. And the rock cycle starts once more.
• Minerals


  Rocks are composed of different naturally occurring substances called minerals. Minerals are solid and inorganic. Each mineral has a unique chemical composition.
• Igneous rocks


  Made by the cooling and solidification of molten magma, considered the primary or parent rocks of the crust
• Formation of sedimentary rocks

  Weathering and erosion form sediments, which get deposited in layers, compacted and cemented over time
• Formation of metamorphic rocks

  Sedimentary and igneous rocks exposed to tremendous heat and pressure change to become metamorphic rocks
• Rock cycle


  Rocks transform from one type to another in a continuous cycle: Igneous -> Sedimentary -> Metamorphic -> Igneous
• Minerals


  Solid, naturally-occurring inorganic substances that make up rocks
• Types of minerals


  • Metallic
  • Non-metallic
• Metallic minerals


  Minerals that contain one or more metallic elements, usually hard with shiny surfaces, can be hammered into thin sheets or stretched into wires, and are good conductors of heat and electricity
• Non-metallic minerals


  Minerals that do not contain extractable metallic elements, lack a metallic shine, are poor conductors of heat and electricity, and cannot be stretched into thin wires
• Metallic minerals


  • Iron
  • Copper
  • Bauxite
  • Gold
  • Manganese
• Non-metallic minerals


  • Limestone
  • Mica
  • Gypsum
• Uses of rocks and minerals

  • Provide nutrients in soil for plants
  • Used for construction work
  • Used in industries (ores)
  • Used in making jewellery (precious metals and gemstones)
• Fossil: The remains or impressions of ancient organisms (plants or animals) that have been preserved by natural processes
• Sial


  The upper crust, made mostly of silica and aluminium
• Sima


  The lower crust, consists largely of silicates and magnesium minerals
• Nife


  The core, made up largely of nickel and iron
• Plastic


  (When referring to semi-solid materials) Capable of moving slowly
• Magma


  The molten rock material in the lower mantle
• Lava


  Magma released onto the surface of the Earth
• Weathering


  The breaking up and fragmentation of rock material exposed to agents of gradation like wind, water and ice
• Gradation


  The continuous process of levelling of the Earth's surface
• Fossil fuels


  Fossils that have been converted to sources of energy, such as petroleum, coal and natural gas
• Organic


  Relating to or obtained from non-living matter
• Inorganic


  Relating to or obtained from non-living matter
• After the death of Harshavardhana in 647 CE, his empire broke up into several small states and kingdoms, each ruled by a different dynasty or a clan (social group)