Inside our Earth Test - 6

Basically there are three main types of rocks found in nature that are sedimentary, metamorphic and igneous. Sedimentary are formed from particles of sand, shells, pebbles and other fragments of material. Metamorphic are formed under the earth's surface by metamorphosis and igneous are formed when magma cools and hardens.

The three main layers of Earth include the crust (1 percent of Earth's volume), the mantle (84 percent), and the core (inner and outer combined, 15 percent). The outermost of all these three is the crust. 

• Marble is formed when limestone is subjected to intense heat and pressure leading to its metamorphism i.e. change in form. Hence marble is called a metamorphic rock

• The average thickness of earth crust at ocean floors- 8 km 
• The average thickness of earth crust at continents- 32 km
• Thus the earth crust is thicker at continents as compared to oceans floors.

Earth mainly consists of four layers namely crust, mantle, outer core and inner core:

Crust: This is about 8 km thick inside and is highly explored. The continental crust is composed mostly of granite. The oceanic crust consists of a volcanic lava rock called basalt.

Mantle: It is the largest layer of the Earth which is 1800 miles thick. It is composed mostly of silicate rocks rich in magnesium and iron.

Outer core: It is located beneath the mantle. The outer core is composed of melted metals like nickel and iron.

Inner core: It is composed of an iron-nickel alloy and some light elements.

Layer that lies immediately after the mantle is the outer core.

Sial refers to the earth’s crusts upper layer, it is made up of rocks abundant in silicate and aluminium-based minerals. The word Sial itself is an amalgam of the first two letters of aluminium and silica, Sial runs anywhere from 5-70KM deep from the surface.

Mental is the middle layer of the earth lies between crust and core. The average thickness of this layer is 100 to 2900 km. Silica and magnesium elements predominate in this layer so it is known as SIMA.  Density of the layer varies between 3.1 to 5.00. It has two layers: upper mantle and lower mantle.  

Igneous rocks are formed during the formation of the upper crust of the earth on cooling, solidification, and crystallization of hot and liquid magmas after the origin of the earth. Igneous rocks are mostly associated with the volcanic activities and igneous rocks are generally found in the volcanic zones.

Igneous rocks begin the rock cycle, and are therefore called primary rocks. Two major divisions include- volcanic or extrusive rocks that form when magma is ejected from the Earth's crust, and intrusive rocks, which are created below the surface.

Sima is the name for the lower layer of the Earth's crust. This layer is made of rocks rich in magnesium silicate minerals. Typically when the sima comes to the surface it is basalt, so sometimes this layer is called the 'basalt layer' of the crust. The sima layer is also called the basal crust or basal layer because it is the lowest layer of the crust. Because the ocean floors are mainly sima, it is also sometimes called the oceanic crust.