CBSE Questions for Class 7 Geography Inside Our Earth Quiz 1 - MCQExams.com

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.

• Rock cycle is the transition of rocks of 3 basic types viz igneous, sedimentary and metamorphic into each other in a cyclic manner.
  
• Primary rock is an igneous rock which is formed after solidification of lava. It may then get eroded and settled as various layers to form sedimentary rocks. The sedimentary rocks get metamorphosised under high pressure and temperature beneath the earth crust which forms metamorphic rocks.
• Finally, all types of rocks may get subducted deep inside the earth were under extreme temperatures they get melted leading to the formation of liquid magma and the cycle repeats.
• Thus all options are part of this cycle and option D is correct.

• 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.

• 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

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

Mantle is the widest of all the layers, which is 1800 miles thick. It is composed mostly of silicate rocks rich in magnesium and iron. It is found beneath the earth’s crust. The temperature of this layer is 1600 degrees Fahrenheit at the top to about 4000 degrees Fahrenheit near the bottom.