Earth is the third planet from the Sun and is the largest of the terrestrial planets. The Earth is the only planet in our solar system not to be named after a Greek or Roman deity. The Earth was formed approximately 4.54 billion years ago and is the only known planet to support life.

Structure of the EarthFacts about the Earth
Mass: 5,972,190,000,000,000 billion kg
Equatorial Diameter: 12,756 km
Polar Diameter: 12,714 km
Equatorial Circumference: 40,030 km
Known Moons: 1
Notable Moons: The Moon
Orbit Distance: 149,598,262 km (1 AU)
Orbit Period: 365.26 Earth days
Surface Temperature: -88 to 58°C

Structure of the Earth
The Earth consists of four concentric layers: inner core, outer core, mantle and crust. The crust is made up of tectonic plates, which are in constant motion. Earthquakes and volcanoes are most likely to occur at plate boundaries.
Structure of the Earth

a) Earth’s Crust:
The crust is the outer layer of the earth. It is a thin layer between 0-60 km thick. The crust is the solid rock layer upon which we live. There are two different types of crust: continental crust, which carries land, and oceanic crust, which carries water. These two different types of crust are made up of different types of rock. The boundary between the crust & the mantle is Mohorovicic Discontinuity. All of the Earth’s landforms (mountains, plains, & plateaus) are contained within it, along with the oceans, seas, lakes & rivers.

b) Earth’s Mantle:
It is the thick, dense rocky matter that surrounds the core with a radius of about 2885 km. The mantle covers the majority of the Earth’s volume. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt. This is basically composed of silicate rock rich in iron & magnesium. This layer is separated from the core by Gutenberg-Wiechert Discontinuity. The outer & the inner mantle are separated by another discontinuity named Repetti discontinuity.

c) Earth’s Core:
Earth’s Core is thought to be composed mainly of an iron & nickel alloy. The core is earth’s source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances. The core is divided into two different zones. The outer core is a liquid because the temperatures there are adequate to melt the iron-nickel alloy. However, the inner core is a solid even though its temperature is higher than the outer core. Here, tremendous pressure, produced by the weight of the overlying rocks is strong enough to crowd the atoms tightly together & prevents changing it to the liquid state. The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.

Shape: The shape of Earth approximates an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator.

Tectonic plates: The mechanically rigid outer layer of Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent boundaries, at which two plates come together, divergent boundaries, at which two plates are pulled apart, and transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.

Surface: Earth’s terrain varies greatly from place to place. About 70.8% of the surface is covered by water, with much of the continental shelf below sea level. This equates to 361.132 million km2 (139.43 million sq mi). The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes, oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining 29.2% (148.94 million km sq, or 57.51 million sq mi) not covered by water consists of mountains, deserts, plains, plateaus, and other land forms.

Magnetic field: The main part of the Earth’s magnetic field is generated in the core, the site of a dynamo process that converts kinetic energy of fluid convective motion into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth’s surface, where it is, to rough approximation, a dipole.

Magnetosphere: The extent of Earth’s magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the day-side of the magnetosphere, to about 10 Earth radii, and extends the night side magnetosphere into a long tail. Since the velocity of the solar wind is greater than the speed at which wave propagate through the solar wind, a supersonic bow shock precedes the day-side magnetosphere within the solar wind.