# Write a note on Earth.

ANS:


* Considering the distance from sun, earth is the third planet of our solar system.
* It is the only planet of our solar system where life exists because it has a thin layer of atmosphere which extends up to about 800 to 1000 km.
* Atmosphere protects us from meteors as they burn out due to friction before reaching the earth's surface.
* The ozone layer of atmosphere blocks ultraviolet rays of solar radiation from reaching the surface and protects us from its harmful effects.
* The natural Green House Effect due to gases like carbon dioxide and methane keeps the atmosphere warm enough to sustain life.
* Due to all these favourable circumstances life originated and sustained on the earth.
* The surface of the earth is solid (rocky) and has very large proportion of silicon dioxide.
* The core region is made up of molten (semiliquid) mass containing iron, magnesium, silicates, etc.
* It has one natural satellite (moon).