Question

Divide the atmosphere into two parts on the basis of its composition. Bring out the difference between the two parts.

Answer 1

The atmosphere can be divided into two parts on the basis of its composition:

1. Homosphere:
   • This is the lower part of the atmosphere up to an altitude of about 80 km from the Earth’s surface.
   • In this layer, the chemical composition of the atmosphere is uniform.
   • Despite the atmosphere thinning with altitude, the blend of gases remains fairly uniform throughout the Homosphere.
2. Heterosphere:
   • This layer begins above 80 km and extends up to around 10,000 km.
   • Above 480 km, the atmosphere becomes extremely rarefied, almost like a vacuum, called the Exosphere or outer space.
   • This region contains very light gases like Hydrogen and Helium, which are loosely held by gravity.
   • The Heterosphere also includes the Thermosphere and the Ionosphere.
   • The Ionosphere contains ions (positively and negatively charged particles) formed by ionization, which helps filter harmful solar radiation and absorbs cosmic rays and gamma rays.

Aspect	Homosphere	Heterosphere
Altitude Range	Surface to 80 km	Above 80 km to 10,000 km
Composition Uniformity	Composition is uniform	Composition is variable (layered by gas type)
Gases Present	Mainly Nitrogen, Oxygen, Argon, and trace gases	Light gases like Hydrogen and Helium dominate at higher altitudes
Atmospheric Density	Relatively denser	Very rarefied, approaching a vacuum
Special Regions	None	Contains the Thermosphere and the Ionosphere
Ionization	Very low ionization	Ionization causes charged particles (ions)
Function	Supports life and weather phenomena	Filters harmful solar radiation and cosmic rays