Arrange the following atmospheric zones in terms of the distance from the earth’s surface in increasing order, and select the correct answer from the code given below: 1) Thermosphere 2) Troposphere 3) Stratosphere 4) Mesosphere Codes:

Option D is correct. Going up from the surface, the order is Troposphere (2), Stratosphere (3), Mesosphere (4), Thermosphere (1).

The core concept is the temperature profile of the atmosphere, which is what defines each layer. The troposphere is the lowest layer, where temperature falls with height and almost all weather occurs. Above it is the stratosphere, where temperature rises with height because the ozone layer absorbs UV radiation. The mesosphere lies above that, where temperature falls again and reaches the coldest point at the mesopause. The thermosphere is the outermost of these four, where temperature rises sharply and the ionosphere sits.

Options A, B and C each put a layer out of place. A puts the stratosphere above the mesosphere, B puts the stratosphere below the troposphere, and C puts the troposphere above the thermosphere.

For Mains (GS-3, environment), the stratosphere matters for ozone depletion and the Montreal Protocol, and the troposphere matters for climate and weather.

Trap: aspirants often memorise the layers in the order of the names rather than in the order of height, and mix up the stratosphere and mesosphere.