Question

The outermost layer of earth’s atmosphere is
A. stratosphere
B. mesosphere
C. troposphere
D. ionosphere

Answer 1

Hint: Atmosphere is a set of layers of gases that are surrounding a planet which is held by gravity. The Earth’s atmosphere is classified into layers or spheres. It is based on the different gradients of temperature and the function of altitude.

Complete step-by-step answer:
Troposphere: The troposphere is between 0 to 15 kilometers from Earth’s surface. It is the first layer above Earth’s surface and consists of about 80 to 90% of mass of the Earth’s atmosphere. It is based on the decreasing of temperature with increasing altitude. It is most probably the result of heating of Earth’s surface due to the incoming solar radiation. The heat is transferred to the troposphere and the weather occurs in this layer.

Stratosphere: The stratosphere layer is approximately between 15 to 50 kilometers from Earth’s surface. It is based on the temperature rise due to increasing height. The warming may be the result of absorption of solar radiation by ozone layer, which helps to prevent the harmful ultraviolet radiations from sun reaching the Earth’s surface.

Mesosphere: The mesosphere is between 50 to 90 kilometers from Earth’s surface. It is based on the decrease in temperature with further increase in altitude which goes about -90℃. Most of the meteors entering the Earth’s atmosphere get burned in this layer.

Thermosphere: After those three layers, the thermosphere takes over where temperatures increase with altitude. This layer’s atmosphere is first exposed to the sun's radiation. It also includes a region called the ionosphere where the atmosphere is filled with charged particles.
Therefore, the correct answer for the given question is option (D).

Note: The upper limit of Earth’s atmosphere is called the exosphere where the atmosphere gets merged with outer space. It is very thin and almost air less, the molecular densities are low and has low chance of collision between the molecules.