Earth’s atmosphere is a protective blanket, composed of distinct layers. Each layer has unique characteristics, playing a specific role in maintaining conditions for life. These layers regulate temperature, block harmful radiation, and protect Earth from extraterrestrial objects. Understanding these layers provides insight into our planet’s complex dynamics.
Defining the Mesosphere’s Place
The mesosphere is the third major layer of Earth’s atmosphere, above the stratosphere and beneath the thermosphere. This region extends from 50 kilometers (31 miles) to 85 kilometers (53 miles) above Earth’s surface. The lower boundary of the mesosphere is known as the stratopause, marking the transition from the warming trend of the stratosphere. As altitude increases within the mesosphere, temperatures generally decrease, defining its basic structural characteristic.
Earth’s Coldest Atmospheric Layer
The mesosphere is the coldest layer in Earth’s atmosphere. Near its upper boundary, known as the mesopause, temperatures can drop to approximately -90°C (-130°F or 173 K).
This cold is due to very little ozone within this layer to absorb incoming solar ultraviolet radiation. Unlike the stratosphere below, which warms due to ozone absorption, the mesosphere lacks this significant heat source.
The air in the mesosphere is very thin, allowing absorbed heat to radiate efficiently back into space. This combination of minimal solar radiation absorption and effective heat loss contributes to the layer’s cold temperatures. As one ascends through the mesosphere, air density continues to decrease, further aiding this cooling.
Our Meteorite Shield
The mesosphere protects Earth from incoming space debris. Most meteors, often referred to as “shooting stars,” burn up within this atmospheric layer before they can reach the ground.
As these objects enter the atmosphere at high velocities, they encounter sufficient gases in the mesosphere to create friction. This friction generates intense heat, causing the meteors to ignite and disintegrate into small fragments of dust.
While the air in the mesosphere is thin compared to lower layers, it is dense enough to provide the necessary resistance. This function prevents countless objects from impacting Earth’s surface.
The Enigmatic Night-Shining Clouds
Noctilucent clouds (NLCs), also known as polar mesospheric clouds, are a unique phenomenon of the mesosphere. These ethereal, bluish-white clouds are the highest clouds in Earth’s atmosphere, forming at altitudes between 76 and 85 kilometers (47 to 53 miles).
They are typically visible during the summer months at high latitudes, appearing after sunset or before sunrise when the sun’s rays illuminate them from below the horizon.
The formation of noctilucent clouds requires specific conditions. These include the extremely cold temperatures characteristic of the mesosphere, particularly near the mesopause.
A supply of water vapor and tiny dust particles is also necessary for ice crystals to form. These dust particles often originate from micrometeors that have burned up in the mesosphere, providing surfaces for water vapor to freeze.