The atmosphere is a layer of gasses, held in by gravity, that surround the planet. The atmosphere has a vital role in protecting life by: absorbing harmful ultraviolet radiation, warming the surface of the planet and reducing temperature extremes between the night and day. Many of the gasses contained in Earth’s atmosphere, known as air, are also essential for life. The content and pressure of air changes at different heights and the atmosphere becomes thinner as altitude increases. By studying the atmosphere it was discovered that there are a number of atmospheric layers with different properties such as: temperature, air pressure and density.
What are the layers of Earth’s atmosphere?
Depending on the definition the atmosphere is divided into four or five main layers.
The first layer is known as the troposphere, which extends from the surface of the Earth to somewhere between 9 km (30,000 ft) to 17km (56,000 ft) depending on the location. This layer makes up about 80% of the entire mass of the atmosphere.
The second layer is called the stratosphere, which extends from the tropopause (boundary between the troposphere and stratosphere) to somewhere between 50 -55 km (160,000 – 180,000 ft).
The third layer is called the mesosphere, which extends from the stratopause to 80-85 km (260,000 – 280,000 ft). This is the coldest atmospheric layer and the boundary of the mesosphere, known as the mesopause, can reach -100 °C (?150 °F)!
The fourth layer is known as the thermosphere, which begins at the mesopause and extends to 350-800 km (1,100,000–2,600,000 ft) depending on solar activity. The temperature of this layer can reach 1,500 °C (2,700 °F)!
The exosphere is the final atmospheric layer and reaches from the exobase (top of the thermosphere and base of the exosphere) and extends at least 100,000 km (62,000 mi) into space. The particles of gas in the exosphere, mostly hydrogen and helium, are so far apart that they rarely collide with another particle! There is no clear boundary between this layer of atmosphere and space, which means that it is sometimes actually considered to be a part of outer space.