The Atmosphere
Earth is wrapped in layers of mixed gases, and as a group they are called the atmosphere. The atmosphere has 5 layers, which are as follows:
- troposphere (0 - 6/20km above Earth)
- stratosphere (6/20 - 50/60km above Earth)
- mesosphere (50/60 - 85/120km above Earth)
- thermosphere (85/120 - approx. 600km above Earth)
- exosphere (over 600km above Earth)
- Troposphere
The troposphere is the lowest layer of the atmosphere, containing 75% of the atmosphere's mass. The troposphere extends higher at the equator (where it can extend up to 10 km high) than at the poles (where it only extends around 5km high). The troposphere contains 99% of the atmosphere's water vapour, and the water cycle occurs in this layer of the atmopshere. Water vapour concentrations vary throughout the troposphere, with the highest concentration above the tropics (3-4%) which decreases further north and south to eventual trace amounts around the poles. Weather is also something that occurs solely in the troposphere, affecting the inhabitants of the lands below.
The air here is made up of 78% nitrogen gas, 21% oxygen gas, 1% trace gases such as argon, carbon dioxide, and trace amounts of helium, hydrogen, and ozone. Carbon dioxide is observed in small amounts but its presence has doubled since 1900. Ozone in the lower troposphere does not have any positive effect, with UV rays reacting with pollution to create toxic chemicals and ozone gas (together called smog).
The sun warms the air at the equator more than at the poles. This uneven heating of the regions of the troposphere causes convection currents. Convection currents are large scale patterns of winds that move heat and moisture around the globe.
The air here is made up of 78% nitrogen gas, 21% oxygen gas, 1% trace gases such as argon, carbon dioxide, and trace amounts of helium, hydrogen, and ozone. Carbon dioxide is observed in small amounts but its presence has doubled since 1900. Ozone in the lower troposphere does not have any positive effect, with UV rays reacting with pollution to create toxic chemicals and ozone gas (together called smog).
The sun warms the air at the equator more than at the poles. This uneven heating of the regions of the troposphere causes convection currents. Convection currents are large scale patterns of winds that move heat and moisture around the globe.
Stratosphere
The stratosphere is the second layer of atmosphere, separated by the troposphere by the tropopause. The ozone layer (a concentration of ozone that helps shield Earth from harmful levels of UV radiation from the Sun) exists in this layer of the atmosphere. The radiation itself created the ozone layer; radiation causes the molecular oxygen (O2) molecules to separate, which then individually recombines with other atomic oxygen (O) particles to create ozone(O3).
Because of the ozone layer, the temperature is converse to that of the troposphere, with the temperatures being warmer in the higher layers and cooler in the lower layers. The upper layers of stratosphere is where ozone layer is located. Ozone absorbs some energy from the Sun and reacts with it to become atomic oxygen and molecular oxygen. Middle layers of the stratosphere have less exposure to UV radiation, which allows O and O2 to combine to create ozone. Lower layers of stratosphere are exposed to minimal amounts of UV radiation, so there is barely any atomic oxygen or natural ozone to be found. Fun fact - airplanes fly here because the stratosphere is stable, above weather, and atmospheric convection does not occur here. |
Mesosphere
The mesosphere is the third and middle layer in the atmosphere, separated from the stratosphere by the stratopause. The exact boundaries of mesosphere vary with seasons and location, and temperature decreases as altitude increases in this layer. In fact, the top of mesosphere is the coldest place in Earth's atmosphere, reaching temperatures of -90 degrees Celsius.
The mesosphere itself is not well researched compared to other layers, due to how difficult it is to study this particular layer. Weather balloons and jet planes cannot fly to this level, and satellites are found in the thermosphere (the layer above). This means it is hard to get instruments up there to receive data from this layer. The only thing that can retrieve data is sounding rockets, which go up into the area of the mesosphere but don't go into orbit.
Fun fact - most meteors we see burn or vaporize completely in this layer due to collisions with the gas particles. High concentration of iron and metal atoms can be found in this layer due to meteors.
The mesosphere itself is not well researched compared to other layers, due to how difficult it is to study this particular layer. Weather balloons and jet planes cannot fly to this level, and satellites are found in the thermosphere (the layer above). This means it is hard to get instruments up there to receive data from this layer. The only thing that can retrieve data is sounding rockets, which go up into the area of the mesosphere but don't go into orbit.
Fun fact - most meteors we see burn or vaporize completely in this layer due to collisions with the gas particles. High concentration of iron and metal atoms can be found in this layer due to meteors.
Thermosphere
The thermosphere is the largest layer in the atmosphere, separated from the mesosphere by the mesopause. Temperatures climb as altitude increases in the thermosphere due to absorption of solar radiation.
Concentrations of different gases vary as altitude increases in thermosphere. Molecular nitrogen and oxygen are abundant in the lower layers of the thermosphere, whereas atomic nitrogen and oxygen as well as hydrogen and helium are found towards the top of the thermosphere. Many satellites orbit here, as well as the International Space Station. Another fun fact - aurora occurs here due to collisions between charged particles and particles in the atmosphere (the particles are excited to higher energy states and get rid of the excess energy as photons, which is seen as the aurora). |
Exosphere
The exosphere is the highest layer of the atmosphere, separated from the thermosphere by the thermopause/exobase. It is the highest level on Earth where particles are gravitationally bound to Earth, and is considered a transitional zone between the atmosphere and interplanetary space.
Gases prevalent here are the lightest atmospheric gases, predominately hydrogen with some helium, carbon dioxide and atmoic oxygen found in the lower exosphere.
Gases prevalent here are the lightest atmospheric gases, predominately hydrogen with some helium, carbon dioxide and atmoic oxygen found in the lower exosphere.
Role of the Atmosphere in Earth's Climate System
The atmosphere reflects a large percentage of the solar radiation that comes towards Earth, protecting it from harmful UV radiation. It also reflects some light reflected off Earth back to Earth, heating the planet to temperatures where living things can thrive. The above energy exchanges keep average temperatures on Earth from changing drastically from year to year.