ATMOSPHERE: Origin, Composition and Structure, Atmospheric particles, Oxygen Consumers, Aerosols, Troposphere, Stratosphere, and Thermosphere

ATMOSPHERE: Origin, Composition and Structure, Atmospheric particles, Oxygen Consumers, Aerosols, Troposphere, Stratosphere, and Thermosphere


A band of gases encircling the Earth’s surface is one of the four elements of the ecosystem (the other three being the biosphere, hydrosphere, and lithosphere). Within 20 miles of the surface of the earth, 99 percent of its mass is concentrated. The atmosphere just disappears into space, having no outer bound.

Compared to the Earth of today, the early Earth would have been extremely different and hostile. Primordial heat, which results from the decay of short-lived radioactive elements, was the reason it was extremely hot.

Consequences – Continuous volcanic activity, a surface that is too hot for liquid water to exist on it or for life as we know it, a molten surface, or a thin, unstable layer of basaltic crust. The makeup of the early atmosphere was most likely entirely different (H2, He). After that, there was a cooling process, primordial heat was released into space, precipitation condensed, and surface water accumulated.  formation of a new atmosphere as a result of volcanic emissions  Environments suitable for the evolution of life

Evolution of the Atmosphere 

Today’s Chemical Composition: 78% nitrogen (N2), 21% oxygen (O2), 0.03% carbon dioxide (CO2), and a few additional gases (such as H2O).

First Atmosphere 

Composition: most likely H2, He

Earth’s gravity is not strong enough to contain lighter gases, which is why these gases are very rare on Earth compared to other places in the cosmos. They were most likely lost to space early in Earth’s history. o The Earth’s magnetic field (magnetosphere = Van Allen Belt), which deflects solar winds, was still not produced by a differentiated core (solid inner/liquid outer core).  The heavier gasses might be held once the core is separated.

Second Atmosphere

Produced through the release of volcanic gas.

The gases generated (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) NH3 (ammonia) and CH4 (methane) were most likely identical to those produced by contemporary volcanoes. 

Not present in volcanic gasses, hence is no free O2 at this moment.

Ocean Formation: In the Early Archean, H2O created by outgassing could exist as a liquid due to Earth’s cooling. This allowed for the formation of oceans.

Oxygen Addition to the Atmosphere

Currently, there is about 21% free oxygen in the sky. How did the atmosphere’s levels of oxygen get to this point?

Oxygen Production

Photochemical dissociation – Water molecules split apart by UV-produced O2 levels, a process known as photochemical dissociation. 1-2% current levels At these levels O3 (Ozone) can form to shield Earth’s surface from UV Photosynthesis – CO2 + H2O + sunlight = organic compounds + O2 – produced by cyanobacteria, and eventually higher plants – supplied the rest of O2 to the atmosphere. 

Oxygen Consumers

Chemical weathering occurs when surface materials (early consumers) oxidize. After a long time, animal respiration, Fossil fuel combustion (much, much later)


Nitrogen and oxygen make up 99 percent of the atmosphere. Water vapour, carbon dioxide, argon, and other trace gases make up the final 1%. These two gases are referred to be permanent gases in the atmosphere because their concentrations in the atmosphere have remained relatively stable in recent years. Compared to nitrogen and oxygen concentrations, the concentrations of certain atmospheric gases change throughout time. We refer to them as variable gasses. Certain gases, like ozone and water vapour, can differ greatly from location to location. The quantity of energy that the atmosphere receives and returns to the Earth’s surface is largely controlled by the concentrations of some of these gases, such as carbon dioxide and water vapour.

Atmospheric particles

A variety of solid particles, including ice, salt, and dust, are also present at varying levels in the Earth’s atmosphere. Wind carries dirt and dust particles that are too small for the atmosphere to contain. Moreover, salt from seawater spray is picked up by winds. In the atmosphere, small dust particles can also harbour airborne microbes like bacteria and fungi.

 Aerosols: Aerosols are tiny solid and liquid droplets that are suspended in the atmosphere. They act as cloud formation’s condensation nuclei.

Air Pollutant: Air pollutants are gases or aerosols created by human activities that pose harm to the environment or living things due to their concentration.


the layer nearest to Earth’s surface holds the majority of the atmosphere’s mass. In the troposphere, weather happens. As one ascends higher into the troposphere, the air temperature drops. The tropopause is the altitude at which the temperature stops falling. The tropopause is located between 16 km and 9 km above the Earth’s surface, respectively, between the tropics and the poles. The tropopause can experience temperatures as low as -60°C.


The stratosphere, which contains the ozone layer and is located above the tropopause, is a layer in which air temperature mostly rises with height. The temperature in the lower stratosphere, which is located beneath the ozone layer, is constant with height. On the other hand, as altitude rises, the temperature in the stratosphere rises, beginning at the bottom of the ozone layer. Ozone molecules, which absorb UV rays from the Sun, are to blame for this warmth. The air temperature ceases to rise with height at the stratopause. Approximately 48 kilometres above the Earth’s surface is the stratopause. 99.9% of the Earth’s atmosphere is found below the stratopause.


The mesosphere, located between 50 and 100 kilometres above the Earth’s surface, is located above the stratopause. The temperature of the air in the mesosphere drops with height. This layer absorbs extremely little solar light, which causes the temperature to drop. The mesopause is the point at the top of the mesosphere where temperature decreases with altitude. 


Between roughly 100 and 500 kilometres above Earth’s surface is the thermosphere. This layer can reach temperatures of a thousand degrees Celsius. Large amounts of solar energy are absorbed by the thermosphere. Heat is produced when it absorbs ultraviolet and x-ray radiation from the sun. Included in the thermosphere is the ionosphere, a cloud of electrically charged particles. 


The outermost layer of Earth’s atmosphere is known as the exosphere. The exosphere is located between 500 and 10,000 kilometres above the surface of the Earth. At the summit of the exosphere, there is no distinct barrier. Rather, the exosphere might be conceptualized as the area that lies between Earth’s atmosphere and space. As altitude rises, the number of atoms and molecules in the exosphere decreases dramatically. Atoms and molecules are so far apart in the exosphere that collisions between them are rare.

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