The Atmosphere: the Vital Gaseous Envelope of the Earth

How is the atmosphere constructed?

The atmosphere is the gaseous envelope that surrounds the planet earth. It is retained by gravity and extends to a height of about 1000 km. The atmosphere consists of several layers, which are separated by so-called 'pauses'. The atmospheric pressure decreases with increasing height and at some point the air becomes too thin for breathing. Temperatures show a varying pattern.

The lowest stratum is the troposphere. That’s where we live and where the weather takes place. With increasing height, the temperature drops down to -50 °C.

In the stratosphere, which is above the troposphere, the temperature rises again. The ozone layer, which blocks off dangerous ultraviolet irradiation, is situated here.

The next layer is the cold mesosphere..

In the thermosphere, in contrast, temperatures up to 2000 °C prevail, due to solar irradiation.

The highest layer is the exosphere, which gradually turns into the vacuum of space.

How was the present atmosphere formed?

The composition of the atmosphere has changed a lot over the course of evolution. In the earliest times, the atmosphere was composed of methane, ammonia, hydrogen, carbon dioxide and hydrogen sulphide. Oxygen was only set free when aquatic bacteria and algae developed photosynthesis, three thousand million years ago. At first, the oxygen endangered the existing life at the time. It could only adapt to the new environment because of the 'invention' of respiration.

As soon as oxygen was enriched in the atmosphere, the ozone layer was able to form and offer protection from the UV irradiation of the sun. This was the only thing that enabled the colonisation of land.

The American chemist Stanley Miller made an experiment about the origin of life. He simulated lightning in the initial atmosphere by exposing a mixture of water, hydrogen, methane and ammonia to an electric discharge. Would you believe it, after a few days organic molecules had formed!

What significance does the atmosphere have for us?

Life would not be possible without the atmosphere and would not have developed at all as it is known on earth today. We use the vital oxygen of the air, and the ozone layer protects us from hostile sun irradiation.

Furthermore, the atmosphere creates beautiful daily phenomena: the blue of the sky and the colours of sun set and sun rise. The sunlight is scattered on air molecules, meaning that it is refracted in all directions and lessened in its intensity. Short-waved blue light is scattered more intensely than red light, therefore the sky looks blue during the day. When the sun sets or rises, it is further away from us and the light has to cover a longer distance through the atmosphere. As a result, the blue part is more attenuated and the sky on the horizon appears yellow and the sun red.