Understanding the Ozone Layer and Its Vital Role
The Ozone Layer: A Vital Shield
The ozone layer is a region of the stratosphere containing a relatively high concentration of ozone. This layer, extending approximately 15 km to 40 km in altitude, contains 90% of the ozone in the atmosphere and absorbs 97% to 99% of high-frequency ultraviolet radiation.
Formation of the Ozone Layer
Our planet, due to its size and average mass, was unable to retain light gases such as hydrogen and helium, which escaped, swept away by the solar wind. Once the solar wind slowed, the terrestrial planets rebuilt their atmospheres (those that could). The Earth, from its abundant gases expelled from volcanoes, successfully created a discreet atmosphere consisting of carbon dioxide, nitrogen, water vapor, and sulfur, with traces of other elements. It should be noted that CO2 was likely more abundant in that early atmosphere than it is at present. We know that the sun, at that time, emitted less energy than today (about 30% less). As the sun entered the helium phase, becoming more stable and energetic, the CO2, the main greenhouse gas, offset the initial lack of heating, allowing for warm temperatures at the surface and the liquefaction of water.
Location of the Ozone Layer
The ozone layer is a region of the atmosphere located between 19 and 48 km above the Earth’s surface.
How Ozone is Formed
Ozone concentrations reach up to 10 parts per million (ppm) within the ozone layer. At ground level, such high concentrations are hazardous to health. Ozone is a form of oxygen whose molecule has three atoms instead of the two found in common oxygen. The third atom makes it poisonous; even a small amount of this substance inhaled for a short period can be deadly. Ozone is an unstable gas and can be destroyed by natural compounds containing nitrogen, chlorine, and hydrogen. The ozone layer protects life on Earth from short-wave ultraviolet radiation (UVC). UVA, the longest wavelength, is relatively harmless and passes almost entirely through the layer. Between the two is UVB, which is less lethal than UVC but still dangerous; the ozone layer absorbs most of it. Obviously, there can be no doubt about the importance of the ozone layer.
How Ozone Decomposes
The Sun’s ultraviolet radiation decomposes oxygen molecules into single atoms, which then combine with other oxygen molecules to form ozone. Natural nitrogen compounds in the atmosphere seem to be responsible for maintaining the ozone concentration at a reasonably stable level.
Ozone decomposes through the action of chlorofluorocarbons or CFCs (compounds of fluorine, a poisonous, gaseous halogen substance). Chlorine, a secondary compound of CFCs, attacks ozone, which consists of three oxygen atoms, by snatching one away and forming chlorine monoxide. This chlorine monoxide then reacts with oxygen atoms to form oxygen molecules, releasing chlorine, which continues to decompose ozone molecules.
Importance in the Evolutionary Process
Ozone is a gas composed of three oxygen atoms (O3), and its importance for the survival of living beings is paramount. The ozone layer acts as a filter, or shield, against harmful, high-energy radiation reaching the Earth, allowing other types of radiation, such as ultraviolet, to pass. This ultraviolet radiation is essential for life on the planet as it enables photosynthesis in plants, which form the base of the trophic pyramid.