Earth's Atmospheric Composition and Structure

Chemical Composition of the Air

The Earth includes a mix of gases composing the structure of the air. These gases are present in different proportions.

• Nitrogen (N₂): Forms 78% of the air. It is colorless and inert, which means that it does not react chemically with other substances.
• Oxygen (O₂): Forms 21% of the air; it is colorless and indispensable for respiration.
• Other gases: Constitute the remaining 1%:
  • Argon (Ar): Forms 0.9% of the air and is an inert gas.
  • Ozone (O₃): Forms 0.07% of the air. It is very toxic and performs the filter function against the sun's ultraviolet rays, which are harmful to living beings.
  • Carbon dioxide (CO₂): Forms 0.03% of the air, allowing plants to perform photosynthesis; it is also responsible for the greenhouse effect.

The Greenhouse Effect and Its Impact

The Greenhouse Effect: Sunlight reaching the Earth heats the surface. This heat then bounces back but is trapped by the carbon dioxide in the atmosphere, causing the terrestrial temperature to increase.

Consequences of an Increased Greenhouse Effect

Explain the result of an increased greenhouse effect: Why can human activity increase the greenhouse effect?

Human activity increases the greenhouse effect through pollution. If we contaminate the atmosphere, the ozone layer can break. When it breaks, ultraviolet rays fall more easily, which can lead to skin cancer.

Layers of the Atmosphere

The atmosphere is divided into four different layers:

• Ionosphere: Up to 500 km
• Mesosphere: Up to 80 km
• Stratosphere: Up to 40 km
• Troposphere: Up to 10 km

The Ozonosphere and Chemical Reactions

At the top of the atmosphere, there is the ozonosphere. In this particular point in the atmosphere, oxygen reacts with the sun's ultraviolet rays, forming ozone in this way:

O₂ + O₃ = UV

This reaction is exothermic; that is, it produces heat, resulting in a temperature of 17°C.

Evolution of the Primitive Atmosphere

The primitive atmosphere was composed primarily of two gases: carbon dioxide and water vapor. As water vapor condensed, it formed a series of precipitations that created the Earth's hydrosphere (the formation of oceans, rivers, and lakes).

Atmospheric Layer Altitudes

• Ionosphere: 500 km
• Mesosphere: 80 km
• Stratosphere: 40 km
• Troposphere: 10 km

Comparison of Primitive and Current Atmospheres

The Primitive Atmosphere

• Water Vapor (H₂O): Led to rain.
• CO₂ (95%): Led to photosynthesis and the formation of limestones.
• Oxides: Dissolution processes (O5 -> plasters; ON -> O.2).
• Argon and Nitrogen: Present in trace amounts.

The Current Atmosphere

• Oxygen (O₂) 21%: Result of photosynthesis.
• Ozone (O₃): Formed from O₂.
• Carbon Dioxide (CO₂) and Argon: Approximately 1%.
• Nitrogen: 78%.