Earth's Atmosphere Composition and Phenomena

Understanding Earth's Atmosphere

Atmospheric Composition Evolution

Primitive Atmosphere: Composed of water vapor, carbon dioxide, nitrogen, hydrogen, ammonia, methane, and other oxides, but notably *no oxygen*.

Present Atmosphere: Consists of approximately 78% nitrogen, 21% oxygen, 1% carbon dioxide, water vapor, and trace gases like argon. The ozone layer later formed from oxygen.

Atmospheric Layers (In Order)

• Ionosphere: Temperature around 1,000 ºC.
• Mesosphere: Approximately 40 km thick.
• Stratosphere: Approximately 30 km thick. Temperature increases from 0 ºC at its upper limit to 70 ºC at its lower limit (Note: The original text stated an increase *to* 0ºC, which is inconsistent with standard models; this reflects the general structure).
• Troposphere: Contains 80% of the atmosphere's total mass.

Key Atmospheric Phenomena

Global Warming

In the last century, our atmosphere has warmed between 0.5 and 0.9 ºC on average. Some scientists suggest that air pollution is causing the Earth's surface to heat up.

Acid Rain

Rain is naturally slightly acidic due to dissolved carbon dioxide. Pollutants such as sulfur dioxide and nitrogen oxides react with water to form acids when mixed with rain.

The Hole in the Ozone Layer (O3)

Ozone is present throughout the atmosphere, primarily concentrated in the stratosphere. Ozone is being destroyed by air pollution. Chemicals called chlorofluorocarbons (CFCs), used in aerosols and refrigerators, escape into the atmosphere. They react with the ozone and destroy it, allowing harmful solar radiation to enter through this thinning area.

What Is the Greenhouse Effect?

The greenhouse effect is a natural phenomenon. The atmosphere absorbs a significant amount of solar radiation. CO2 in the atmosphere acts like the glass walls of a greenhouse; it traps heat and prevents it from returning immediately to space. This process keeps the Earth warm. Without an atmosphere, our planet would be much colder.

The Water Cycle

• Evaporation: Liquid water changes to a gas (water vapor). Water moves from the hydrosphere to the atmosphere.
• Evapotranspiration: Water evaporates into the atmosphere from the leaves and stems of plants.
• Condensation: Water vapor changes back to liquid, forming clouds and dew.
• Precipitation: Water in clouds falls to the ground as rain, snow, or hail.
• Surface Runoff: Surface water moves across the land, forming rivers and streams.
• Infiltration: Surface water filters into the ground. This occurs more easily if the ground is porous.

Water Pollution Example

Exercise 5: Water is polluted because people discard items such as plastic bags, drink cans ("latas"), etc. Furthermore, when boats sink at sea, they release very contaminated substances such as oil.