Study Notes for Topic 4.4 Earth’s Atmosphere

TOPIC 4.4 Earth's Atmosphere

Essential Knowledge

• ERT-4.D.1: The atmosphere consists of major gases, each with a unique relative abundance.

• ERT-4.D.2: The layers of the atmosphere are distinguished by temperature gradients and include:

  • Troposphere

  • Stratosphere

  • Mesosphere

  • Thermosphere

  • Exosphere

Suggested Skill

• Visual Representations 2.A: Describe characteristics of an environmental concept, process, or model presented visually.

Major Gases and Their Relative Abundance

• Earth's atmosphere is predominantly composed of the following gases:

  • Nitrogen (N2)

  • Oxygen (O2)

  • Trace amounts of:

    • Carbon Dioxide (CO2)

    • Argon (Ar)

    • Water Vapor (H2O)

    • Other trace gases.

Historical Changes in Atmospheric Composition

• Throughout Earth's history, the composition of the atmosphere has changed significantly:

  • Early atmosphere was primarily composed of carbon dioxide (CO2), nitrogen (N2), carbon monoxide (CO), and hydrogen gas (H2).

  • Approximately 2.7 billion years ago, the presence of microbial life that conducted photosynthesis led to an accumulation of oxygen.

  • Currently, human activities are modifying the concentrations of various atmospheric gases, especially:

    • Carbon Dioxide (CO2)

    • Methane (CH4)

    • Ozone (O3).

Layers of the Atmosphere

Overview

• The atmosphere is categorized into distinct layers based on temperature gradients. Follow the mnemonic device “Strawberry Milkshakes, They’re Excellent” for an easy recall of layers.

Troposphere

• Characteristics:

  • Contains most of Earth's weather.

  • Home to clouds, and conventional aviation.

  • A significant amount of circulation and mixing of gases occurs here.

  • Mass: Holds approximately ¾ of the atmosphere's mass despite being thin due to gravitational pulling making air denser closer to Earth's surface.

  • Temperature: Air temperature decreases with altitude.

  • Note: This layer is closest to Earth's surface.

Stratosphere

• Characteristics:

  • Altitude Range: Extends from 7 to 31 miles above sea level.

  • Composition is similar to the troposphere but is much drier and less dense.

  • Minimal vertical mixing of gases, leading to long residence times for substances.

  • Temperature Variation: Increases with altitude due to ozone and oxygen absorbing UV radiation.

  • Ozone Layer: A specific region within this layer known as the ozone layer that absorbs and scatters incoming UV radiation, protecting Earth's surface from harm. This layer is referred to as “Good Ozone”.

Mesosphere

• Characteristics:

  • Temperature: Decreases with altitude due to reduced density of air molecules absorbing sunlight, making it the coldest atmospheric layer.

  • Function: Incoming meteors burn up in this layer.

Thermosphere

• Characteristics:

  • Host to the Northern Lights, known as the Aurora Borealis.

  • Temperature: Highest temperatures found in this layer as it absorbs highly energetic solar radiation.

Exosphere

• Characteristics:

  • Outermost layer of Earth's atmosphere.

  • Composed of extremely thin air with gas molecules so sparse that they rarely collide.

  • This layer represents a gradual transition into outer space and does not have a defined upper boundary.

  • The boundary at the bottom is referred to as the thermopause, where most satellites orbit.

Temperature Gradients and Characteristics

• Between each layer of the atmosphere, there is a “pause” that limits mixing between the layers.

• Temperature trends as altitude increases:

  • Troposphere: Decreasing temperature with altitude.

  • Stratosphere: Increasing temperature with altitude due to ozone absorption of UV radiation.

  • Mesosphere: Decreasing temperature with altitude.

  • Thermosphere: Increasing temperature with altitude due to absorption of solar radiation.

  • This trend may be illustrated in diagrams by coloring to depict the heating and cooling transitions.