Study Notes on Layers of the Atmosphere

Environmental Science: Layers of the Atmosphere

Lesson Objectives

  • At the end of the lesson, students are expected to:

    • O1: Define the term "atmosphere".

    • O2: List the layers of the atmosphere.

    • O3: Describe the features of each layer.

Lesson Flow

  1. Definition of Atmosphere

  2. Structure of the Earth's Atmosphere

  3. Layers of the Atmosphere

What is Atmosphere?

  • The atmosphere refers to the layer of gases that surrounds the Earth.

    • Composition:

    • Mainly consists of nitrogen (N₂) and oxygen (O₂), along with small amounts of other gases.

    • Functions:

    • Provides vital protection for life on Earth.

    • Regulates temperature.

    • Supports weather and climate systems.

Layers of Earth's Atmosphere

  • The Earth's atmosphere is divided into five primary layers:

    • Troposphere

    • Stratosphere

    • Mesosphere

    • Thermosphere

    • Exosphere

Detailed Description of Each Layer

Troposphere

  • Altitude: 0 - 12 km

  • Characteristics:

    • It is the lowest layer of Earth's atmosphere.

    • Extends from the Earth's surface to an average altitude of about 12 kilometers.

    • It is the layer where weather occurs, and where all human life exists.

    • Hot air balloons and airplanes fly within this layer due to adequate conditions for safe and efficient air travel.

Stratosphere

  • Altitude: 12 - 50 km

  • Characteristics:

    • Located above the troposphere, this layer extends from about 12 kilometers to 50 kilometers above the Earth's surface.

    • It contains the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun.

    • Radiosondes, instruments used for weather observation, can collect data and ascend into the lower part of this layer.

Mesosphere

  • Altitude: 50 - 80 km

  • Characteristics:

    • The third layer of Earth's atmosphere.

    • Extends roughly from 50 kilometers to 85 kilometers above the Earth's surface.

    • Characterized by thin air and low atmospheric pressure.

    • This is the layer where meteors burn upon entering the atmosphere, creating the visual phenomenon known as shooting stars.

Thermosphere

  • Altitude: 80 - 700 km

  • Characteristics:

    • The fourth layer, beginning at approximately 85 kilometers with no clearly defined upper boundary.

    • Composed primarily of individual gas molecules, notably oxygen and nitrogen, in contrast to molecular combinations.

    • This layer is also where auroras occur, including the Northern Lights and the Southern Lights.

Exosphere

  • Altitude: 700 - 10,000 km

  • Characteristics:

    • The outermost layer of Earth's atmosphere, located above the thermosphere.

    • It gradually transitions into the vacuum of space.

    • This layer contains satellites and other human-made objects in Earth's orbit.

    • Satellites are placed in orbit within the exosphere to carry out various functions.

Ozone Layer

  • The ozone layer is situated between 10-31 miles (approximately 16-50 km) above the Earth’s surface within the stratosphere.

  • Function:

    • Ozone gas here protects life on Earth by absorbing high-energy ultraviolet (UV) radiation from the Sun.

    • It prevents sunburns and potential genetic damage (mutations) that can lead to diseases such as skin cancer.

Chemical Composition and Reactions of Ozone

  • Ozone is comprised of three oxygen atoms ( ext{O}_3).

  • Formation:

    • Ozone forms when ultraviolet sunlight breaks apart oxygen molecules ( ext{O}_2) and free oxygen atoms then recombine with other ext{O}_2 molecules to create ext{O}_3.

  • Destruction:

    • Ozone can be destroyed when it reacts with other molecules, including nitrogen (N), hydrogen (H), chlorine (Cl), and bromine (Br).

Human Impact on the Ozone Layer

  • Human-made chemicals known as chlorofluorocarbons (CFCs), developed in the 1960s, are significant contributors to ozone depletion.

    • CFCs are utilized in various products, including air conditioners, aerosol spray cans, and Styrofoam manufacturing.

Historical Context on Ozone Depletion

  • By the 1980s, scientists discovered that CFCs were damaging the ozone layer, primarily through chlorine atoms breaking apart ozone molecules.

  • In 1986, more than 70 countries signed the Montreal Protocol to reduce CFC production.

    • Global cooperation and actions taken through this protocol have permitted the amount of stratospheric ozone to gradually recover.

Ozone Types and Levels

  • UV Types:

    • UV-A: Longest wavelength, less harmful.

    • UV-B: Intermediate wavelength, more harmful.

    • UV-C: Shortest wavelength, most harmful, but largely absorbed by ozone.

  • Stratospheric Ozone (ozone layer)

    • Located at 10-31 miles above Earth.

  • Surface-Level Ozone (SMOG)

    • Created by chemical reactions involving air pollutants from burning fossil fuels and various industrial processes.

    • Harmful to life and distinctly different from the protective stratospheric ozone.