Earth's Atmosphere

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Looking Ahead

You will learn in the upcoming Global Climate Change and Spirituality section that in some religions the air we breathe is a spiritual symbol of the breath of God.

Weather and climate take place in Earth’s atmosphere, which is the thin layer of gases surrounding Earth that is held in place by Earth’s gravity. Without the atmosphere, life on Earth could not exist. It contains the oxygen we breathe, helps warm the Earth, shields us from the sun’s harmful ultraviolet radiation (UV), and is a vital part of the water cycle as was discussed in the Water Chapter.

The atmosphere is made up of a mixture of different gases, minute water droplets, and tiny suspended solid particles (see Table 1). Some of these components are considered permanent components, while others are variable. Permanent components, such as nitrogen and oxygen, are characterized by their stable and consistent presence in the atmosphere at any given time. However, the presence and amount of variable components, such as water vapor, can fluctuate depending on different factors that will be further discussed below.

Compared with the radius of Earth, the depth or thickness of Earth’s atmosphere is very thin. More than 99% of the gaseous molecules (by mass) which make up the Earth’s atmosphere are found in the 50 kilometer thick layer closest to the surface of the Earth (see Figure 1).

Figure 1: The Earth’s atmosphere is a relatively thin and fragile layer of gases- a. an artist’s depiction, b. a satellite image: the thin blue band of gas seen here hovering above the surface of the earth is our fragile atmosphere. Within this band, which is only 50km thick, occur 99.8% of the molecules of gas that support and protect all forms of live on earth. 1

Looking Ahead

You will learn in the upcoming Global Climate Change and Ethics section that Earth’s atmosphere has intrinsic value. Here, you see the reason why: a healthy atmosphere is necessary for all life on Earth.

The two most abundant gases in the Earth’s atmosphere are nitrogen (N2), which makes up 78% of the volume of the atmosphere, and oxygen (O2), which makes up 21%. Although nitrogen and oxygen together with the other permanent gases account for nearly the entire atmosphere (>99%), and are crucial for life on Earth, they have little to no impact on weather and climate. It is the scarce variable components, like water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) that influence weather and climate.

Is ozone helpful or harmful?
Ozone that occurs in the stratosphere, tens of kilometers away from the earth’s surface, is critical to protecting life on Earth by blocking harmful UV radiation from the sun. On the other hand, ozone that forms at the earth’s surface due to human activities like industrial and motor vehicle emissions, is a very strong oxidant and direct exposure is harmful to plants, animals, microorganisms, and humans.

Water vapor is the most abundant of the atmosphere’s variable components. Its concentration changes from time to time and from place to place. On average, water vapor comprises 0.25% of the atmosphere. As discussed in the Water Chapter, the hydrologic cycle forms clouds from water vapor and produces precipitation that replenishes water in soils, lakes, and rivers. This condensation process (the cooling of water vapor to form liquid water) also releases stored heat, which plays an important role in the development of storms. In these ways, water vapor plays a critical role in weather.

Figure 2. A greenhouse is made of glass or plastic windows. Sunlight passes through the windows but heat is trapped inside. Vegetables and flowers can grow even during colder months.1

Other gases among the atmosphere’s variable components are present in very small amounts, yet can have a powerful influence on weather. In some cases these trace variable gases are also extremely important to life on Earth.

Looking Ahead

In the Global Climate Change and Spirituality section you will learn that spiritual traditions such as Hinduism and Islam believe that the interdependent relationship between the atmosphere, plants, animals, water, and soil is a sacred balance.

For example, ozone, which naturally occurs in the stratosphere (10-50 km altitude in the atmosphere) screens out the sun’s ultraviolet radiation (UV) which would otherwise reach the Earth’s surface at levels damaging to living organisms. The screening of UV radiation occurs at very low concentrations of ozone (0.000004%). Ozone is also one of the greenhouse gases (GHGs), and has a strong influence on global warming.

Similarly, carbon dioxide makes up only 0.04% of the atmosphere, but is an important greenhouse gas that contributes to the warming of the Earth, and is also essential for photosynthesis, supplying plants and animals with their ultimate source of carbon.