Vocabulary

environmental science geosphere hydrosphere atmosphere biosphere ozone layer greenhouse effect biodiversity species diversity genetic diversity figure 22-1

Layers of air (atmosphere), water (hydrosphere), and rock and soil (geosphere) interact with each other. Living things make up the biosphere, which includes parts of each of these three layers.

Atmosphere (about 1,000 km thick)

Hydrosphere 29 km -p

Biosphere 20 km

9 km

11 km

Atmosphere (about 1,000 km thick)

Geosphere (6,378 km radius)

Word Roots and Origins ozone from the Greek ozein, meaning "to smell"

figure 22-2

Gases in Earth's atmosphere trap heat near the planet's surface just as the panes of glass on a greenhouse trap heat. Solar energy is trapped near the Earth's surface by greenhouse gases such as carbon dioxide and methane.

Atmosphere

The atmosphere consists of about 78 percent nitrogen, N2, about 21 percent oxygen, O2, and about 1 percent other gases, including water vapor, H2O, and carbon dioxide, CO2. Atmospheric gases become less dense at greater altitudes. For example, the density (number of molecules per liter) of oxygen at 18,000 ft is half of its density at sea level. While the density of each gas decreases with altitude, the relative proportion of each gas remains about the same. An exception is ozone (OH-zohn), O3, a naturally occurring gas that is vital to life on Earth. The concentration of ozone is greatest in the ozone layer, a region that is about 20 km above Earth's surface.

Climate and Atmosphere

The ozone layer is important because it absorbs most of the sun's ultraviolet radiation before it reaches Earth's surface. Most organisms on Earth depend on this protection because ultraviolet radiation can damage DNA and cause mutations. In contrast, some gases in the atmosphere direct energy toward Earth's surface. Energy from the sun reaches Earth's surface as light but may leave the surface as heat. Some gases in the atmosphere function to radiate this heat back toward Earth's surface. The atmosphere's ability to trap heat in this way is called the greenhouse effect. The atmospheric gases that contribute to this effect are sometimes called greenhouse gases.

As Figure 22-2 illustrates, Earth can be heated by sunlight in the same way that air in a greenhouse can be. O First, solar energy passes through the atmosphere and strikes Earth's surface. Some of this light is absorbed and converted to heat. © A portion of the heat radiates back through the atmosphere. © Some of the radiated heat escapes into space. O However, some heat is absorbed by gases in the atmosphere and then radiated back to Earth's surface. As a result, Earth's surface is kept warm.

Traces of water vapor and greenhouse gases in upper atmosphere

^^ Some heat escapes into space.

Some heat is absorbed by greenhouse gases and returned to Earth.

Solar energy penetrates Earth's atmosphere and warms its surface.

Earth

The concentrations of greenhouse gases, such as CO2 and methane, affect the amount of the sun's heat that is trapped by the atmosphere. CO2 cycles between the atmosphere and living things through the processes of photosynthesis and cellular respiration. Additional CO2 enters the atmosphere when organic matter is burned. Increasingly, humans burn organic matter that is in the form of fossil fuels, such as natural gas, coal, and petroleum.

Hydrosphere

When astronauts in space look at Earth, they see a mostly blue planet because oceans cover about 70 percent of Earth's surface. Water is very important to life on Earth. Especially important is freshwater, or water that is not salty and so is suitable for uses such as drinking, bathing, and watering crops. Only about 3 percent of surface water is freshwater, and most of this freshwater is tied up in glaciers at the poles.

Geosphere

The geosphere exchanges materials with the atmosphere, hydrosphere, and biosphere. Recall that photosynthetic organisms take carbon from the atmosphere and incorporate it into living tissue. After the organisms die, some of the carbon may become coal or oil and thus enter the geosphere. Sulfur, phosphorus, and other elements also cycle between the biosphere and geosphere.

Biosphere

The biosphere includes all parts of Earth where life exists. The biosphere includes the part of the atmosphere between Earth's surface and approximately 9 km above the surface, most of the hydrosphere, and at least 11 km of the top crust of the geosphere. Scientists occasionally discover life in new places and thus expand the known boundaries of the biosphere. Attempts to replicate an Earth-like system, such as the project shown in Figure 22-3, have shown that Earth's spheres form a complex and delicately balanced system.

figure 22-3

With an ambitious project in the Arizona desert called Biosphere 2, researchers attempted to build a small, self-contained, Earth-like system that included a biosphere, geosphere, hydrosphere, and atmosphere capable of sustaining human life for long periods. The project encountered many difficulties, showing that Earth's biosphere is not easy to replicate.

Word Roots and Origins biosphere

From the Greek bios, meaning "life," and the Latin sphaera, meaning "globe."

figure 22-3

With an ambitious project in the Arizona desert called Biosphere 2, researchers attempted to build a small, self-contained, Earth-like system that included a biosphere, geosphere, hydrosphere, and atmosphere capable of sustaining human life for long periods. The project encountered many difficulties, showing that Earth's biosphere is not easy to replicate.

www.scilinks.org Topic: Biodiversity Keyword: HM60151

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