The rest of the gases are minor components but sometimes are very important. Nitrogen and oxygen together make up 99 percent of the planet’s atmosphere. Atmospheric Gases Figure 15.1 Pie chart of Earth’s atmospheric composition. Important greenhouse gases include carbon dioxide, methane, water vapor, and ozone. Without an atmosphere with greenhouse gases, Earth’s temperatures would be frigid at night and scorching during the day.
Greenhouse gases trap heat in the atmosphere so they help to moderate global temperatures. The Atmosphere Moderates Earth’s TemperatureĪlong with the oceans, the atmosphere keeps Earth’s temperatures within an acceptable range. Without ozone for protection, only the simplest life forms would be able to live on Earth. This protects living things on Earth’s surface from the Sun’s most harmful rays. Ozone in the upper atmosphere absorbs high-energy ultraviolet (UV) radiation coming from the Sun. Ozone is a molecule composed of three oxygen atoms, (O 3). Thus, life depends on the climate and weather that occur in the zones in which life occurs. Drier areas may have species of plants and animals that have strategies that allow them to thrive whereas more temperate areas that have more moisture have species that would not fare as well in drier climates. Species are adapted to the conditions in which they live. Areas that are prone to regularly-occurring water-rich storms have quite different ecosystems than drier areas that receive less moisture.
The amount of water vapor present in different areas of the planet has a dynamic effect on the weather that occurs in different areas. All weather takes place in the atmosphere, and virtually all of it happens in the lower atmosphere. Water spends a lot of time in the atmosphere, mostly as water vapor. The relationship between the atmosphere and water vapor is a crucial part of the hydrologic cycle, which we discussed in Chapter 10.1. Plants also go through respiration and consume some of the sugars they produce. In respiration, animals use oxygen to convert sugar into food energy they can use. Photosynthesis is responsible for nearly all of the oxygen currently found in the atmosphere. By creating oxygen and food, plants have made an environment that is favorable for animals. In photosynthesis plants use CO 2 and create O 2.
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