about 99 of air comprises
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Nitrogen and oxygen make up about 99 percent of Earth's air. People and other animals need oxygen to live. Carbon dioxide, a gas that plants depend on, makes up less than .21-Jan-2011
nitrogen and oxygen
Answer:
Nitrogen and oxygen make up about 99 percent of Earth’s air. People and other animals need oxygen to live. Carbon dioxide, a gas that plants depend on, makes up less than .
Plants and animals each produce the gases that the other needs to live. Plants need carbon dioxide—people and other animals exhale carbon dioxide as a waste product. People and other animals need oxygen—plants produce oxygen during an important process called photosynthesis, which turns the sun’s energy into nutrients.
Water vapor in the air is sometimes visible as clouds. Water enters the atmosphere through the water cycle. The water cycle also brings molecules in the air into oceans, lakes, and rivers.
Some gases in the air come from volcanic eruptions. Volcanic eruptions eject gases from the interior of the Earth. The most common gas emitted by volcanoes is water vapor. Other gases, such as carbon monoxide and sulfur dioxide, are toxic to most organisms. A few organisms, however, thrive on these gases. At the bottom of the ocean are bacteria that do not need oxygen or sunlight to survive. In other words, they do not need air. These strange organisms create their own nutrients using hydrogen sulfide, not carbon dioxide. The hydrogen sulfide comes from cracks, or vents, in the Earth’s crust.