Welcome to You Ask Andy

Karen Duve, age 12, of West Des Moines, Iowa, for her question:    

HOW MUCH CARBON DIOXIDE IS IN THE AIR?

About 99% of the air is occupied by nitrogen and oxygen. The rest of the airy mixture is a number of rare gases, including carbon dioxide. This gas, as we know, is needed by the entire green plant world to produce its basic food. Yet the supply of carbon dioxide amounts to only 0.03% of the total global atmosphere.


The total weight of the global atmosphere is estimated to be around 5,600 million million tons. This is more than five quadrillion tons, written as figure five plus a string of 15 zeros. Though the atmosphere reaches hundreds of miles above our heads, thinning out as it goes, all but about 1% of its weight is concentrated in the lower layer, within a few miles of the surface.

Almost eight tenths of the general mixture of gases is nitrogen and about one fifth is oxygen.  Most of the rest is argon. Other rare gases in an average air sample include smidgeons of neon, helium, xenon, hydrogen and carbon dioxide.  Surely, one would suppose, this does not leave enough carbon dioxide to support the plant world  which provides food and oxygen for all life on earth.

Actually, the percentages of gases in the air can be somewhat misleading because the global atmosphere is so enormous. For example, the 0.03% of carbon dioxide amounts to around 2 million million tons. What's more, carbon dioxide is heavier than the airy mixture and almost all of it is concentrated in the lower level, where plants can reach it.

The carbon dioxide molecule is a package of two atoms of carbon and one of oxygen  and almost always it is on a recycling mission. It is the waste gas given off by plants and animals. It spreads out to mingle with the other gases of the air and breezes waft it around the globe. Plants absorb it to manufacture their food  and its oxygen atoms are returned to the air.

True, the percentage of carbon dioxide seems quite small. But obviously there is enough of it to support the plant world  which supports all life on the planet earth.  The secret lies in a global recycling project. Day and night, both plants and animals give off waste carbon dioxide. During the daylight hours, plants on land and ocean use the waste carbon dioxide to make their food  and return its oxygen to the air.

 

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