The Breath of Life

The earth is wrapped in a thin, loose shell of gases - which we call the atmosphere. The mix of gases that make up the atmosphere has changed greatly over the eons.

A Flemish alchemist and physician named Johann Baptista van Helmont was the first man to discover that the air we breathe is not one single substance but a mixture of substances. In a manuscript published after his death in 1644, he argued, based on his experiments, that an invisible "spirit" curled from every one of the bubbling flasks in his alchemical laboratory, and from each of the red coals in his furnaces. "I call this Spirit, unknown hitherto, by the new name of Gas," he wrote - coining the word from the Flemish pronunciation of the Greek word "chaos." One of the gases that he discovered was carbon dioxide, a gas that is now creating chaos on a global level.

Since van Helmont's discovery, we have come to realize, through scientific experimentation and persistent measurements, that carbon dioxide is almost everywhere. By the 1950s, Charles Keeling, working under the auspices of the California Institute of Technology, began extensive tracking of carbon dioxide levels on the planet. He recognized a pattern that had eluded others: the carbon dioxide concentration always dropped as the sun rose in the sky, and then in- creased as the sun went down. The count stayed high all night, bottomed out in the afternoon, and began climbing again after sundown.

The life cycle was becoming more and more obvious to the scientific community: every day, as the sun rises, every green thing on the planet - from skunk cabbage to club moss - begins inhaling carbon dioxide, for use in photosynthesis. As the plants inhale, the amount of gas in the air begins to drop.

Photosynthesis is, literally, "building with light." The building process takes place inside plant cells within organelles call chloroplasts. Inside each choloroplast, plants break apart molecules of carbon dioxide into carbon and oxygen. They also break water molecules into hydrogen and oxygen. Then they put most of these atoms back together in new combinations to build simple sugars like glucose, throwing out some of the oxygen as "trash." The process requires steady supplies of sunlight for energy, and steady supplies of carbon dioxide and water for raw materials.

By afternoon, plants have taken a good deal of carbon dioxide out of the atmosphere. At the same time, however, the plants are busily eating the sugars they have made for themselves. This is the metabolic process of respiration. Respiration means literally "to breathe back, to blow back;" it is a form of combustion, a very slow burn which consumes oxygen and produces carbon dioxide.

Photosynthesis and respiration are two of the most fundamental processes of life on Earth, and they run in opposite directions. Photosynthesis takes in carbon dioxide and releases oxygen; respiration takes in oxygen and releases carbon di- oxide. The two processes also run on different timetables: photosynthesis works a day shift, because the process requires sunlight and most plants take in carbon dioxide only when the sun shines. The gas enters the plant through a myriad of microscopic pores, stomata, on the underside of each green leaf. These little doors open at sunrise and close at sundown on every plant on the planet.

Respiration, on the other hand, works both a day shift and a night shift. At four o'clock in the morning - while the stomata are closed and green leaves are taking in virtually no carbon dioxide - the leaves are still respiring, blowing back carbon dioxide to the air. At the close of most twenty-four hour periods, most plants have "borrowed from and returned to" the atmosphere about the same amount of carbon dioxide.

This "breathing cycle" is apparent throughout the plant life on the planet: plants and trees breathe once a day. (Animals, including people, aren't a natural part of this cycle. They have no cholorplasts, so they get their energy and their raw materials by eating plants, and by eating the animals that have eaten plants, and by inhaling the oxygen released by plants.)

So?

So this natural breathing cycle of the earth's plant life is a major factor in one of the major ecological problems facing the planet: the greenhouse effect.

It is the atmosphere that keeps us warm; outer space is a very cold place, and it is the layers of gases that wrap the planet that protect us from freezing. In this sense, the Earth's gases are like the glass walls of a gree