Life in the Clouds

Terrestrial life exists in many unexpected places. One variety of tiny plant survives in hot sulfuric acid; others flourish at 9DEGF. below zero. One species of algae grows only among the hairs of the three-toed sloth; another rides the backs of turtles. Now it appears that even clouds floating through the earth's atmosphere provide a precarious home for tiny organisms. Microbiologist Bruce Parker of Virginia Polytechnic Institute, writing in Natural History, argues that tiny animals and plants are feeding, growing and even reproducing high in the sky.

Parker came upon his evidence quite by accident. To aid in a study of water pollution in St. Louis two years ago, he invented a device that could measure pollutants and nutrients in water. He set the instrument in his goldfish pond and found that after a rainfall, particularly after a thunderstorm, the amount of free nutrients (vitamin B12, for example) in the water suddenly increased. Because such substances are normally associated with living organisms, Parker could not imagine why they should be present in rainwater--"unless there is something going on up there."

To check whether life processes were indeed occurring above the earth, he used a chemical called TTC, which changes rapidly from pale yellow to pink when attacked by the enzymes produced in active, living cells. If spores and other dormant forms of life were the only inhabitants of clouds, as most scientists have assumed, they would not become active and respond to the test for at least an hour. But when Parker collected airborne and presumably dormant samples of bacteria, algae and fungi and doused them with TTC, the chemical began turning pink in only 15 to 20 minutes the time it usually takes active cells to react. As a double check, he placed some of the samples in containers of radioactively labeled carbon dioxide. When exposed to light, the algal cells immediately began taking up carbon dioxide, proof that photosynthesis was under way and that the plants were not dormant.

Thriving on Smog. How could minute plants live in a cloud? Many of them, Parker decided, are large enough to act as nuclei for slowly condensing droplets of water--an essential ingredient for all earthly life. The tiny organisms also have an amazingly varied diet available even in unpolluted clouds: oxygen, nitrogen, carbon dioxide, ammonium, nitrogen oxides, sulfur dioxide, carbon monoxide, methane, butane and acetone. Such necessary minerals as potassium, phosphorus, calcium, iron and magnesium could be transported to the clouds in airborne soil and dust particles.

If life in the clouds is as widespread as Parker suspects, biologists will have whole new ecological possibilities to explore. Clouds may well spread disease, for example, by harboring harmful viruses or bacteria. On the other hand, organisms that thrive on the ingredients of smog and smoke could help in the fight against air pollution. Introduced into clouds, they would feed on the undesirable gases and particles, thus converting pollution into harmless cloud creatures.

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