The idea that life can be found in the air and clouds is not a new one. For decades biologists have been sticking vials into the slip stream of airplanes, even kites, or cracking open Petri dishes in hot-air balloons, and on mountaintops. While such efforts always yield evidence of microscopic life (mainly bacteria), it was assumed that such life was an accidental passenger in the air having been blown aloft from the surface of the land or perhaps breaking bubbles of churning sea water. That idea apparently needs revising.
Does Life Exist in the Clouds?
In the late 1990s, evolutionary biologist William Hamilton began a collaboration with then PhD candidate Timothy Lenton to explore the possibility that microbes not only reside permanently in clouds but that they somehow assist in the formation of the clouds in which they live. Hamilton and Lenton published their theory in 1998.
As Robert R. Dunn quips in an article entitled, ”A Head in the Clouds,” in the July/August 2009 issue of Natural History, “Their paper was ahead of its time. The question it raised was too big for microbiologists, too biological for climatologists, and too airy for oceanographers.” With Hamilton’s death in 2000 from malaria contracted on a trip to the Congo, his ideas about life in the clouds were promptly dismissed. Scientists have begun to discover that not only is life found in the air and clouds, it thrives there apparently using organic acids and alcohol, sulfur, and nitrogen as “food.”
Known as aeroplankton (or aerial plankton), aerial life forms comprise about 1,000 different species of bacteria, 40,000 species of fungi, hundreds of species of protists including algae and other small water-borne organisms. Algae may seem a puzzling member of the aeroplankton until one realizes that a large cloud has about as much water as a shallow lake of the same geographic size.
Also found are mosses and liverworts that spend at least part of their life cycle in the atmosphere in the form of spores. Pollen and tiny seeds from flowering plants are often temporary passengers on the air as are arthropods like tiny insects and small spiders.
Recently three new species of bacteria were found in the stratosphere, more than twelve miles above the earth. None of these species has ever been collected anywhere else raising the interesting and distinct possibility that some life forms live permanently in the air and clouds.
The Emerging Discipline of Aeroecology
While the field of aerobiology does exist, it has traditionally been concerned primarily with the medical aspects of transmission of airborne diseases caused by bacteria and viruses. Recently, a branch of aerobiology known as aeroecology has begun to emerge.
Aeroecologists study how airborne organisms – microbes, bats, birds, and arthropods – function and survive in the atmosphere (or aerosphere) and clouds. Aeroecology is a multi-disciplinary science that encompasses and integrates aspects of atmospheric science, earth science, geography, ecology, computer science, computational biology, and engineering.
Aeroecologists face three main problems as they attempt to probe the aerosphere:
1. Determining the best methods and techniques for detecting and sampling aeroflora and aerofauna.
2. Determining relevant environmental variables and how to integrate them against the proper temporal and spatial scales.
3. Understanding and interpreting the ecological, behavioral, and evolutionary responses of aerospheric organisms in the context of complex meteorological conditions.
“Appropriate integration of diverse tools and concepts for probing into the lives of organisms aloft can help inform important ecological and evolutionary concepts and management decisions associated with the spread of invasive species, emergence of infectious diseases, altered biodiversity, and sustainability of terrestrial, aquatic, and aerospheric environments."
(Thomas H. Kunz, Director of the Center for Ecology and Conservation Biology)
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