In what is believed to be the first study of its kind, researchers used genomic techniques to document the presence of significant numbers of living microorganisms -- principally bacteria -- in the middle and upper troposphere（对流层）, that section of the atmosphere approximately four to six miles above Earth's surface. Whether the microorganisms routinely inhabit this portion of the atmosphere -- perhaps living on carbon compounds also found there -- or whether they were simply lofted there from Earth's surface isn't yet known. The finding is of interest to atmospheric scientists, because the microorganisms could play a role in forming ice that may impact weather and climate. Long-distance transport of the bacteria could also be of interest for disease transmission models.

The microorganisms were documented in air samples taken as part of NASA's Genesis and Rapid Intensification Processes (GRIP) program to study low- and high-altitude air masses associated with tropical storms. The sampling was done from a DC-8 aircraft over both land and ocean, including the Caribbean Sea and portions of the Atlantic Ocean. The sampling took place before, during and after two major tropical hurricanes -- Earl and Karl -- in 2010.

The research, which has been supported by NASA and the National Science Foundation, was scheduled to be published online January 28th by the journal Proceedings of the National Academy of Sciences.

"We did not expect to find so many microorganisms in the troposphere, which is considered a difficult environment for life," said Kostas Konstantinidis, an assistant professor in the School of Civil and Environmental Engineering at the Georgia Institute of Technology. "There seems to be quite a diversity of species, but not all bacteria make it into the upper troposphere."