Abstract
The Earth's atmosphere is an extremely large and sparse environment which is quite challenging for the survival of microorganisms. We have long wondered about the limits to life in the atmosphere, starting with Leeuwenhoek's observation of "animalcules" collected from the air. In the past century, significant progress has been made to capture and identify biological material from varying elevations, from a few meters above ground level, to the clouds near mountaintops, and the jet streams, the ozone layer, and even higher up in the stratosphere. Collection and detection techniques have been developed and advanced in order to assess the potential diversity of life from very high altitudes. Studies of microbial life in the stratosphere with its multiple stressors (cold, dry, irradiated, with low pressure and limited nutrients), have recently garnered considerable attention. Here, we review studies of Earth's atmosphere, with emphasis on the stratosphere, addressing implications for astrobiology, the dispersal of microbes around our planet, planetary protection, and climate change.
Highlights
Why is it important to study and understand the limits to life at the highest elevations in the atmosphere? Elevation is a limit to life that has not yet been fully explored
We focus on conditions in the upper atmosphere, especially the stratosphere (Figure 1), and primarily on what is known about how microorganisms can survive there, under extreme conditions
Astrobiology research has utilized Earth's stratosphere and its conditions as an analogue to conditions found on Mars, addressing whether extremophilic and other hardy microorganisms that survive in the stratosphere may tolerate conditions on the surface of Earth's sister planet
Summary
Why is it important to study and understand the limits to life at the highest elevations in the atmosphere? Elevation is a limit to life that has not yet been fully explored. A manned US high-altitude balloon, Explorer II, became the first air sampling mission to reach the stratosphere (up to 21 km ASL), and several viable microbes were isolated within the genera caister.com/cimb A. Imshenetsky and colleagues collected samples of air from even higher elevations, from the stratosphere to the mesosphere (48-85 km ASL), using γ-radiation sterilized meteorological rockets and investigated the characteristics of the bacterial and fungal strains isolated.
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