ecosystems do not address time or the life cycle of an ecosystem, the influence of
time on ecosystem variability and organism-specific viability was presented in
Henry C. Cowles’ concept of ecological succession (Cowles 1899). Ecological
succession studies have just recently been applied to the micro-scale of microorganisms, but historically, most have occurred at the macro-scale of plants and animals,
and on temporal scales of decades to millions of years (Ortiz-Alvarez et al. 2018;
Walker et al. 2010).
I recall walking into a meeting room for a graduate-level course on molecular
paleontology, being taught by a geology faculty member at the University of South
Florida, and marveling at the geological timeline tape that extended around the
ceiling trim. The segment of that tape that represents the existence of the only literate
organism to have ever existed on the planet is just a tick (the last ~200,000 years) at
the end of the very long ~4.5 billion-year timeline. The few other students in the
class had backgrounds in geology versus my background in microbiology. What
struck me as the course progressed was the differences in how we thought about
time. The geologists commonly thought in terms of millions to billions of years
whether it was referencing subjects such as evolution (humans and our atmosphere),
extinction events, or continental drift. As a microbiologist I was keenly aware of
theories on the evolution of life, like Cairns-Smith’s “clay hypothesis” (CairnsSmith and Hartman 1986), but I spend the majority of my time in the realm of
public health microbiology where microbial replication and pathogenic outbreaks
occur over periods of minutes, hours, and days. There is no doubt that both
inorganics and organics contribute to the definition of an ecosystem, but all ecosystems as we know of them have one thing in common; they are evanescent in nature.
It is only the stability of an ecosystem in relation to time that defines that system’s
degree of evanescence.
Micro-aerobiology or the study of microbial life in the atmosphere was pioneered
by Louis Pasteur. In Pasteur’s efforts to dispel the theory of “Spontaneous Generation,” he demonstrated the presence of microbial life in atmospheric samples
collected in caves, on mountain tops, and within the built environment (Pasteur
1861). Irish scientist John Tyndall, a supporter of Pasteur, later described the results
of nutrient broth tray experiments utilized to detect viable microbial life in the
atmosphere: “Reflecting on the whole of this, I conclude that the germs float through
the atmosphere in groups or clouds, and that now and then a cloud specifically
different from the prevalent ones is wafted through the air. The touching of a
nutritive fluid by a Bacterial cloud would naturally have a different effect from the
touching of it by the sterile air between two clouds. But, as in the case of the mottled
sky, the various portions of the landscape are successively visited by shade, so, in the
long run, are the various tubes of our tray touched by the Bacterial clouds, the final
fertilization or infection of them all being the consequence.” (Tyndall 1882). This
early research that discovered that microorganisms can routinely be found in the
atmosphere and that their distributions are not universal, but patchy, was key to
understanding variance in their concentrations due to such factors as location and
altitude constraints. More recent culture- and molecular-based studies have demonstrated that very diverse microbial communities routinely occur in Earth’s
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D. W. Griffin
time on ecosystem variability and organism-specific viability was presented in
Henry C. Cowles’ concept of ecological succession (Cowles 1899). Ecological
succession studies have just recently been applied to the micro-scale of microorganisms, but historically, most have occurred at the macro-scale of plants and animals,
and on temporal scales of decades to millions of years (Ortiz-Alvarez et al. 2018;
Walker et al. 2010).
I recall walking into a meeting room for a graduate-level course on molecular
paleontology, being taught by a geology faculty member at the University of South
Florida, and marveling at the geological timeline tape that extended around the
ceiling trim. The segment of that tape that represents the existence of the only literate
organism to have ever existed on the planet is just a tick (the last ~200,000 years) at
the end of the very long ~4.5 billion-year timeline. The few other students in the
class had backgrounds in geology versus my background in microbiology. What
struck me as the course progressed was the differences in how we thought about
time. The geologists commonly thought in terms of millions to billions of years
whether it was referencing subjects such as evolution (humans and our atmosphere),
extinction events, or continental drift. As a microbiologist I was keenly aware of
theories on the evolution of life, like Cairns-Smith’s “clay hypothesis” (CairnsSmith and Hartman 1986), but I spend the majority of my time in the realm of
public health microbiology where microbial replication and pathogenic outbreaks
occur over periods of minutes, hours, and days. There is no doubt that both
inorganics and organics contribute to the definition of an ecosystem, but all ecosystems as we know of them have one thing in common; they are evanescent in nature.
It is only the stability of an ecosystem in relation to time that defines that system’s
degree of evanescence.
Micro-aerobiology or the study of microbial life in the atmosphere was pioneered
by Louis Pasteur. In Pasteur’s efforts to dispel the theory of “Spontaneous Generation,” he demonstrated the presence of microbial life in atmospheric samples
collected in caves, on mountain tops, and within the built environment (Pasteur
1861). Irish scientist John Tyndall, a supporter of Pasteur, later described the results
of nutrient broth tray experiments utilized to detect viable microbial life in the
atmosphere: “Reflecting on the whole of this, I conclude that the germs float through
the atmosphere in groups or clouds, and that now and then a cloud specifically
different from the prevalent ones is wafted through the air. The touching of a
nutritive fluid by a Bacterial cloud would naturally have a different effect from the
touching of it by the sterile air between two clouds. But, as in the case of the mottled
sky, the various portions of the landscape are successively visited by shade, so, in the
long run, are the various tubes of our tray touched by the Bacterial clouds, the final
fertilization or infection of them all being the consequence.” (Tyndall 1882). This
early research that discovered that microorganisms can routinely be found in the
atmosphere and that their distributions are not universal, but patchy, was key to
understanding variance in their concentrations due to such factors as location and
altitude constraints. More recent culture- and molecular-based studies have demonstrated that very diverse microbial communities routinely occur in Earth’s
106
D. W. Griffin