In the second-released Star Wars film, The Empire Strikes Back (1980), a “cloud city” of magnificent structures, filled with active intelligent beings, was portrayed floating in the atmosphere of the giant planet Bespin. If we can re-portray it down a few orders of magnitude, something like that exists right here at planet Earth: whole ecosystems of machinery, active structures, and complex ecosystems in the droplets of clouds.

It’s surprising no one ever checked this before in detail. There were hints that microbes could become airborne or “aerosolized” and take flight in the clouds, but how many are there? What types regularly inhabit cloud droplets? How do they survive, and what do they do? A team of nine from CNRS, the National Center for Scientific Research in France, decided to find out. Their results, published in PLOS ONE, could initiate a whole new science of global “cloud ecology,” the results of which can only be imagined.

Within the atmospheric system, clouds are genuine atmospheric interfaces with the ground: they physically connect high altitudes with the surface by being to a large extent at the origin of wet deposition of aerosols, including microorganisms. Cloud water is a complex mixture of soluble gas and particles dissolved into millions of micron-sized water droplets, and forming very reactive and dynamic systems…. As non-soluble biological particles, some microorganisms can physically impact clouds by acting as embryos for the formation of water droplets and ice crystals, with subsequent impacts on hydrological cycles. Observations of microbiological features in fog and clouds raised the possibility that these also represent habitats for microorganisms, where they would actively take part in the chemical reactivity through metabolic activity and nutrient utilization. So far these active inhabitants of clouds remain largely unknown. [Emphasis added.]

What they found was truly astonishing, calling to remembrance Leeuwenhoek’s first observation in 1665 of a world of microbes in a drop of water. Now, some 350 years later, science has discovered another unseen world of living creatures. In 2013, the team collected three samples from a mountaintop in France in sterile collectors, quickly flash-freezing the material for later analysis. It’s taken a long time to search through the genomes of microbes, because there were so many of them. DNA and RNA sequencing allowed them to make these initial determinations:

Here, microbial communities in cloud water collected at puy de Dôme Mountain’s meteorological station (1465 m altitude, France) were fixed upon sampling and examined by high-throughput sequencing from DNA and RNA extracts, so as to identify active species among community members. Communities consisted of ~10³−10⁴ bacteria and archaea mL^-1 and ~10²−10³ eukaryote cells mL^-1. They appeared extremely rich, with more than 28,000 distinct species detected in bacteria and 2,600 in eukaryotes. Proteobacteria and Bacteroidetes largely dominated in bacteria, while eukaryotes were essentially distributed among Fungi, Stramenopiles and Alveolata. Within these complex communities, the active members of cloud microbiota were identified as Alpha- (Sphingomonadales, Rhodospirillales and Rhizobiales), Beta- (Burkholderiales) and Gamma-Proteobacteria (Pseudomonadales). These groups of bacteria usually classified as epiphytic are probably the best candidates for interfering with abiotic chemical processes in clouds, and the most prone to successful aerial dispersion.

This could change your cloud viewing forever. Up there in those drifting puffs of white, tens of thousands of complex organisms live in cloud cities! There are a hundred to a thousand eukaryotic cells per milliliter, and a thousand to ten thousand bacteria and archaea. These numbers vastly exceed cell counts from previous observations. “Clouds are extremely rich and diverse mosaics of multiple sources ecosystems,” the researchers say.

What are the microbes doing up there? Well, as the authors indicated, they modify the weather. They can act as embryos for the formation of water droplets (think rain) and ice crystals (think snow and sleet). In a real sense, they are natural cloud seeders that can influence the life of the rest of the organisms on earth. Now there’s a good science project for someone in the tradition of Michael Denton and Privileged Species: To what extent is weather regulated by the presence or absence of microbes in the clouds?

Another thing they do is migrate. Catching the cloud trains in the sky, microbes can distribute themselves around the globe. Since all multicellular organisms (including humans) carry numerous microbes around with them, this could be a means of ensuring beneficial microbes are available in every habitat. Of course, it cannot rule out the spread of pathogens, too, but those represent a small fraction of microbes as a whole.

A survey of this type cannot hope to find all the functions of the cloud-city ecosystem, and the authors admit there’s a lot to learn:

Their identification certainly helps understanding the atmosphere as a habitat; it will also allow focusing researches for evaluating microbial impact on cloud physical and chemical processes, but their actual functioning, the “what do they do?” question remains to be answered.

Nevertheless, the authors suspect that these ecosystems engage in significant functions. They speak of the “global functioning of the community” and describe their interactions as a system:

If an abundant group was to be lost from the community, i.e. a group that is likely to contribute significantly to the structure and global functioning of the system, there would be a high probability to lose or reduce also the functions associated with it. This ecological theory, that functional stability implies even structure, derives from established ecosystems and it is applied here for apprehending the functioning of cloud’s microbial communities in the frame of clouds as microbial habitats hypothesis; it is possible though that this is not applicable to environments acting mainly as transport areas, where microbial establishment is by essence not possible, like clouds.

Transport areas can be places of function. Business meetings are held on cruise ships. People interact (sometimes) on subway trains. As long as the cloud community in a droplet of water has the resources it needs, it could carry on whatever functions it is capable of, the nature and extent of which remain to be discovered.

A big question for design advocates might concern whether microbes are necessary for habitability. Microbes may not be necessary for weather (Cassini scientists, for instance, inferred that cloudbursts occur on Saturn’s moon Titan), but perhaps microbes regulate the climate of a planet in some way. It’s too early to predict exactly what functions of this newly discovered “system” will present to the health of the planet, but it surely looks promising. Maybe astrobiologists should not rush to declare exoplanets habitable till the “global functioning of the community” of microbes is better understood.

For the time being, though, we can certainly marvel at the fact that what appeared to be largely a domain of lifeless dust and water up there turns out to be perfused with huge amounts of complex specified information: the genetic codes of tens of thousands of organisms. It wouldn’t be surprising to learn that all that information is there for a purpose. We encourage design-friendly scientists to take this information and extend our understanding into the next big question: “What do they do?”

Photo credit: cocoparisienne, via Pixabay.