What the Skies Are Made of
An Introduction to the Ecosystem of the Atmosphere
“I want to sleep on a cloud!” My younger cousin beamed.
Instead of being met with a series of aaww’s and doe-eyed stares, we, the elder cousins of 8–13 years old, decided to take this opportunity to teach the kid a lesson about science.
“You can’t sleep on a cloud!” We all seemed to scoff in unison.
“Yeah,” someone chimed in, “You’d fall through. Clouds are just water vapor.”
Not to condone crushing childhood dreams, but we weren’t wrong. We were, however, excluding an entire world of science — an ecosystem, that exists way up there.
Why do we have an atmosphere to begin with?
Our 4.6 billion year old planet began it’s start with only a thin atmosphere of hydrogen and helium, and the first thick atmospheric gases were likely included hydrogen sulfide, methane, and tons of carbon dioxide. Yet now, the Earth’s atmosphere is made up of a stew of ‘human friendly’ elements, including about 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and some other elements and compounds found in very small amounts. How did it make such big change?
The answer seems to be in volcanoes. On the molten surface of young Earth, eruptions of active volcanoes released gases. It’s suggested that this is how we got a lot of the nitrogen, a heavy gas that’s hard to shake, in our atmosphere: from volcanic ammonia. As the Earth cooled, the vapor released could be held in position by gravity, an attractive force that exists between all particles.
Around 2.7 billion years ago, the first steps towards creating an aerobic organism-friendly atmosphere were beginning with the evolution of anaerobic bacteria, especially bluish-green cyanobacteria. Through photosynthesis, they used carbon dioxide and sunlight to fuel themselves, and in return, they released oxygen which would eventually transform Earth’s entire atmospheric condition.
In addition to our oxygenated air, the evolution of early Earth left us with water vapor circulating at lower altitudes. This water vapor is a crucial part of our water cycle and has a lot to do with our weather and why clouds exist in the first place.
The clouds themselves to have a pretty basic chemical composition, but the process that makes them look good enough to sleep on are a lot more interesting.
How are clouds formed?
As water evaporates from oceans, lakes and soil, or is spread into the air from the transpiration of plants, the droplets gain altitude in the troposphere — the atmospheric layer closest to Earth’s surface. As the air rises, the temperature gets colder and the air can hold less moisture.
As temperatures lower, molecular motion slows and when they get higher, molecular motion speeds up. When you boil a pot of water, for example, you’re adding heat — a form of energy. That heat can then be turned into kinetic energy (motion) and the water plumes up as steam. When you freeze water, the molecules don’t have as much kinetic energy and they can hold a shape.
The water vapor at higher altitudes collect around particles of dust, pollution, and other particles known by meteorologists as ‘condensation nuclei’, which helps them get larger. When they get together, they form a cloud and can float around in the air, carried by wind currents. When they get too heavy, water droplets or ice crystals can fall back down to the surface and we get rain or a snow.
Not all clouds look like they’d make good bedding. There are a lot of types clouds of varying altitudes, but the ones that look good enough to sleep on are cumulus clouds. They’re puffy and textured and white, which is kind of strange considering they’re made out of water.
How are clouds perceived?
We see clouds as white because of light. Light can exhibit properties of particles and waves, but the wave properties are most interesting for colors. Waves of light have different wavelengths, literally the distance between peaks. These scale down to less than 1/millionth of a meter (a micron).
The water vapor that collects around condensation nuclei in clouds are really small, about 10 microns. But, all the wavelengths of visible light are a lot smaller than this (red light, for example, has a wavelength of about 0.7 microns), so all wavelengths of visible light reflect off the crystals equally and when those colors bombard our eyes, we see white.
As “low clouds”, cumulus clouds tend to be found about 3,300 feet up, but the highest of the high clouds, cirrus clouds, tend to be about 20,000 feet up. So, reasonably, absent the minor issue of gravity, you could survive on a cumulus cloud for a little while. But, you’d still have some health concerns.
How does living the high life affect the body?
It’s often said that the air is “thinner” at higher altitudes because, although the percentage of oxygen stays the same, the air pressure is lower so the molecules are spread around more “thinly.” When there’s a lot of pressure pushing down on our bodies, oxygen has an easier time penetrating them membranes of our lungs and getting to our blood, which then transports the oxygen around the body. That oxygen is necessary for metabolism — making and breaking of molecules needed for energy, brain function, and essentially all of the molecular reactions that keep your running.
If you’re a low altitude dweller like me, you might find yourself panting, and your heart racing, as you climb to higher ground and your body tries to collect enough oxygen to keep you functioning.
At high altitudes, psychological changes in vision, personality, and attentiveness often exist alongside nasty symptoms like dehydration from profuse sweating, sleep apnea, trouble sleeping, and reduced physical fitness.
Despite the potential to lose consciousness, you probably wouldn’t be in life threatening danger just by visiting a reasonably low mountain top. The body has short and long term adaptions to high altitudes, some of which even lead to genetic and physiological changes in populations.
If you wanted to lay in the hammock like arms of cirrus cloud, however, you’d probably die. At 26,000 feet up, the so called “death zone” to mountaineers, it’s thought that no human could survive long enough to successfully adapt.
What is the ecosystem of the skies?
Microbes have made a habit of living places humans can’t. Their relatively simple structure, and rapid rate of reproduction allows them to diversify and adapt exceptionally well. They’ve even been recovered from high altitude weather balloons in the stratosphere, the layer above the troposphere, over 130,000 feet up! They contribute to a secret society of vagabond travelers known as aerial plankton.
There are even animals inhabiting the aerial ecosystem. In a 0.6 mile column of air, it’s estimated that there are 3 billion insects just drifting. Even spiders take their part in this whimsical form of travel, literally hanging from their silks 14,000 feet in the air.
Tons of viruses, bacteria, and fungi contribute to the biosphere way up there and even plants can spend parts of their life cycle as airborne spores. Although aerial plankton’s rogue, illusory nature makes them hard to study, specimens can be caught in nets attached to an aircraft or balloon.
Fittingly, aerial plankton are pretty famous! Check out NPR’s illustrious animation showcasing the arthropods of aeroplankton.
Science is a renewing process that constantly drives us to revise our knowledge, and challenge what we think we know through testing and evidence-based arguments.
On the surface, it might seems to be the antithesis of all things whimsical and imaginary. Until, of course, you look up at the sky and realize just how many invisible interactions allow it to be there.
Don’t take my word for it! View the full list of citations and additional resources here.
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Hi! I’m Bayleigh. When I’m not writing about my favorite microbes, you can find me enjoying stories (poems and prose), and admiring cyanobacteria.
