In between Earth and space lies an ocean of air. That “great aerial ocean,” as biologist Alfred Russel Wallace (the other natural selection guy) called it, is an extremely thin envelope of gas and suspended particles that encompass our planet. To get perspective on just how thin, there’s this very rough equivalency: The atmosphere is to the Earth as an onion’s wafer thin outer skin is to an onion. But while it may be just a sliver, it’s critical to life on Earth.
Without our atmosphere, there wouldn’t be rain for our plants and vegetables to grow—and feed us. There’d be no greenhouse effect keeping the planet temperate enough to sustain life. There’d be no talking or music-playing because sound wouldn’t exist as we know it—without a medium like air, sound waves can’t travel and thus don’t create vibrations that hit our eardrums allowing us to hear. And there wouldn’t be the oxygen we need to breathe. Bottom line, without it, life on Earth would be nada.
|Scientists have identified five layers of the atmosphere each with different temperature and chemical distinctions. Click on the thumbnail above for a visual overview.|
Now, ours is not the only planet with an atmosphere, but none of those others is nearly as supportive and protective as Earth’s. Take Venus; its atmosphere is 96 percent carbon dioxide (CO2), about 90 times heavier than ours and “hot enough to burn lead.” Not what you’d call welcoming.
Our atmosphere, on the other hand, lays out the welcome mat.
First off, it circulates air, connecting the planet to everything living and breathing on it. The scientist Tim Flannery writes in his book The Weather Makers that the CO2 you breathe today may next week feed a plant on another continent—and that in a matter of months the CO2 you just breathed will be dispersed around the globe. (Gives one pause when thinking about pollution for sure.)
What’s more, the atmosphere is made up of roughly 21 percent oxygen, that element that humans gulp by the gallon—145 of them—into our lungs daily. Another 78 percent of Earth’s atmosphere is nitrogen, one of the building blocks of DNA. Argon comprises roughly 0.9 percent of the atmosphere, with the final 0.1 percent comprised of a mix of trace elements, which, while proportionally small, are very important. For example:
- Carbon dioxide accounts for fewer than four out of every 10,000 molecules, but they are key to making it warm enough for life here. (Too much C02 can, as we’re witnessing at present, detrimentally lead to an enhanced greenhouse effect aka global warming).
- Water vapor, another important trace element, is key to transporting energy, regulating temperatures, and creating weather.
- Stratospheric ozone protects the Earth from the sun’s harmful UV radiation; without it, there’d be more skin cancer, cataracts, and compromised immune systems.
But while all these elements swirl around the great oceanic atmosphere, the mix is far from uniform. In fact, 80 percent of all the atmosphere’s gases can be found in the troposphere alone, the region closest to Earth and the only breathable part of the atmosphere. Scientists have identified five layers of the atmosphere differentiated by chemical composition, density, and temperature. Below is an overview.
Image Credit: iStock.com/DeltaOFF
Derived from the Greek word tropos, which means “turning,” the troposphere is where the air mixes and turns. It extends from the Earth’s surface to roughly six miles above.* It’s where we live, and where a lot goes on.
Because most water vapor is in this layer, most clouds are found and most of our weather occurs here.
The temperature gradient here is inverted: Warm air is closer to the Earth and cooler air is higher up. (The reason for this is that when solar energy hits the Earth, the air directly above Earth’s surface warms, and cools the further away it goes.)
Some airplanes and most classes of drones fly in this area.
Only the lower part of the troposphere is breathable because there is less oxygen at increased altitudes (where atmospheric pressure drops). This is why mountain climbers attempting the summit of Mt. Everest tend to need extra oxygen.
Remarkably, the bar-headed goose can fly high (without training) to dizzying heights of 23,000 feet (~4.35 miles) where the air is only 10 percent oxygen.
Bumblebees are also impressive flyers in low-oxygen environments. While scientists don’t think they could quite fly as high as Mt. Everest, it is thought these bees can withstand the atmospheric pressure of 29,029 feet, and have been caught flying in the wild as high as 10,660 feet (~2 miles). But in simulated flights bees have flown as high as 500 feet above Mt. Everest.
Between each layer are “pauses” where “the maximum changes in thermal characteristics, chemical composition, movement, and density occur.”
Image Credit: iStock.com/milehightraveler
This layer, situated from approximately 6.2 to 8.1 miles above the Earth’s to about 31 miles above, is where the jet streams lie—those high-speed ribbons of air. Most commercial jets fly in this area, as do weather balloons (usually 11-23 miles high). The protective ozone layer is in this part of the atmosphere.
Image Credit: NASA
This layer extends from the stratopause to about 53 miles above Earth’s surface. The higher up in the mesosphere one goes, the colder it is. Most meteors occur here. Special high-altitude lightning, known as lightning sprites, have been spotted here. And a strange kind of cloud, called a noctilucent cloud and thought to be made of ice crystals or frozen water, forms here.
Image Credit: Wiki CC/Carsten
Extending from the mesopause to 430 miles above earth, this is where the space shuttle orbited. It’s also where those beautiful auroras occur—some 93 miles above Earth’s surface. A part of the thermosphere called the ionosphere allows radio communications.
Closest to space with a nebulous border that merges with space, the exosphere is not always recognized as its own layer. It’s in this area where most meteors occur between 50 and 75 miles above Earth. The International Space Station orbits in this layer and below.
One final thought. Our atmosphere wasn’t always as hospitable as it is now. It took billions of years for oxygen levels to rise enough to support oxygen-hungry animals like us. And as much as it supports us, we also influence it. In fact it’s clear that our interactions with this dynamic force can change—and have profoundly changed—it. People of a certain age may remember spray deodorants and refrigerants like Freon. Those items are no longer around because it turned out that the chlorofluorocarbons they contained destroyed parts of the ozone layer. Through the Montreal Protocol countries around the world came together to phase out such ozone-depleting substances, and years later the effort is paying off. But there are still issues with our atmosphere, including the amount of pollution we are putting into it and the amount of heat-trapping gases like CO2 and methane we’re adding to it. Seems like a smart idea to treat our atmosphere right.
*Near the equator and in summer the troposphere can reach as high as 10 miles. Near the poles and in winter, it can be as low as four miles.
Infographic by Julie Rossman.
By: Erica Rowell
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