The movements of underwater creatures can sometimes appear to be more labored than those of land lubbers. This is due to the fact that the water they are moving through is generally a thousand times more dense than air. However we’re constantly engulfed by a sea of sorts as well- our atmosphere. Except for during especially humid summer afternoons, it can be easy to forget that we are immersed in a bubble of gases. The incredible frailty of this situation deserves a moment of reflection. The collection of gases that sustain all life on Earth is held in place by the gravitational pull of our planet, a planet that spins through our solar system at 67,000 miles per hour while being bombarded by blasts of solar radiation. Yet with help from our planet’s magnetic fields, which shield it from solar winds, most of our atmosphere manages to cling on as we hurtle through space. This is pretty good for us Earthlings. The air surrounding Earth has far reaching impacts into every aspect of life, but how did it get there?
The air around our planet has no clear defined edge, however most scientists refer to a line 62 miles high off the surface as where outer space begins. This air weighs far less than the water on earth, coming in at a mere 5,000,000,000,000,000 tons. Our atmosphere first came into being during the creation of our planet, as lightweight gases were drawn in by the gravity of primitive Earth. These gases slowly built up and their weight began to press down onto the surface. This atmospheric pressure is key in keeping liquid water on the surface of Earth, as once atmospheric pressure drops too low water quickly boils away. Our barren neighbor Mars is a good example of this, as we have found evidence that water once flowed over its red surface. At some point Mars seems to have lost its atmosphere, and along with it any liquid surface water it might have had.
The composition of the Earth’s atmosphere changed over time due to the geological processes and organisms occurring at different periods. For example, the atmosphere in the Jurassic period had an estimated 5 times the amount of C02 compared to ours due largely to erupting volcanoes. The concentration of different elements in the atmosphere has far reaching effects on the organisms living on the planet since each organism requires a unique cocktail of elements in order to survive and thrive. The relationship goes both ways, however, as living creatures have also played a role in the composition of our atmosphere. Plants are a major influence on our current atmosphere as they pump oxygen into the air. This oxygen leads to rapid growth in animal populations, which then exude other gases into the atmosphere. Oxygen currently makes up about 21% of the air we breathe. The combination of geological processes and organisms has created the unique mix of gases all around us, however it will constantly change as new organisms arise and geology winds its course.
Besides containing the oxygen and other elements necessary to our existence, Earth’s atmosphere ensures our survival by reducing temperature extremes during the night and day, shielding us from harmful solar radiation, and warming the planet. Luckily the hole in the ozone layer is showing signs of repairing itself due to the reduced use of CFCs, the chemicals responsible for a buildup of ozone-destroying chlorine in the atmosphere. It’s still a good idea to keep an eye out for ways that you can prevent undesirables from entering the air. After all, we’re practically swimming in it.