Take a deep breath.
In that single intake of air, your lungs swelled with roughly 25 sextillion molecules, ranging from compounds produced days ago, to those formed billions of years in the past.
In fact, many of the molecules you're breathing were likely exhaled by members of ancient civilizations and innumerable humans since.
But what exactly are we all breathing?
Roughly 78% of Earth's atmosphere is composed of nitrogen generated by volcanic activity deep beneath the planet's crust.
The next major ingredient is oxygen, accounting for 21% of Earth's air.
While oxygen molecules have been around as long as Earth's oceans, oxygen gas didn't appear until ocean-dwelling microorganisms evolved to produce it.
Finally, 0.93% of our air is argon, a molecule formed from the radioactive decay of potassium in Earth's atmosphere, crust, and core.
Together, all these dry gases make up 99.93% of each breath you take.
Depending on when and where you are, the air may also contain some water vapor.
