The History of Air
Paleontologists are looking to the fossil record to decipher what the earth's atmosphere was like hundreds of millions of years ago

The earth’s atmosphere is made up of a lot of nitrogen (78 percent), a bit of oxygen (21 percent), a splash of argon (0.93 percent), a small amount of carbon dioxide (0.038 percent) and trace amounts of other gases. But it has not always been so. The composition of gases in the atmosphere can change (and is changing now as we burn fossil fuels), and the fossil record reveals how something as deceptively simple as air can influence the history of life.

If you visited what is now North America 300 million years ago, near the close of the Carboniferous period, you would have been greeted by a very unfamiliar scene. The landscape was dominated by vast swamps filled with huge lycopods (relatives of club mosses that grew to the size of trees), amphibious vertebrates up to nearly 20 feet in length and enormous arthropods. The Meganeura, a relative of the dragonfly that had a wingspan more than two feet across, buzzed through the air over the giant Arthropleura, a nine-foot-long millipede. Never before or since have terrestrial invertebrates grown to such prodigious sizes.

Read the rest on the Smithsonian website.