[audio:http://wamcradio.org/EarthWise/wp-content/uploads/2012/09/EW-09-18-12-Air-We-Breathe-.mp3|titles=EW 09-18-12 Air We Breathe]
We often hear the phrase “Have you thanked a green plant today?” That’s because plants provide nearly all of our food, fuel, and fiber. And during photosynthesis, plants give off oxygen to the atmosphere. Sometimes, we hear that the Amazon rainforests are the lungs of the Earth—taking up carbon dioxide and giving off oxygen to our atmosphere.
But, when it comes to atmospheric oxygen, we need to put the role of land plants in perspective. In any given year, all of the plants on land contribute around 0.01% to the mass of atmospheric oxygen—a trivial amount on all but the longest scale of geologic time. Moreover, decomposing plants in our forests consume an equivalent amount of oxygen.
So, where does the oxygen that makes up nearly 21% of our atmosphere come from? The answer lies largely in tiny marine plants called plankton, which gives off oxygen. Over eons of geologic time, marine plankton died, burying their organic matter at sea. Because they didn’t decompose, they didn’t use up atmospheric oxygen.
Some of this ancient marine matter has been transformed into the fossil fuels we use today. But, the majority is dispersed at low concentrations in sedimentary rocks.
If we burned all of the buried organic matter in the Earth’s crust, we would certainly make a dent in the concentration of oxygen in our atmosphere. But cutting and burning all the land plants on Earth today would have only a trivial impact on atmospheric oxygen.
We want to thank land plants for what they contribute to life on this planet. The list is long, but it does not include the day-to-day maintenance of the air we breathe.
Photo, taken on July 18, 2005, courtesy of Justin Ennis via Flickr.