It’s easy to think of the world’s forests as the planet’s “lungs.” Trees pump out oxygen—the same stuff we breathe in. The bigger the tree the more oxygen it releases. But most of our breathable air doesn’t come from land. It comes from the world’s oceans. And the most important oxygen producers are some of the tiniest organisms on Earth.
The air we breathe is 78 percent nitrogen and 21 percent oxygen. The rest is made up of much less common gases, including carbon dioxide. But it wasn’t always that way. Until 600 million years ago, Earth’s atmosphere had less than five percent oxygen. It was mainly a mix of nitrogen and carbon dioxide. Land plants didn’t exist until 470 million years ago. Trees weren’t responsible for the increase in oxygen. So where did it come from? The ocean.
Plants, algae, and cyanobacteria all create oxygen. They do this through photosynthesis. Using energy from sunlight, they turn carbon dioxide and water into sugar and oxygen. They use the sugars for food. Some oxygen is released into the atmosphere.
But oxygen is also used up. Most living cells use it to make energy in a process called cellular respiration. When organisms die, they decompose. Decomposition also uses oxygen. Most oxygen that’s produced gets used up by these two processes. (Used up means the atoms become part of a different molecule. The oxygen atoms are still around, just in a different form.)
Over millions of years, tiny single-celled algae and cyanobacteria pumped out oxygen. Much of it got used up in respiration or decomposition. But some of those dead organisms didn’t decompose. They sank deep into the ocean and settled on the bottom. That left a tiny bit of oxygen behind. Instead of being used up, it stayed in the air.
In this way, the oceans slowly built up the oxygen in our atmosphere. At the same time, they decreased the amount of carbon dioxide. (Remember that photosynthesis uses carbon dioxide.)
Today, the process continues. We now know that more than half the planet’s oxygen comes from the ocean. Not the entire ocean—just the top 200 meters (656 feet) or so. That’s about as far as sunlight can travel through water to power photosynthesis. In this photic zone we find all kinds of photosynthetic organisms.
Some algae, like kelp, grow in towering plant-like strands. Most algae exist as single cells that make up what we call phytoplankton. (Phyto means plant-like. Plankton are tiny organisms that float in the water.) Diatoms are single-celled algae that build glass-like houses. Scientists estimate that the oxygen in one of every five breaths we take comes from diatoms.
An even tinier organism plays a similarly large role. Prochlorococcus bacteria are so small about 20,000 of them fit in a single drop of seawater. They live in a wide swath of the world’s oceans. There are somewhere around 3 billion billion billion Prochlorococcus cells in all. Together, they produce 5 to 10 percent of the oxygen we breathe.
Although trees and forests are essential oxygen producers, they’re not the only ones. Next time you think about Earth’s “lungs,” picture the ocean.
CHECK OUT THIS GREAT VIDEO
What are Phytoplankton? They are known as primary producers of the ocean—the organisms that form the base of the food chain. WHOI explores the microscopic, single-celled organisms.
Denning, S. Amazon fires are destructive, but they aren’t depleting Earth’s oxygen supply. The Conversation. August 26, 2019. https://theconversation.com/amazon-fires-are-destructive-but-they-arent-depleting-earths-oxygen-supply-122369
Mann, D.G. Diatoms. Tree of Life Web Project. http://tolweb.org/Diatoms/21810. Accessed on December 1, 2020.
Morsink, K. With Every Breath You Take, Thank the Ocean. Smithsonian. https://ocean.si.edu/ocean-life/plankton/every-breath-you-take-thank-ocean Accessed on November 30, 2020.
NASA Earth Observatory. Oxygen Factories in the Southern Ocean. https://earthobservatory.nasa.gov/images/87465/oxygen-factories-in-the-southern-ocean. Accessed on November 30, 2020.
NOAA. How has the ocean made life on land possible? https://oceanexplorer.noaa.gov/facts/oceanproduction.html. Accessed on November 30, 2020.
NOAA. How much oxygen comes from the ocean? https://oceanservice.noaa.gov/facts/ocean-oxygen.html. Accessed on November 23, 2020.
Partensky, F., W.R. Hess, and D. Vaulot. Prochlorococcus, a marine photosynthetic prokaryote of global significance. Microbiology and Molecular Biology Reviews. Vol. 63. March 1999. https://mmbr.asm.org/content/63/1/106
Pennisi, E. Meet the obscure microbe that influences climate, ocean ecosystems, and perhaps even evolution. Science. March 9, 2017. https://www.sciencemag.org/news/2017/03/meet-obscure-microbe-influences-climate-ocean-ecosystems-and-perhaps-even-evolution
Riser, S.C. & K.S. Johnson. Net production of oxygen in the subtropical ocean. Nature, vol. 451. January 17, 2008. doi: 10.1038/nature06441.
The Physics Factbook. Diameter of a Human Hair. https://hypertextbook.com/facts/1999/BrianLey.shtml. Accessed on December 1, 2020.
WHOI. Phytoplankton. https://www.whoi.edu/know-your-ocean/ocean-topics/ocean-life/phytoplankton/. Accessed on November 23, 2020.
“We MUST respect this earth - it is all we have
Claudio Dametto - South Australia
“I will always Vote to Preserve Our World.
Liam McGregor - Western Australia
“A simple message that even a politician can understand
Felicity Crombach - Victoria
“Please show you care about our future generations!!
Phil Harmer - New South Wales
“Save our world , Life & health before profits.
Kerry Lillian - New South Wales
“Close down all coal mines and Do not mine gas . Make these Companies
Daniel Johnson - New South Wales
“We want carbon free energy!
Edan Clarke - New South Wales
“Feels good to be taking a voter action step
Beaver Hudson - New South Wales
“Great Initiative. Let’s Hold elected officials Accountable to their bosses, us!
John Paul Posada - New South Wales
“We need actions not words we need honest democratic govt We need a pm
Bob Pearce - South Australia
“Thank you for this great resource. I was feeling helpless. Even this small step
Silvia Anderson - Victoria
“If political parties continue receiving political donations, we will rarely have politicians working for
Dan Chicos - New South Wales
“I only vote for people who will take urgent action to restore a safe
Susie Burke - Victoria
“Current government is not representing the opinion of the majority of Australian to meet
Neil Price - Tasmania
“We are fighting to rescue our kids' future from those who seek to steal
Vanessa Norimi - Queensland
“No time to waste Now or Never My vote is for NOW
Rosalie White - Victoria
“I am only 9 but I already care
Ava Bell - New South Wales
“From New Lambton Uniting Church - Caring for our world is a moral imperative.
Niall McKay - New South Wales
“Our federal govt is an International climate Embarrassment - its about time they stepped
Oriana Tolo - Victoria
“Vote earth this time!
Sue Cooke - Queensland
“We are in one on the wealthiest countries in the world. we have the
rowan huxtable - New South Wales
“The climate Emergency is the public health opportunity and urgent priority of the 21st
Mike Forrester - Victoria
“If they want my vote they better act now
Barbara McNiff - New South Wales
“We need to act locally now for the earth. Our only home. Vote Earth
Anne Miller - New South Wales
“I often look at the places I've known all my life and see how
Jim Baird - New South Wales
“Strike one For people power!!! Democracy might prevail outside the current cronyism that faces
Lorraine Bridger - New South Wales
“Our federal politicians Are Afraid to make action on climate change a major election
Jennifer Martin - New South Wales
“climate election, let's go!
Fahimah Badrulhisham - New South Wales
“Great to see this website that is a focus on action for climate change
Lynette Sinclair - New South Wales
“Let’s show politicians and the Murdoch media that climate change is by far the
Jane Aitken - Australian Capital Territory
“If you want to stay in power You need to take action to stop
Jane Bulter - New South Wales
“We are all that stands between terminal climate change and the vulnerable. We are
Carol Khan - Queensland
“We need a Government that Believes this is real and not taking money from
Ken Gray - New South Wales
“I'm voting for my childrens future
Anneliese Alexander - New South Wales