Welcome to brain Stuff production of I Heart Radio. Hey, brain Stuff, Lauren vogelbamb here, you probably don't appreciate plants enough. It's okay, none of us do. Given that plants have been the major player in the convoluted soap opera of life that landed us on this planet, we should be thanking our leafy friends every day for our existence. Honestly, the whole story is so tangled and complicated we may never know the truth about how our mean green ancestors
allowed everyone else to evolve. But one aspect of the story certainly involves photosynthesis of plants ability to make its own food out of sunlight. We spoke with Gregory Schmidt, Professor emeritus in the Department of Plant Biology at the University of Georgia. He said a great way to appreciate photosynthesis is to compare Earth's atmosphere with that of our
sister planets, Mars and Venus. All three planets were most likely similar when they formed and cooled, but the atmospheres of both Venus and Mars have carbon dioxide, two point seven percent nitrogen and zero point one three percent oxygen. Earth's air is seventy seven percent nitrogen, twenty one percent oxygen, and zero point four one percent carbon dioxide, although that
number is rising. That means there are eight hundred gigatons of carbon dioxide in our atmosphere, but there's another ten thousand gigatons missing or buried in the form of fossil, limestone, coal, and oil. In other words, carbon has been smuggled out of the atmosphere and into Earth's crust for billions of years, which is the only reason this planet is at all habitable by multi celled organisms. Schmidt said, So, how did
that dramatic atmospheric shift happen for Earth? There's only one answer, and it's pretty simple. Photosynthesis, the most amazing factor in Earth's evolution. Yes, friends, photosynthesis. A couple hundred million years after the Earth was formed, life showed up, probably first as some anaerobic bacteria, that is, bacteria that can't thrive in the presence of oxygen. These single celled organisms lived by slurping up the sulfur and hydrogen that came out
of hydrothermal vents. Now we've got everything from butterflies to giraffes. But there were a few steps on the road between the first bacteria and giraffes. Those ancient bacteria had to figure out a means of finding new hydrothermal vents, which led to the development of a thermal sensing pigment called bacterial chlorophyll, which some bacteria still used to detect the
infrared waves otherwise known as heat. These bacteria were the progenitors of descendants that could make chlorophyll, a pigment that's able to capture shorter, more energetic light waves from the sun and use them as a source of power. So, in essence, these bacteria created a means to capture the energy of sunlight. The next evolutionary lead necessitated working out a means of stable energy storage, creating a sort of sunlight battery that encouraged protons to accumulate on one side
of their internal membranes versus the other. The true wonder of plant and algae evolution is the fact that at some point these ancient chlorophyll producing bacteria started generating oxygen. After all, billions of years ago, there was actually very little oxygen in the atmosphere, and it was toxic to a lot of early bacteria. It's still toxic to existing anaerobic bacteria that's still thrive in the oxygen free places on Earth. However, the new process of capturing and storing
sunlight required the participating bacteria to burn water. The process that we call burning or combustion is basically just very rapid oxidation, the ripping off of electrons from one atom and the transfer of those electrons to another, which is called reduction. Early photosynthetic bacteria developed a way to capture photons or particles of light, and use their energy to strip water of many of its protons and electrons to
use for energy production. The breakthrough of breakthroughs that happened three billion years ago was when photosynthetic machinery was perfected to the point that chlorophyll could split two water molecules at the same time. These days, we call this a
photosystem to chlorophyll protein cluster. Cyanobacteria evolved once these photosynthetic bacteria figured out how to burn water and store the energy from that chemical reaction in photosynthesis, photosystem to water burning can't really be sustained without the second stage photosystem, one, which involves taking the electrons swiped off of the water molecules in the first step and making use of them
before they decay. Photosystem one does this by sticking these electrons on a chemical assembly line, so the organism is able to retain that hard earned energy, which is then used to convert carbon dioxide into sugar for the bacteria to use as food. Once photosystems one and two were sorted out, cyanobacteria took over the oceans, and because oxygen was their waste product, it became plentiful in Earth's atmosphere.
As a result, many bacteria became aerobic. That is, they required oxygen for their metabolic processes, or at the very least they could tolerate it. About a billion years later,
Protozoa evolved as anaerobes scarfing up aerobic bacterial prey. What researchers think happened is this, at some point in at least one of these oxygen intolerant organisms, the oxygen tolerant bacteria they ate weren't completely digested, but stayed within the cell and ended up helping the oxygen intolerant anaerobic organism cope with an aerobic environment. These two organisms stuck together, and eventually the prey organism evolved into a cell organelle
called mitochondria. A similar scenario occurred with cyanobacteria around one billion years ago. In this case, an anaerobic bacteria probably gobbled up a photosynthetic bacteria, which ended up setting up shop inside its host, resulting in a small membrane bound organelle common to all plants. The chloroplast as, algae and multicellular plants evolved and benefited from plentiful carbon dioxide and
increasing oxygen in Earth's atmosphere. Chloroplasts became the place where photosynthesis of photosystem one, two, and even more complicated stuff went down in each cell. Just like mitochondria, they have their own DNA and spend their time busily harvesting light for the plant, creating the entire foundation for life on Earth. Today's episode was written by Joceline Shields and produced by Tyler. Playing brain Stuff is a production of I Heart Radio's
How Stuff Works. For more in this and lots of other life sustaining topics, visit our home planet has Stuff Works dot com, and for more podcasts from my heart Radio, you can visit the iHeart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.