1 00:00:01,920 --> 00:00:06,560 Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey, 2 00:00:06,600 --> 00:00:11,680 Speaker 1: brain Stuff, Lauren vogelbamb here, you probably don't appreciate plants enough. 3 00:00:12,280 --> 00:00:15,480 Speaker 1: It's okay, none of us do. Given that plants have 4 00:00:15,560 --> 00:00:18,079 Speaker 1: been the major player in the convoluted soap opera of 5 00:00:18,120 --> 00:00:20,439 Speaker 1: life that landed us on this planet, we should be 6 00:00:20,480 --> 00:00:24,480 Speaker 1: thanking our leafy friends every day for our existence. Honestly, 7 00:00:24,640 --> 00:00:27,360 Speaker 1: the whole story is so tangled and complicated we may 8 00:00:27,440 --> 00:00:30,240 Speaker 1: never know the truth about how our mean green ancestors 9 00:00:30,240 --> 00:00:33,199 Speaker 1: allowed everyone else to evolve. But one aspect of the 10 00:00:33,240 --> 00:00:37,360 Speaker 1: story certainly involves photosynthesis of plants ability to make its 11 00:00:37,360 --> 00:00:41,920 Speaker 1: own food out of sunlight. We spoke with Gregory Schmidt, 12 00:00:42,040 --> 00:00:44,640 Speaker 1: Professor emeritus in the Department of Plant Biology at the 13 00:00:44,760 --> 00:00:48,559 Speaker 1: University of Georgia. He said a great way to appreciate 14 00:00:48,560 --> 00:00:51,559 Speaker 1: photosynthesis is to compare Earth's atmosphere with that of our 15 00:00:51,600 --> 00:00:55,280 Speaker 1: sister planets, Mars and Venus. All three planets were most 16 00:00:55,320 --> 00:00:58,560 Speaker 1: likely similar when they formed and cooled, but the atmospheres 17 00:00:58,600 --> 00:01:03,080 Speaker 1: of both Venus and Mars have carbon dioxide, two point 18 00:01:03,120 --> 00:01:06,760 Speaker 1: seven percent nitrogen and zero point one three percent oxygen. 19 00:01:07,520 --> 00:01:11,480 Speaker 1: Earth's air is seventy seven percent nitrogen, twenty one percent oxygen, 20 00:01:11,680 --> 00:01:15,000 Speaker 1: and zero point four one percent carbon dioxide, although that 21 00:01:15,080 --> 00:01:18,919 Speaker 1: number is rising. That means there are eight hundred gigatons 22 00:01:18,959 --> 00:01:22,200 Speaker 1: of carbon dioxide in our atmosphere, but there's another ten 23 00:01:22,240 --> 00:01:26,520 Speaker 1: thousand gigatons missing or buried in the form of fossil, limestone, coal, 24 00:01:26,800 --> 00:01:31,240 Speaker 1: and oil. In other words, carbon has been smuggled out 25 00:01:31,240 --> 00:01:34,160 Speaker 1: of the atmosphere and into Earth's crust for billions of years, 26 00:01:34,400 --> 00:01:36,480 Speaker 1: which is the only reason this planet is at all 27 00:01:36,560 --> 00:01:41,640 Speaker 1: habitable by multi celled organisms. Schmidt said, So, how did 28 00:01:41,640 --> 00:01:45,760 Speaker 1: that dramatic atmospheric shift happen for Earth? There's only one answer, 29 00:01:45,800 --> 00:01:49,320 Speaker 1: and it's pretty simple. Photosynthesis, the most amazing factor in 30 00:01:49,360 --> 00:01:54,880 Speaker 1: Earth's evolution. Yes, friends, photosynthesis. A couple hundred million years 31 00:01:54,920 --> 00:01:58,320 Speaker 1: after the Earth was formed, life showed up, probably first 32 00:01:58,320 --> 00:02:02,080 Speaker 1: as some anaerobic bacteria, that is, bacteria that can't thrive 33 00:02:02,160 --> 00:02:06,040 Speaker 1: in the presence of oxygen. These single celled organisms lived 34 00:02:06,040 --> 00:02:08,560 Speaker 1: by slurping up the sulfur and hydrogen that came out 35 00:02:08,560 --> 00:02:13,239 Speaker 1: of hydrothermal vents. Now we've got everything from butterflies to giraffes. 36 00:02:13,720 --> 00:02:16,160 Speaker 1: But there were a few steps on the road between 37 00:02:16,160 --> 00:02:20,160 Speaker 1: the first bacteria and giraffes. Those ancient bacteria had to 38 00:02:20,240 --> 00:02:23,440 Speaker 1: figure out a means of finding new hydrothermal vents, which 39 00:02:23,520 --> 00:02:26,360 Speaker 1: led to the development of a thermal sensing pigment called 40 00:02:26,360 --> 00:02:30,200 Speaker 1: bacterial chlorophyll, which some bacteria still used to detect the 41 00:02:30,280 --> 00:02:34,720 Speaker 1: infrared waves otherwise known as heat. These bacteria were the 42 00:02:34,760 --> 00:02:38,600 Speaker 1: progenitors of descendants that could make chlorophyll, a pigment that's 43 00:02:38,639 --> 00:02:41,520 Speaker 1: able to capture shorter, more energetic light waves from the 44 00:02:41,560 --> 00:02:44,840 Speaker 1: sun and use them as a source of power. So, 45 00:02:45,040 --> 00:02:48,240 Speaker 1: in essence, these bacteria created a means to capture the 46 00:02:48,400 --> 00:02:52,720 Speaker 1: energy of sunlight. The next evolutionary lead necessitated working out 47 00:02:52,760 --> 00:02:56,000 Speaker 1: a means of stable energy storage, creating a sort of 48 00:02:56,000 --> 00:02:59,720 Speaker 1: sunlight battery that encouraged protons to accumulate on one side 49 00:02:59,720 --> 00:03:03,440 Speaker 1: of their internal membranes versus the other. The true wonder 50 00:03:03,440 --> 00:03:06,280 Speaker 1: of plant and algae evolution is the fact that at 51 00:03:06,320 --> 00:03:11,400 Speaker 1: some point these ancient chlorophyll producing bacteria started generating oxygen. 52 00:03:12,080 --> 00:03:14,919 Speaker 1: After all, billions of years ago, there was actually very 53 00:03:14,919 --> 00:03:17,639 Speaker 1: little oxygen in the atmosphere, and it was toxic to 54 00:03:17,720 --> 00:03:20,680 Speaker 1: a lot of early bacteria. It's still toxic to existing 55 00:03:20,720 --> 00:03:23,800 Speaker 1: anaerobic bacteria that's still thrive in the oxygen free places 56 00:03:23,840 --> 00:03:27,840 Speaker 1: on Earth. However, the new process of capturing and storing 57 00:03:27,880 --> 00:03:33,720 Speaker 1: sunlight required the participating bacteria to burn water. The process 58 00:03:33,760 --> 00:03:37,119 Speaker 1: that we call burning or combustion is basically just very 59 00:03:37,320 --> 00:03:41,080 Speaker 1: rapid oxidation, the ripping off of electrons from one atom 60 00:03:41,280 --> 00:03:43,800 Speaker 1: and the transfer of those electrons to another, which is 61 00:03:43,800 --> 00:03:48,240 Speaker 1: called reduction. Early photosynthetic bacteria developed a way to capture 62 00:03:48,240 --> 00:03:51,120 Speaker 1: photons or particles of light, and use their energy to 63 00:03:51,200 --> 00:03:53,920 Speaker 1: strip water of many of its protons and electrons to 64 00:03:54,040 --> 00:03:58,680 Speaker 1: use for energy production. The breakthrough of breakthroughs that happened 65 00:03:58,720 --> 00:04:02,400 Speaker 1: three billion years ago was when photosynthetic machinery was perfected 66 00:04:02,400 --> 00:04:05,600 Speaker 1: to the point that chlorophyll could split two water molecules 67 00:04:05,640 --> 00:04:08,360 Speaker 1: at the same time. These days, we call this a 68 00:04:08,440 --> 00:04:15,640 Speaker 1: photosystem to chlorophyll protein cluster. Cyanobacteria evolved once these photosynthetic 69 00:04:15,640 --> 00:04:18,520 Speaker 1: bacteria figured out how to burn water and store the 70 00:04:18,600 --> 00:04:23,440 Speaker 1: energy from that chemical reaction in photosynthesis, photosystem to water 71 00:04:23,520 --> 00:04:27,680 Speaker 1: burning can't really be sustained without the second stage photosystem, one, 72 00:04:28,000 --> 00:04:30,560 Speaker 1: which involves taking the electrons swiped off of the water 73 00:04:30,640 --> 00:04:33,000 Speaker 1: molecules in the first step and making use of them 74 00:04:33,040 --> 00:04:37,000 Speaker 1: before they decay. Photosystem one does this by sticking these 75 00:04:37,040 --> 00:04:40,000 Speaker 1: electrons on a chemical assembly line, so the organism is 76 00:04:40,040 --> 00:04:42,840 Speaker 1: able to retain that hard earned energy, which is then 77 00:04:42,960 --> 00:04:45,880 Speaker 1: used to convert carbon dioxide into sugar for the bacteria 78 00:04:45,960 --> 00:04:50,160 Speaker 1: to use as food. Once photosystems one and two were 79 00:04:50,160 --> 00:04:54,520 Speaker 1: sorted out, cyanobacteria took over the oceans, and because oxygen 80 00:04:54,560 --> 00:04:57,720 Speaker 1: was their waste product, it became plentiful in Earth's atmosphere. 81 00:04:58,560 --> 00:05:01,920 Speaker 1: As a result, many bacteria became aerobic. That is, they 82 00:05:01,960 --> 00:05:05,280 Speaker 1: required oxygen for their metabolic processes, or at the very 83 00:05:05,360 --> 00:05:08,760 Speaker 1: least they could tolerate it. About a billion years later, 84 00:05:09,040 --> 00:05:14,560 Speaker 1: Protozoa evolved as anaerobes scarfing up aerobic bacterial prey. What 85 00:05:14,600 --> 00:05:17,919 Speaker 1: researchers think happened is this, at some point in at 86 00:05:18,000 --> 00:05:22,040 Speaker 1: least one of these oxygen intolerant organisms, the oxygen tolerant 87 00:05:22,080 --> 00:05:25,960 Speaker 1: bacteria they ate weren't completely digested, but stayed within the 88 00:05:26,000 --> 00:05:30,159 Speaker 1: cell and ended up helping the oxygen intolerant anaerobic organism 89 00:05:30,440 --> 00:05:35,080 Speaker 1: cope with an aerobic environment. These two organisms stuck together, 90 00:05:35,440 --> 00:05:38,839 Speaker 1: and eventually the prey organism evolved into a cell organelle 91 00:05:39,040 --> 00:05:44,440 Speaker 1: called mitochondria. A similar scenario occurred with cyanobacteria around one 92 00:05:44,480 --> 00:05:48,720 Speaker 1: billion years ago. In this case, an anaerobic bacteria probably 93 00:05:48,800 --> 00:05:52,440 Speaker 1: gobbled up a photosynthetic bacteria, which ended up setting up 94 00:05:52,440 --> 00:05:56,279 Speaker 1: shop inside its host, resulting in a small membrane bound 95 00:05:56,400 --> 00:06:01,480 Speaker 1: organelle common to all plants. The chloroplast as, algae and 96 00:06:01,560 --> 00:06:05,479 Speaker 1: multicellular plants evolved and benefited from plentiful carbon dioxide and 97 00:06:05,560 --> 00:06:09,520 Speaker 1: increasing oxygen in Earth's atmosphere. Chloroplasts became the place where 98 00:06:09,560 --> 00:06:13,560 Speaker 1: photosynthesis of photosystem one, two, and even more complicated stuff 99 00:06:13,640 --> 00:06:17,520 Speaker 1: went down in each cell. Just like mitochondria, they have 100 00:06:17,600 --> 00:06:20,960 Speaker 1: their own DNA and spend their time busily harvesting light 101 00:06:21,040 --> 00:06:24,400 Speaker 1: for the plant, creating the entire foundation for life on Earth. 102 00:06:29,560 --> 00:06:32,360 Speaker 1: Today's episode was written by Joceline Shields and produced by Tyler. 103 00:06:32,440 --> 00:06:35,000 Speaker 1: Playing brain Stuff is a production of I Heart Radio's 104 00:06:35,000 --> 00:06:36,919 Speaker 1: How Stuff Works. For more in this and lots of 105 00:06:36,920 --> 00:06:39,719 Speaker 1: other life sustaining topics, visit our home planet has Stuff 106 00:06:39,720 --> 00:06:42,560 Speaker 1: Works dot com, and for more podcasts from my heart Radio, 107 00:06:42,680 --> 00:06:45,040 Speaker 1: you can visit the iHeart Radio app, Apple Podcasts, or 108 00:06:45,080 --> 00:06:46,719 Speaker 1: wherever you listen to your favorite shows.