Why do we breathe oxygen and not nitrogen?
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00:00 One of the first mass extinctions on our planet
00:06 took place long before the dinosaurs.
00:10 Let's go back a couple of billion more years,
00:14 when the Earth's atmosphere
00:15 was completely devoid of oxygen,
00:18 and a clever group of bacteria
00:20 called cyanobacteria got creative.
00:24 They converted sunlight into energy
00:28 and released oxygen as a byproduct.
00:32 To be more specific,
00:33 they became photosynthetic.
00:37 Why was the introduction of oxygen so devastating?
00:41 Why do we humans breathe oxygen
00:43 and not nitrogen?
00:46 And can some animals survive without oxygen?
00:52 This is What If,
00:54 and here's what would happen
00:56 if humans didn't breathe oxygen.
01:01 It was called the Great Oxygenation Event,
01:05 and it began when cyanobacteria
01:07 started turning sunlight into sugar
01:10 and excreting oxygen as waste.
01:13 Yup, photosynthesis.
01:17 But why was this so devastating
01:19 to life on Earth?
01:22 Oxygen began building up in the air and water.
01:27 Millions of anaerobic microorganisms,
01:30 tiny organisms that don't need oxygen to live,
01:33 died when oxygen levels continued
01:36 to increase in the atmosphere.
01:38 This was the beginning of the end
01:40 for a huge portion of life on Earth.
01:44 The gases in our atmosphere
01:47 shape life on Earth.
01:48 78% nitrogen and 21% oxygen
01:53 is the magic proportion.
01:55 So why do we breathe oxygen
01:57 and not nitrogen?
02:00 There are a couple of things
02:01 we need to understand about nitrogen
02:04 before this makes sense.
02:06 Nitrogen tends to bind with nitrogen.
02:10 Think of it as an introvert.
02:11 It rarely interacts with other things.
02:15 It has a covalent triple bond,
02:18 meaning the two nitrogen atoms
02:20 are so tightly bound to each other,
02:22 it takes either a lightning rod
02:24 or certain nitrogen-fixing bacteria
02:26 in the environment to split them apart.
02:30 Compared to nitrogen,
02:32 oxygen is much more like an extrovert,
02:35 and it's very reactive,
02:37 which is why it's used in so many
02:39 biochemical processes that support life.
02:43 But can some animals
02:44 live without oxygen, though?
02:47 Until recently, we believed breathing oxygen
02:50 was essential for all animals to survive.
02:54 But researchers just discovered
02:56 the first animal that doesn't use oxygen
02:59 for breathing, and it's a game changer.
03:02 Hyneguia salmonecola.
03:05 An 8-mm white parasite
03:07 infecting the flesh of Chinook salmon
03:10 has no mitochondrial DNA.
03:12 Yet this is how organisms normally
03:15 use oxygen to produce energy.
03:18 The reason why this animal
03:20 lost its genes to breathe
03:22 is still unclear,
03:24 but it may get its energy
03:26 from its infected host.
03:28 So what would happen if humans
03:31 didn't breathe oxygen?
03:33 How might we have evolved?
03:36 Would we be similar to the salmon parasite,
03:38 relying on a host to survive?
03:41 Or would we live in an underwater
03:44 mythical kingdom like Atlantis
03:46 and never set foot on land?
03:49 Maybe we would become more like plants,
03:51 photosynthesizing sunlight
03:53 to produce needed energy.
03:56 But would we still be considered human
03:59 if this was the case?
04:01 Today, our respiratory system
04:03 is made up of organs that take in oxygen
04:06 and expel carbon dioxide.
04:09 It works in conjunction
04:10 with the circulatory system,
04:12 delivering oxygen-rich blood
04:14 to all the cells in the body.
04:16 The blood then collects CO2
04:19 and other waste to transport
04:20 back to the lungs,
04:21 where it gets pumped out
04:23 when we exhale.
04:25 Without oxygen,
04:26 our current respiratory system
04:28 would either need a complete overhaul
04:30 or would not exist at all.
04:33 The change would be so significant
04:36 that everything in the world
04:37 would be different.
04:39 We likely would not have anything
04:41 in common with this new,
04:42 altered state of being.
04:44 And not having 7.5 billion humans
04:47 emitting CO2 into our atmosphere,
04:50 the process of photosynthesis
04:52 and plant life
04:53 would probably look very different.
04:56 Without the use of oxygen,
04:58 you could even argue
04:59 about our very existence.
05:02 Would we even exist on the planet today?
05:04 If we did,
05:06 we would be like obligate anaerobes,
05:08 organisms intolerant of oxygen.
05:11 This means we wouldn't survive
05:13 unless we lived in a vacuum-like space
05:16 devoid of oxygen.
05:18 So we'd potentially need sealed spacesuits
05:21 to protect us from Earth's atmosphere.
05:25 But what about our appearance?
05:27 Would we have grown
05:28 to the size of humans today?
05:31 We would be much smaller,
05:33 more closely resembling
05:34 the size of those microorganisms,
05:37 needing to stick to larger hosts
05:38 for survival.
05:40 Hopefully, we would fall
05:41 under the facultative anaerobes category.
05:44 They can grow with or without free oxygen,
05:47 so we could easily live
05:48 in the presence of oxygen without harm.
05:52 Fortunately, we have thrived
05:54 because we have evolved
05:55 to rely on oxygen.
05:57 And not just any amount.
05:59 It's the exact right amount of oxygen
06:01 at 21%.
06:04 If there were even a whisper more
06:06 or a gasp less oxygen in our atmosphere,
06:10 we wouldn't be able to live.
06:12 We breathe this oxygen 10 times a minute.
06:16 And if we stopped,
06:17 our brain cells would die off.
06:20 After about 5 minutes without oxygen,
06:23 brain damage happens.
06:25 And if our brain continues
06:27 not to get oxygen,
06:28 it means certain death.
06:32 Everything we see on Earth
06:34 is due to the evolution
06:35 of photosynthesizing bacteria
06:38 that pumped more oxygen
06:39 into the atmosphere.
06:42 Not being able to take advantage
06:44 of this abundance of oxygen
06:46 would have limited us
06:47 from becoming the humans we are today.
06:50 Perhaps instead,
06:52 we would be hanging out
06:53 with our new friends,
06:54 the Heneguya saumonicola parasite,
06:57 all greedily clinging
06:59 to the flesh of Chinook salmon,
07:01 and all living underwater.
07:03 Well, maybe.
07:05 But that's a story for another WHAT IF.
07:10 [music]