Fellow Science Lovers,
Book update: I’ve published a short story! You can read A Cartoon Saves the Solar System in the Terrific Tomorrows anthology. Buy it here: https://www.amazon.com/dp/B0D915GBZZ
I’ve read the other stories in this book. All are clean and easy to read. Many are good, while a few are excellent. Recommended for ages 8 and up. I’ll also be selling signed copies of this at local events in a few weeks!
Electrons Are an Excitable Bunch
In Scribes’ Descent, we see mentions of underground people glowing. Their hair, irises, and skin–all presumably because they eat glowing plants. How would this work? In fact, how does any living creature emit light to begin with? To answer this, we have to look at electrons. Prepare yourself.
If you remember high school chemistry, (for me that was a LONG time ago), you may recall that atoms have a nucleus with electrons “orbiting” them. You may even remember that those electrons fill shells around the nucleus in a certain way:
- 1st shell holds up to 2 electrons
- 2nd shell holds up to 8 electrons
- 3rd shell holds up to 18 electrons
- 4th shell holds up to 32 electrons
- 5th shell holds up to 50 electrons
- 6th shell holds up to 72 electrons
Think of this like assigned seating. Here’s an example:
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-from Wikimedia by user GregRobson https://commons.wikimedia.org/wiki/File:Electron_shell_062_samarium.png
The first shell is the innermost one. In the image above, that would be the circle immediately surrounding the pink nucleus with “Sm” in the middle. It’s the one with only 2 electrons. I don’t know about you, but that’s romantic. Guys, the next time you see your wife or girlfriend, say that you and her are like the two electrons on the first electron shell. That you have front row seats for the nucleus and all your electronic fellows have to sit behind you.
That’s quantum love right there.
The second electron shell is the next one out, and it has 8 electrons, and so forth. The farther away from the center the shell is, the higher the energy those electrons have. Think of the first electron shell like a car parked in neutral on a small hill and the second electron shell like a car sitting on a taller hill, and so forth. The higher the hill, the more energy the car will have once it rolls down.
The act of pushing a car up a hill stores potential energy in the car. Pushing the car down the hill releases all that energy.
(Disclaimer: this is not a perfect analogy, but it gives you the gist of what’s happening here. Some electrons in the 3rd shell have more energy than other electrons sitting in that same shell. I’ll spare you the reason why, because it gets complicated.)
Why does this matter for light?
When you give enough energy to an electron, it will get “excited” and jump up to a higher energy level (a shell that’s farther out–usually.) Problem is, electrons are unstable up there, and they want to fall back down to the lowest energy level it can fit in. When this happens, the electron loses energy in the form of a photon, which is a tiny packet of light. Remember that light is an electromagnetic wave. If the amount of energy the electron loses causes the resulting photon to have a wave between 400 to 700 nanometers long, that photon will appear as visible light. And the length of the wave decides the color.
Why does fire create light?
Fire doesn’t just excite pyromaniacs, it also excites electrons. So are electrons pyromaniacs, then? Maybe. Anyhow… combustion gives lots of extra energy to electrons, sending them out to higher energy levels. They quickly fall back to their previous energy level and emit photons.
So then how don’t glowing plants and animals burn up?
Fire isn’t the only way to excite electrons. You can also:
- Shoot a photon at an electron
- Shoot other particles at an electron
- Put the electron in a strong enough electric field (this is how an LED works)
- Use a chemical reaction (this is what plants and animals use)
As it happens, using a chemical reaction to make light produces very little heat, so it’s safe for plants and animals. In general, this is called chemiluminescence. But when living things do it, we call it bioluminescence. Which brings us to the original question:
How does bioluminescence work?
Any time a chemical reaction releases more energy than it absorbs, we call it exothermic. Here are some common examples:
- Fire
- Rust
- Explosions
- Concrete setting
- Respiration
- Bioluminescence
Exothermic reactions usually happen when you form a chemical bond between two or more atoms. Doing this releases heat. How much? That depends on the reaction. Bioluminescence releases very little heat because of how efficiently its converts energy into light instead of heat (around 80% to 90%.) Compare this to manmade lighting: LEDs are 40% to 50% efficient and incandescent bulbs are a measly 10% to 20% efficient.
What decides whether a chemical reaction will release light or only heat?
You’re asking really good questions, and I couldn’t find a good answer for this one. Here’s what I did find:
Most plants and animals use a kind of chemical called luciferin. This word comes from the Latin lucifer, which means “light-bearer.” Yes, this is the same name that Satan used to have. No, the devil doesn’t make fireflies glow–he just makes BBQ sauce really hot. That’s what the bottles in my pantry claim, anyhow.
Now luciferin is not one chemical, but a whole class of them. And most organisms use a different luciferin. That means the chemical reaction happening inside a firefly is different from the one happening inside some freshwater snails. And the luciferin used by some sea creatures is different from both of those.
To keep things slightly less complicated, we’ll limit our discussion to how fireflies glow. Let’s start with a chart of boxes labeled with weird words:
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-from Wikimedia by user Jerine Victor https://commons.wikimedia.org/wiki/File:Bioluminescence_operation.jpg
Of course, this is a super-simplified chart. If you want to see the actual chemical structures of each of these, you can find them here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11115821/
Fair warning, these compounds are big and complicated. And for whatever reason, I couldn’t find a chemical formula or structure diagram for firefly luciferase (the enzyme). I must’ve searched 40 websites. Not sure if this is a secret or nobody knows it or my google-fu is broken. If any of you happen to know, PLEASE reply and let me in on this! My geeky heart is angsting over this.
From this chart, we see that fireflies don’t just do 1 chemical reaction, but at least 4 of them. And only 1 reaction produces light: the step where luciferal adenylate combines with oxygen gas to form light and oxyluciferin. Combining with oxygen is key. This is called oxidation, and this is the step that gives electrons the energy boost needed to jump into higher energy levels. When those electrons fall back down, that’s the bit that makes the bug’s butt glow!
Is this the only cause? Some articles say that luciferin absorbs UV light to excite its electrons. So which is it? The oxidation of luciferal adenylate or the absorption of UV? Or is it some of both? Scientists don’t know exactly how this works.
Let’s look at the inputs needed for these reactions:
1. Using special light cells, fireflies create both luciferin and luciferase in their bodies.
2. They take glucose from their food and metabolize that into ATP (adenosine triphosphate).
3. They breathe in O2 from the air.
4. They take in magnesium from their food. (this input isn’t shown in the chart)
Humans have the last 3 items covered. We’re pretty good at eating and breathing, not to brag or anything. Item 1 is where we fall short. People just don’t synthesize luciferin and luciferase. If you needed a life goal, now you have one!
So… why does this matter to the Scribeverse?
Because, in the Scribe Series, people living underground are glowing. Why? Because they eat glowing plants. So does eating those plants make them develop the same light cells that fireflies have? No. That would require dramatic DNA changes. Like CRISPR gene editing, which the Ground Dwellers don’t have the tech to pull off.
Then do the chemical inputs like luciferin and luciferase get transferred from the plants into the humans and then react inside of them? While possible, it’s unlikely to explain how even the Ground Dwellers’ hair glows. Even if the chemicals got into the bloodstream and circulated throughout the body, would that really transport the chemicals into their hair?
If neither of those are likely, how do these people glow?
Bioluminescent Bacteria
Many species of marine animals glow because of bioluminescent bacteria that live symbiotically in or on their bodies. The light at the end of an angler fish? That’s bacteria. And that dangling lure? That’s called an esca. How exactly do angler fish manage to collect Enterovibrio bacteria on their escas? We still don’t know, but it probably involves intimidation and an offer that can’t be refused. There’s a good reason I didn’t include a photo of this fish here. It’s FREAKY. If you really must, go google it for yourself, but don’t say I failed to warn you. And if you run into an anglerfish someday, don’t tell it I called it freaky.
So the Ground Dwellers are getting a similar bacteria from glowing plants found deep within the Bioprison. That bacteria can easily cover the skin and hair and even get into the eyes. Yes, the human eyes have their own microbiome.
If the answer was bacteria, why did I talk at length about how fireflies glow? Because all bioluminescence works in that same general way, just with slightly different chemical reactions. As long as the glowing bacteria have the chemical inputs it needs from plants or human hosts, it will gladly live there and let its little light shine. (You can’t hide your light under a bushel if you are the bushel!)
And, it has to be said: humans already glow. You read that right. We emit light in the visible spectrum, but it’s far too faint for the human eye to see (by a factor of 1,000). And we do this via bioluminescence. We have chemical reactions that produce heat and excite electrons. And our melanin has fluorescent chemicals, too–but all of this is on a very small scale. Phooey.
Wait, fluorescence? What’s that? I’ll save that for another newsletter.
So there it is, my fellow obligate aerobes. Now you know why the Ground Dwellers glow.
References:
https://www.nbcnews.com/id/wbna32090918
https://www.aao.org/eye-health/anatomy/microbiome-of-eye
https://ocean.si.edu/ocean-life/fish/meet-tiny-bacteria-give-anglerfishes-their-spooky-glow
Writing update: I have only 3 more chapters to write/rewrite for Scribes Emerge, Scribes Series book 3. Then I’ll post everything on Scribophile to get critiques before I do my next round of edits. In the meantime, check out my new short story in Terrific Tomorrows! That’s the only way you’ll find out how a cartoon could possibly save our solar system.
See you next month,
Dylan West
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