Learn why carbon is the foundation of all life on Earth as we investigate a chemist’s suicide, death by air pollution, and one very, very cold murder case.
Featured above: Stanley Miller photographed next to a replica of his famous experiment he conducted alongside Harold Urey.
Bonds, Covalent Bonds: As promised, here’s a video from FuseSchool that does a pretty good job explaining covalent bonding, doesn’t get caught up explaining other types of bonds, and has some helpful visualizations.
It also mentions the Octet Rule, which can be helpful, but it’s not really a “rule” since not all elements abide by it. I didn’t want to confuse the issue by mentioning it in this episode, but if you just keep in mind that the Octet Rule only applies to the first twenty elements, for the most part, you’ll be fine.
Sadly, this video doesn’t include carbon as an example. Carbon, with six total electrons, including four in its valence shell, needs four more electrons to fulfill the Octet Rule.
Carbon actually can’t acquire those four electrons by bonding with a single other atom, so I can see why FuseSchool didn’t use carbon as an example here! (It can get those electrons by bonding with *two* [or more] other atoms, including two other carbon atoms. This is one reason why the element has a propensity to form long chains.)
The Great Pea Souper: Above, London’s Tower Bridge during the Great Smog of 1952.
io9 has a great collection of photos of smoggy London from various times in the 20th century, including the Great Smog of 1952. It’s hard to imagine living under those conditions 24 hours a day. Particularly telling is the photograph of an air filter after one night’s use.
We Didn’t Start The Fire: Centralia, PA is a coal town — or was. Now it’s a ghost town, thanks to a fire that’s been burning underground for more than half a century. Vsauce3 produced a bite-sized documentary that shows the effects of burning coal in a microcosm.
Whatcha Gonna Do With All That Trunk: Trees are among the largest living organisms on Earth, but we don’t often think about where they acquire the matter that gets converted into “tree.” The superb YouTube channel Veritasium takes a look at some common misconceptions in this short video:
A series of airtight glass tubes connected flasks of bubbling liquids, swirling clouds of vapor, and electric arcs of bottled lightning. If the experiment looked like a a movie set, the premise sounds like Frankenstein: Stanley Miller and Harold Urey were attempting to produce the chemistry of life from lifeless matter.
But this was science, not fiction. Miller and Urey had modeled the environment of early Earth. It was a simple model, but accurate. One flask of water was heated by a low flame, simulating the ocean and evaporation. The resulting vapor mixed with ammonia, methane, and hydrogen, gases that were all present on early earth. These were stimulated by a continuous electrical spark — much as they would have been in a primordial thunderstorm. Eventually the mixture cooled to liquid form, like rain, and returned to the first flask to undergo the cycle again. That was the entire experiment: Four very simple chemicals, a little heat, and electricity.
It started producing results almost immediately. After one day, the fluid turned a light pink color, and by the end of a week, several chemicals that are necessary components of life had formed. These chemicals are called amino acids, and they perform countless essential functions for life. Sometimes they combine to form various kinds of proteins. It’s no exaggeration to say that all life on earth is built out of amino acids. Miller and Urey had successfully shown that, even using a much smaller chemical palette than was actually present on early earth, these amino acids formed easily and spontaneously.
No experiment has actually created any new form of life, including this one. But that makes sense. Miller and Urey only ran their experiment for a week. Life on Earth has been in the making for over four billion years.
You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each week, we take a look at the fascinating true stories behind one element on the periodic table.
Today, we’re keeping things lively with carbon.
Life as we know it requires amino and nucleic acids, and in turn, those essential molecules all require carbon. In the Miller-Urey experiment, that carbon was supplied in the form of methane, CH4. Carbon isn’t even in the top ten most abundant elements on the surface of the earth, but it’s omnipresent in our lives, from the wood that frames our homes to the fuels that generate our electricity — not to mention the carbon throughout our bodies.1
But why is carbon the linchpin of life, rather than any other atom? Or several other atoms?
It’s because the chemistry of life is highly complex, and requires millions of different molecules that can perform highly specific functions. This kind of flexibility is where carbon excels. Particularly at the temperatures found on Earth, carbon can bond with many elements, including itself, to form rings, lattices, and long chains, each one different than the last. Carbon can form so many millions of molecular combinations that it’s one of the few elements with its own discipline of study, called organic chemistry.2
Carbon is so versatile because of its small size and four valence electrons. Like many elements, carbon has room for eight electrons in its outermost shell. Being half-full, it doesn’t react violently to acquire those extra four electrons — but it’s also not very picky about where it gets them from.3
There are several different ways that atoms bond together, but today we’ll focus on covalent bonds, since that’s carbon’s preferred method of grouping up.
Remember how a hydrogen atom has one valence electron, and wants to fill its shell with one more? Electrons generally don’t exist on their own, so it needs to grab one from another atom. Say another hydrogen atom comes along, and also wants to fill its shell with one more electron. In this case, Hydrogen 1 and Hydrogen 2 will each share their single electron with the other one, which is enough to satisfy them. The two atoms are sharing electrons in their valence shell, so their bond is covalent.
This kind of thing can be easier to grasp with visuals, so I’ll include a video that illustrates covalent bonding at episodic table dot com slash carbon.
The idea of atoms sharing electrons like this was first proposed in 1916 by Gilbert Lewis, an intellectual titan whose genius may have only been outmatched by his ego.
There is no denying he was an incredible scientist. He altered the landscape of chemistry in ways that have stood the test of time. In addition to discovering covalent bonds, he also came up with a standard notation to signify their particular arrangement. It’s called Lewis Dot Notation, and is still used today. He also discovered what acids and bases are, synthesized the first pure sample of heavy water, coined the word “photon,” and much more.4
The problem was, he knew how smart he was, and he didn’t think as highly of his contemporaries. He could be vicious in scientific papers, pointing out the pettiest of errors and serving backhanded compliments like, “Some arithmetic and thermodynamic inaccuracy occasionally marring their work is far outweighed by brilliancy of imagination and originality of experimentation.”
But Lewis’s rivals weren’t as stupid as he took them to be. Several of them ended up as voting members of Nobel Prize committees — one man held such a position for forty-two years. Having enemies in high places is probably why Lewis didn’t win the Nobel Prize he was nominated for in 1922… or in 1924… or any of the forty-one times he was nominated.5 No one in history has been nominated for as many Nobel Prizes as Lewis, but never once did he actually win.
Several of his students did go on to win those and other prestigious awards, including Harold Urey. But rather than being a proud teacher, this seems to have only made Lewis more bitter.
The last straw came on March 23, 1946. One of Lewis’s many rivals, Irving Langmuir, was receiving an honorary degree at the University of California – Berkeley, where Lewis worked and had spent most of his career. The two met for lunch, and there’s no record of what they happened to discuss. But according to Lewis’s colleagues, he was in a very foul mood when he returned. He sat down to play a game of bridge, but turned out to be in no mood for fun and games, so he returned to his work in the lab.
An hour later, a graduate student walked in and found Gilbert Lewis’s lifeless body on the floor. A shattered ampule of hydrogen cyanide laid nearby.
The coroner officially ruled it death by coronary artery disease, but he also didn’t investigate very rigorously. In a 1987 book, UC Berkeley Professor Emeritus William Jolly wrote,
In a retrospective symposium honoring G. N. Lewis, Michael Kasha attempted to quash the suggestion that Lewis committed suicide, but his arguments were not compelling.”
Curiously, scientific historians have noted that this seems to be a rather macabre tendency among the pioneers of statistical mechanics, a group that includes Lewis.6 At least ten such prominent chemists attempted to or did take their own lives.7 Physicist David Goodstein noted this in the opening of his books, States of Matter, in 1975:
Ludwig Boltzmann, who spent much of his life studying statistical mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study statistical mechanics. Perhaps it will be wise to approach the subject cautiously.”
Lewis illuminated the field of chemistry throughout his life, but we may never know for certain whether his death was intentional or accidental. We’ll move on to meet a man who is the exact opposite: we know very little about his life, but the mystery of his death has been almost completely solved.
On September 19, 1991, Erika and Helmut Simon were enjoying the last day of their vacation, hiking through the Otzal region of the Alps. They wandered off the marked trail a bit to try a shortcut through a gully when an unusual outcropping caught Helmut’s eye. Upon close investigation, they found that they had stumbled upon a human body, half of it still locked in glacial ice. The Simons realized that it was probably an unfortunate skier or hiker like them who had tumbled into the ravine last year. They used the last frame on their last roll of film to take a photo, then returned to a hiker’s shelter to report their discovery.8 9
This was morbid, but not entirely unusual. Austrian authorities had already recovered eight bodies that summer, and Italian authorities weren’t interested in investigating at all.
The Austrians arrived the next day by helicopter and got to work, using a pneumatic jackhammer and ice axes to carve the body out of the ice. These are’t the most precise tools in the world, and the body suffered a little for it: Parts of his clothes were shredded, and his hip was ruptured, exposing bone. Oops.
It took several days to finally free the body from its icy tomb, but when they did, medical examiners quickly realized that this man hadn’t died in the past year, or even the past decade. The question was, just how long ago had he died?
Only carbon could say.
A carbon atom is usually made of six protons, six neutrons, and six electrons. We know by now that the number of protons in an atom’s nucleus is what determines which element it is. Carbon can’t gain or lose protons without turning into something else, like when lithium turned into helium in episode three.
We have seen that atoms can exchange electrons with their neighbors — and often do. But we haven’t said much about the neutrons, those particles that pad the space between protons in the nucleus.
Carbon, and most other atoms, can gain or lose neutrons and retain its identity. But it can’t just gain or lose neutrons willy-nilly. They might have no electrical charge, but remember: Those neutrons play an important role in holding things together. An atom with too few neutrons will fly apart, and an atom with too many will become kind of wobbly, shedding particles until it’s stable again.
So a carbon atom with a different number of neutrons is still carbon, and this doesn’t have any effect on electrons, but clearly there’s some kind of effect. So scientists add up all the particles in an atom’s nucleus, and that denotes the atom’s variety. This is called an “isotope,” from two Greek word roots meaning, “same place” — as in, the same place on the periodic table. The most common isotope of carbon, with six protons plus six neutrons, is the isotope called carbon-12.
Two other carbon isotopes fit in that sweet spot of stability: carbon-13 and carbon-14, with seven and eight neutrons, respectively. Carbon-13 is actually quite stable, but not very common in nature. Carbon-14, on the other hand, is a little too heavy. It’s not violent, but over time, it will rearrange itself into a much more stable atom of nitrogen. Technically, that rearrangement is a type of radioactive decay.
One of the little miracles of our universe is that this radioactive decay happens at a perfectly consistent pace, depending on which isotope of which element we’re talking about. If you had a sample of carbon-14, after 5,700 years, exactly half of it would decay into nitrogen. The amount of time it takes for half of a sample to decay into something else is what’s called the isotope’s “half-life.”
It doesn’t matter how much carbon-14 you start with. If you have 100 atoms of carbon-14, in 5,700 years, you’ll have 50. If you have two kilograms of carbon-14, in 5,700 years, one kilogram of it will have turned into nitrogen and floated away. After 5,700 more years, you’ll be left with half a kilogram of carbon-14. This decay happens at such a reliable pace that you could set your watch by it. And that is just what scientists do when they want to determine the age of something that used to be alive.
As mentioned earlier, all life on earth is built on a foundation of carbon. Animals, plants, fungi, and microbes all consume carbon in some form or another — but none of them is very picky about which isotope of carbon they ingest. Roughly 99% of the carbon in an organism’s body is carbon-12, and just under 1% is carbon-13. An extremely small amount will consist of carbon-14. An organism will coincidentally consume carbon-14 at about the same rate that it decays into nitrogen, so these proportions stay roughly the same throughout the organism’s life.
However, as you may be aware, when something dies, it stops breathing, growing, eating, and, well, anything else. Since it’s no longer ingesting anything, the amount of carbon-14 in its body decays without being replenished. By checking the ratio of carbon-12 to carbon-14, scientists can accurately deduce how long ago the organism died.
That was precisely the test that revealed the surprising age of the frozen stiff. This was no unfortunate backpacker. It wasn’t even, as is sometimes found in the Alps, a fallen soldier from World War I.10 Carbon dating revealed that this man died well over five thousand years ago.
It was an overnight scientific sensation. Suddenly, people were acting far more careful than they had been at the excavation site. Because the man’s body was found in the Otzal region of the Alps, he became known as Otzi the Iceman. And Otzi had a lot to say about a very interesting time in human history.
Otzi died around 3200 BCE, which is after human civilization developed agriculture and started living in cities, but just before the invention of writing. He lived his life on the boundary between history and prehistory.
Considering his age, Otzi and his possessions were remarkably well preserved. His may be the single most studied body in history, since incredibly, scientists are still learning from Otzi over 25 years after his discovery.
Examiners discovered that he was around 45 years old when he died, standing 5 foot 5 with a slight build. He had a lot of health problems, including arthritis, gallstones, hardened arteries, and Lyme disease. As if that weren’t enough, he was carrying parasites capable of causing considerable gastrointestinal distress.
It wasn’t all health problems, though. His last meal still remained in his stomach — some unleavened bread, a few greens, and wild goat meat.11 Analysis of his teeth and bones pinpointed with impressive detail the valley where he spent his childhood, as well as the valley he moved to when he was an adult. Even Otzi’s hair told some of his story: High levels of copper and arsenic suggested that he spent much of his time smelting. Perhaps not coincidentally, among his belongings was an axe made of 99.7% pure copper.
There were other telling artifacts around the site, as well. Otzi had been well outfitted in a deer hide coat, and bearskin shoes of such high quality that some experts figure that shoe cobblers have been around for much longer than we thought.12 He carried special herbs known for their pain-killing properties — which makes a lot of sense, considering his health problems. Otzi was also carrying some half-finished arrows, along with a piece of yew he might have intended to fashion a bow out of.
But he never got the chance to finish those DIY projects. An early hypothesis was that Otzi had gone for a hike, perhaps gotten a bit lost, and died of exposure. But later evidence suggests that his bow and arrows were for something more than hunting game.
In 2001, ten years after Otzi was discovered, one researcher stumbled upon a massive clue that everyone else had somehow overlooked: An arrowhead, lodged deep in his left shoulder. Suddenly, the idea that this was a frail old man who got lost in the mountains sounded a little naive.
A frenzy of further study led to exciting new discoveries. DNA analysis showed that someone else’s blood stained the blade of his dagger; similar inspection suggested that Otzi had killed one man with an arrow, retrieved his ammunition, then killed a second enemy before fetching his arrow again. Another man’s blood on Otzi’s coat led scientists to theorize that he carried a wounded comrade over his shoulder.13
So sure, maybe he had a lot of health problems — some of them downright embarrassing — but this makes Otzi sound more like Mr. T than Tiny Tim.
Of course, unlike an action movie hero, Otzi clearly did not win the day. At some point, that arrow pierced his shoulder and caused massive bleeding. This slowed him down enough to allow his pursuer to land a final, crushing blow to Otzi’s head. There he fell, and there he remained. Over many weeks or months, snow fell and covered his body, freezing him in ice and in time until that fateful day in 1991.
As one of the oldest and most intact preserved bodies ever discovered, scientists haven’t just learned a lot about this one man who lived so long ago. He’s illuminated remarkable developments in human migration, the agricultural revolution, Neolithic European society, and much more. His discovery is one of the crown jewels of anthropological discovery.
Otzi’s age and his fine copper axe suggest that he played an important role in his society. If only he could have known how important he is to ours.
Since most living things don’t drop dead in a freezer, they tend to decompose much more quickly than Otzi did. Left alone for long enough, subject to the great pressure and heat beneath the Earth’s surface, the abundant carbon of their bodies sometimes consolidates into a rich, dense form like coal or crude oil.
As you probably know, these happen to burn extremely well, and so they’re often called fossil fuels. Sometimes people joke that we’re burning dinosaur bones to fuel our cars, and while this is technically kind of true, fossil fuels are mostly made of dead plants. It’s mostly a numbers game: For every pound of animal mass on Earth, there are a thousand pounds of plant material.14
Now, plants do a pretty decent job of burning on their own, as anyone who’s ever seen a fireplace or campfire knows. But coal, in particular, has plenty of advantages over wood as a fuel: It doesn’t need to be split or chopped; it’s not ruined by rain; and it can burn for far longer than wood.15
So when London suffered a wood shortage in the early 13th century, it’s understandable why the locals turned to coal to heat their homes and fire their kilns. They didn’t even need to go mining — the stuff was literally washing up on the beaches for easy collection.16
That’s very convenient and all, but there are problems with burning coal, too. It’s more difficult to start a coal fire, requiring a lot of time and kindling. Building a coal fire is a dirty affair, covering a person in black soot. And then, of course, there’s the thick, billowing smoke and nauseating smell — a stark difference from the pleasant scent of a wood-burning fire.
This was kind of a big deal. London and other large cities were particularly affected by wood shortages — and needed to burn a lot of coal to stay warm. When Queen Eleanor made a visit to the city of Nottingham in 1257, she was quickly driven away from the city by the intolerable fumes of burning coal.17
Those fumes aren’t merely unpleasant to smell, of course. Burning coal causes terrible health issues, from asthma and bronchitis to cancer and heart failure. 18 By 1307, the situation got so bad that King Edward I issued a Royal Proclamation that read in part:
An intolerable smell diffuses itself throughout the neighboring places, and the air is greatly infected, to the annoyance of the magnates, citizens, and others there dwelling and to the injury of their bodily health.”
The punishment for disregard was “great fines and ransoms,” but that wasn’t enough. Coal was cheap, but more importantly, it was available. In medieval England, “alternative energy” consisted of peat, which is dead plants that haven’t quite become coal yet, and animal dung. Wind and water power did technically exist at the time, but their kinetic energy couldn’t be converted to heat until the invention of electricity.
So coal didn’t go anywhere. Meanwhile, London’s population quadrupled from 1500 to 1600, so the problem became much worse. In 1661, a pamphleteer named John Evelyn published Fumifugium, one of history’s first treatises on air pollution. He wrote,
That hellish and dismal cloud of sea coal [means] that the inhabitants breathe nothing but an impure and thick mist, accompanied by a fuliginous and filthy vapour, which renders them obnoxious to a thousand inconveniences, corrupting the lungs and disordering the entire habit of their bodies, so that cattarrhs, phthisicks, coughs and consumption rage more in that one City than the whole Earth besides… Is there under Heaven such coughing and snuffling to be heard as in the London churches where the barking and spitting is incessant and importunate?”19
And then, after all that, London became ground zero for the Industrial Revolution.
Now coal wasn’t just warming homes and firing blacksmiths’ forges. It was the power behind the fastest growing industries in a city whose population had quadrupled once again since 1600. Ignoring the pollution didn’t make it go away, and it was starting to become a serious problem. On top of the smell and the sickness, there were days when the sun was entirely blacked out. At least twice during the 19th century, the smog got so bad that people dropped dead.
But that poisoned air was still making people rich. It wasn’t until 1952 that Londoners finally had to reckon with their denial.
December 5 was a particularly cold and foggy morning, so people were burning even more coal than usual. The damp air did an excellent job of holding soot in the air, compounding the problem further. These were typical circumstances. The unlucky part was the high-pressure weather system surrounding the city, which kept the stale and noxious cloud parked over London for five solid days.20
They were terrible days. There was no escape as the smog slowly seeped into people’s homes and offices. Visibility was practically nil, rendering driving and air travel impossible. Movie theaters and concert halls had to cancel their shows because audiences couldn’t see the stage. Two trains collided near London Bridge before all public transportation was canceled.
Sulfur dioxide from burning coal mixed with the damp fog to saturate the air with sulfuric acid, a chemical that can dissolve iron, let alone a pair of lungs. Between that, the carbon monoxide, and the thick smoke and dust lingering in the air, many people suffocated in their sleep. At least four thousand Londoners perished by December 10, with 150,000 hospitalized.21 Eight thousand more died from complications over the following months.23
This thick black cloud does have a faint silver lining: Four years later, parliament passed the Clean Air Act of 1956, which took several approaches to reducing air pollution across the United Kingdom. It wasn’t a perfect law, and London’s air quality is still pretty bad,24 but there hasn’t been an air pollution event so deadly since The Great Smog of 1952.
For seven and a half centuries, Londoners knew that burning coal emitted a odious smell that was bad for their lungs, bad for their skies, and bad for their sanity. But it was good for the economy, and was frequently the only fuel available.
Surely if they knew just how bad it was for themselves and their environment, and if they had some kind of alternative energy source, they would have stopped burning coal as quickly as possible.
Carbon is very easy to add to your collection. Quick — grab on to something that’s in arm’s reach. Chances are decent that whatever’s in your hand has some carbon in it. So this week, I would encourage everyone to become at least a little discerning with their collection.
See, pure carbon isn’t just common — it comes in several different varieties. Because of its characteristic flexibility, carbon atoms can bond with other carbon atoms in different ways. These varieties are called “allotropes,” which comes from two Greek word roots meaning, “different way.”
Sometimes carbon atoms just come together in one big mish-mosh, with no organization or order — like a messy sock drawer. This is called “amorphous” carbon, and coal is one such example.
You can still find sea coal on beaches occasionally after a storm. It happens to be a particularly beautiful kind of coal, often polished to a shine by the ocean waves. Of course, you could be old-fashioned and gather it from a mine, but that’s probably the least convenient way to acquire a sample of carbon for your collection. If you ask nicely, and you’re a really good chemist all year long, Santa Claus might leave a lump of coal under your Christmas tree.
Another of carbon’s allotropes can be found inside any pencil: Graphite. This is carbon that’s organized into sheets that are only one atom thick, layered on top of each other like a ream of paper. Each of these single layers is called graphene, and since 2004, scientists have been able to produce them in isolation. Graphene has some remarkable properties that graphite does not: It’s an efficient conductor of heat and electricity, but more notably, it’s the strongest material known to humanity — 200 times stronger than steel.
When a sheet of graphene is rolled into a cylinder, it’s known as a carbon nanotube. Once manufacturers figure out a cheap and efficient way to make the stuff, it’s likely to cause a revolution in industries of all kinds, from medicine and nanomachinery to sports gear and electronics.
Carbon is so versatile that materials scientists keep finding interesting new allotropes of carbon. One of them, when mapped out using a ball-and-stick model, happens to look exactly like a regulation soccer ball. It’s called “buckminsterfullerene,” after Buckminster Fuller, a man who did a lot of popular work with similar shapes. More casually, they’re referred to as “buckyballs.”25
It appears that some of the most exciting machinery of the future will be built on skeletons made of carbon. But there is one particular allotrope of carbon that’s been attracting discerning collectors since antiquity: The diamond. Carbon atoms arranged in a perfectly ordered cubic crystal to form a beautiful stone that’s surprisingly common around the world. If you really want your collection of the elements to stand apart from anyone else’s, spending thousands of dollars on a gleaming, vastly overpriced gemstone is one way to do it.
Thanks for listening to The Episodic Table of Elements. Next time, we’ll try not to choke on nitrogen.
Music is by Kai Engel. To learn about the Pennsylvania town that’s been on fire for sixty years, see photos of The Great Smog of 1952, and find out just where trees get their mass from, visit episodic table dot com slash carbon.
This is T. R. Appleton, reminding you that this is what happens when you find a stranger in the Alps.
- Nature, The Four Worlds Of Carbon. Simon H. Friedman.
- CK12.org, Significance Of Carbon.
- JRank, Why Carbon Is Special.
- World of Chemicals, Gilbert Newton Lewis – Discoverer Of Covalent Bond.
- Cathedrals of Science: The Personalities And Rivalries that Made Modern Chemistry. Patrick Coffey, 2008.
- Chemical Heritage Foundation, Gilbert Newton Lewis. Last updated July 23, 2015.
- An Encyclopedia Of Human Thermodynamics, Founders Of Thermodynamics And Suicide.
- Wired, Sept. 19, 1991: Hikers Stumble Upon Otzi, The Alpine Iceman. Tony Long, September 19, 2007.
- ThoughtCo., Otzi the Iceman: One Of The Greatest Archaeological Discoveries Of The 20th Century. Jennifer Rosenberg, November 13, 2017.
- The Telegraph, Melting Glaciers In Northern Italy Reveal Corpses Of WWI Soldiers. Laura Spinney, January 13, 2014.
- National Geographic News, Iceman’s Stomach Sampled — Filled With Goat Meat. Ker Than, June 23, 2011.
- The Telegraph, Now You Can Walk In The Footsteps Of 5,000-Year-Old Iceman — Wearing His Boots. Katka Krosnar, July 17, 2005.
- Mummy Tombs, DNA Tests Suggest Otzi Died After Fight But Not Alone. August 10, 2003.
- BBC, Which Form Of Life Dominates Earth? Nic Fleming, February 10, 2015.
- The Christian Science Monitor, Weighing The Options Of Coal Vs. Wood. Peter Tonge, November 12, 1980.
- Atmospheric Pollution: History, Science, And Regulation, pp. 84 – 85. Mark Z. Jacobson, 2012. Backed up on this site for archival purposes.
- The Living Age, Volume 195, page 499. 1892.
- Union Of Concerned Scientists, Coal And Air Pollution.
- Fumifugium: Or The Inconveniencie Of The Aer And Smoak Of London Dissipated Together With Some Remedies Humbly Proposed By J. E. Esq; To His Sacred Majestie, And To The Parliament Now Assembled. 1661.
- The New York Times, Why The Great Smog Of London Was Anything But Great. Eric Nagourney, August 12, 2013.
- USA Today, Mystery Of London Fog That Killed 12,000 Finally Solved. Jane Onyanga-Omara, December 13, 2016.
- BBC Future, The Lethal Effects Of London Fog. Those numbers only count those who suffered acute effects — it’s difficult to say exactly how many contracted chronic and ultimately fatal health conditions.22Time, Everything To Know About The Great Smog Of 1952, As Seen On The Crown. Kate Samuelson, November 4, 2016.
- The Telegraph, Air Pollution In London Passes Levels In Beijing… And Wood Burners Are Making Problem Worse. Sarah Knapton, January 25, 2017.
- Chemicool, Carbon Element Facts. Dr. Doug Stewart.