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Every form of life which has ever been discovered, regardless of its size or how it metabolizes energy, has one thing in common.
They are based on the element carbon.
Carbon is the most important building block for life. It holds a unique place on the periodic table, and it can combine with itself and other elements in so many different ways that there is an entire branch of chemistry devoted to it.
Learn more about the element carbon, its importance, and its future on this episode of Everything Everywhere Daily.
Carbon is a very special element. It is the sixth element on the Periodic Table and is estimated to be the fourth most abundant element in the universe, behind Hydrogen, Helium, and Oxygen. However, it is only the 15th most abundant element in the Earth’s crust.
If you remember back to my episode on Lithium, elemental abundance after hydrogen and helium does not correspond perfectly with atomic numbers.
Carbon is created in stars in a process known as the triple-alpha process. In the triple-alpha process, three helium atoms fuse together to create carbon.
There are three naturally occurring isotopes of carbon. Carbon-12, carbon-13, and carbon-14.
Carbon-12 and 13 are stable, but carbon-14 is unstable and undergoes radioactive decay. This is why carbon-14 is used for the dating of objects.
I’ve previously done an entire episode on radiometric dating, but suffice it to say by looking at the ratio of carbon-12 to carbon-14, you can determine the age of something. Carbon-14 gets locked in when something is alive and then decreases over time.
All of the things I’ve just mentioned are not what makes carbon special. What makes carbon special is its outer electron shell.
The outer electron shell for elements in the first row can hold eight electrons. Carbon has four electrons in its outer shell. This puts carbon in the goldilocks region of the periodic table.
It doesn’t want to get rid of its electrons like lithium which is further to the left on the periodic table, and it doesn’t want to grab electrons like oxygen which is to its right.
Because it has only half of its electron shell filled, it can combine with a wide number of other elements in a large number of ways. Not only that, but it can bind with other carbon atoms in many different ways
This makes carbon able to form incredibly large molecules. Polymers, proteins, and hydrocarbons.
It also can create double, triple, or even quadruple bonds with other elements.
For example, if carbon bonds with four hydrogen atoms, you get methane.
Likewise, if it has two double bonds with two oxygen atoms, you get carbon dioxide.
Or, it could have a triple bond with a single oxygen atom to create carbon monoxide. What makes carbon monoxide so dangerous is that only three of the four available electrons in the outer shell are filled. That last one wants to bind to something, and it likes to bind to hemoglobin in blood.
When it binds to hemoglobin, it prevents oxygen from binding, which can cause hypoxia. In fact, it can bond with hemoglobin 240 times stronger than oxygen can, which is why it is so dangerous. Even a small amount can prevent your body from using oxygen, even if you are breathing plenty of oxygen.
There are so many possible combinations of molecules using carbon that there is an entire branch of chemistry devoted to carbon: organic chemistry.
True story, I was once in a grocery store in New Zealand when I came across some table salt that was labeled as organic. All I could think of was, “no, it’s not. There is no carbon in salt.”
…that’s the kind of thing that I think.
The subject of organic chemistry, DNA, proteins, and hydrocarbons are all subjects for future episodes, as each of those can be the focus of a lifetime’s study.
This ability for carbon to create such a wide variety of molecules is why carbon is the basis for life and why living things are often known as carbon-based life forms. More on that in a bit…
Carbon also has the ability to bind with itself. Because it has four free electrons, it can do so in a number of different ways.
The different forms of carbon are known as allotropes. Each of the different carbon allotropes has unique and exceptional properties.
Perhaps the allotrope you are most familiar with is diamond. Diamond is carbon in a three-dimensional crystalline structure. The carbon bonds in a diamond are extremely rigid. Diamonds have the most atoms per unit volume, which is why it is so hard and so difficult to compress.
I’ve previously done an entire episode on diamonds, so I won’t belabor the point, but it is remarkable how different diamond is from every other allotrope of carbon.
The other common, naturally occurring allotrope of carbon is graphite. Graphite is a crystalline solid that is made up of layers of flat sheets of graphene.
Whereas diamond has a 3D crystalline structure, graphene has a flat two-dimensional structure. The carbon atoms are bonded in a hexagonal structure.
While the bonds between the carbon atoms are relatively strong within the flat sheets of graphene, the bonds between sheets are rather weak. This is one of the reasons why graphite is such a good lubricant.
Ever since the 19th century, scientists have known that graphite was made out of sheets of carbon graphene. However, they were never able to isolate graphene from graphite.
It was isolated for the first time in 2004 by a pair of researchers from the University of Manchester. They used what is officially called micromechanical cleavage to separate it, but it is more commonly known as the scotch tape technique.
They used a weakly adhesive substance to remove single layers of graphene from graphite which was only one atom thick. The researchers, Andre Geim and Konstantin Novoselov, were later awarded a Nobel Prize for their work in graphene research.
Fun fact: Andre Geim is the only person to have won a Nobel Prize and an Ig Nobel prize which is given for trivial scientific achievements. He was awarded his Ig Nobel prize for work on levitating a frog with magnetism.
For the longest time, diamond and graphite were the only known allotropes of carbon.
In 1985, a new form of carbon was discovered when carbon was vaporized in a helium environment. The result was carbon molecules with exactly 60 carbon atoms.
It turned out the new carbon was in the shape of a sphere. It was dubbed Buckminsterfullerene in honor of Buckminster Fuller, who popularized the geodesic dome, which looks like Carbon60. They are more commonly known as buckyballs.
There is an entire class of Fullerene molecules with different numbers of carbon atoms. The largest Fullerene molecule is a sphere with 3,996 carbon atoms.
The discovery of Buckminsterfullerene and the isolation of graphene had huge implications. It turned out that they weren’t that different from each other.
If you took a sheet of graphene and wrapped it around itself to create a cylinder, you could create what is known as a carbon nanotube.
Likewise, a carbon nanotube can be thought of as just a buckyball with a hole in it.
Why is this important? Because carbon nanotubes have some of the most remarkable properties of any materials which have been discovered.
For starters, carbon nanotubes have the highest tensile strength of any substance known. Tensile strength is the load a material can bear while being stretched. High tensile strength is important for things like cables and ropes.
In theory, a carbon nanotube with a cross-section of one square millimeter could support a load of 6,422 kilograms or 14,158 pounds. That means that something the size of a thread of dental floss could support the weight of three large pickup trucks.
If we ever wanted to build a space elevator that could carry objects up to geosynchronous, in theory, a cable made of carbon nanotubes or of a carbon tape of extremely long pieces of graphene could actually work.
Tensile strength isn’t the only incredible property of carbon nanotubes.
They also are incredible electrical conductors. Their use in transmitting electricity could revolutionize the electrical grid.
They also can exhibit semiconductor properties depending on how they are built. There is already work being done on next-generation computer processors. Researchers at MIT have already built prototype processors out of carbon nanotubes, which in theory, would be faster than silicon.
On top of that, carbon nanotubes can conduct heat incredibly well as have a high refractive index which allows them to bend light that goes through it.
These forms of carbon, whether they are in the form of a tube or a sheet, could revolutionize many industries. Everything including electrical transmission, computers, clothing, cars, and aviation.
If these forms of carbon are so great, then why don’t we use these forms of carbon in everything?
It turns out that creating tubes or fibers of any significant size is very difficult. Getting lengths beyond a few millimeters is difficult. The longest nanotube ever grown is only 50 centimeters, and that was done over a decade ago.
The key widescale adoption of carbon nanotubes and fibers will depend on the ability to develop large pieces cheaply and at an industrial scale. So far, this hasn’t been accomplished, and creating these forms of carbon is very expensive.
Before I talked about carbon-based life forms. All the life forms we know of, from viruses to bacteria, to worms on the sea floor, to people, are all based on carbon.
Many scientists and science fiction writers have wondered if it would be possible for a non-carbon-based form of life to exist.
The best candidate other than carbon would probably be silicon which sits right below carbon on the periodic table. Like carbon, it has four electrons in its outer shell, and for that reason, many have speculated that it could form molecules like carbon.
We obviously will never know if non-carbon-based life is possible until we find it, but the odds are slim.
We actually know quite a bit about silicon chemistry, and despite its electron configuration, it just doesn’t behave the same as carbon. For starters, when carbon oxidizes, it forms carbon dioxide, which is a gas under temperatures and pressures which allow for water.
When silicon oxidizes, it produces quartz, which is a mineral.
It has been theorized that maybe, maybe, such a life form could exist in lava or magma, but that would be beyond the boiling point of many lighter elements, which would make the creation of complex molecules more difficult.
Moreover, there is just way more carbon in the universe than silicon, and amino acids, which are the building blocks for DNA, have been found in interstellar space.
On top of that, silicon doesn’t tend to form double and triple bonds, and it has a larger atomic radius than carbon which affects bond angles, bond lengths, and bond strengths.
So, if we look for life outside of Earth, we should probably stick with what we know and look for carbon-based life.
Carbon is really important. Life, as we know it literally, couldn’t exist if it wasn’t for carbon. If we ever find life outside of Earth, it will probably also be carbon-based.
…and after a billion years of carbon-based life, it is possible that our lives could be transformed with new carbon-based technologies in the next several decades.
The Executive Producer of Everything Everywhere Daily is Charles Daniel.
The associate producers are Thor Thomsen and Peter Bennett.
Today’s review comes from listener Dempcity over at Apple Podcasts in the United States. They write:
Working Listener From Michigan
Consuming 10-minute snippets of information while I am at work truly makes my day more enjoyable and entertaining.
The quick yet thoughtful content of each episode keeps me excited for more.
Covering Globetrotters to Escobar’s Hippos I’ve found very few episodes that don’t strike my curiosity.
I am interested in English Bulldogs and The Appalachian Trail if your willing to educate me more.
Keep up the great work and I look forward to many more work days with you.
Thanks, Dempcity! If you are listening to the show at work, you can actually listen to the podcast to use the Pomodoro time management technique. You set a task and work at it in a focused manner for about 20-25 minutes….which just so happens to be the time of about two episodes, and then get up and take a break before you go back to whatever you were doing.
Remember if you leave a review or send me a boostagram, you too can have it read on the show.