In Our Time - Carbon

Episode Date: June 15, 2006

Melvyn Bragg and guests discuss Carbon. It forms the basis of all organic life and has the amazing ability to bond with itself and a wide range of other elements, forming nearly 10 million known compounds. It is in the food we eat, the clothes we wear, the shampoo we use and the petrol that fuels our cars. Because carbon has the largest range of subtle bonding capabilities, 95% of everything that exists in the universe is made up of carbon atoms that are stuck together. It is an extraordinary element for many reasons: the carbon-nitrogen cycle provides some of the energy produced by the Sun and the stars; it has the highest melting point of all the elements; and its different forms include one of the softest and one of the hardest substances known. What gives carbon its great ability to bond with other atoms? What is the significance of the recent discovery of a new carbon molecule - the C60? What role does carbon play in the modern chemistry of nanotechnology? And how should we address the problem of our diminishing carbon energy sources? With Harry Kroto, Professor of Chemistry at Florida State University; Monica Grady, Professor of Planetary and Space Sciences at the Open University; Ken Teo, Royal Academy of Engineering Research Fellow at Cambridge University.

This BBC podcast is supported by ads outside the UK. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio 4. I hope you enjoy the program. Hello, carbon forms the basis of all organic life and has the amazing ability to bond with itself and with a wide range of other elements

forming nearly 10 million known compounds. It's in the food we eat, the clothes we wear, the shampoo we use and the petrol that fuels our cars. Because carbon has the largest range of subtle bonding capabilities, 95% of everything that exists in the universe is made up of carbon atoms that are stuck together. It's an extraordinary element for many reasons.

The carbon nitrogen cycle provides some of the energy produced by the sun and the stars. It has the highest melting point of all the elements. And its different forms include one of the softest of substances, graphite, and the hardest known to man, diamond. What gives carbon its great ability to bond with other. atoms? What's the significance of the recent discovery of a new carbon molecule C-60? What role does carbon play in the modern chemistry of nanotechnology and how should we address the problem of our diminishing carbon energy sources? With me to discuss carbon as a Harry Crote, Nobel Prize winner

and Professor of Chemistry at Florida State University. Monica Grady, Professor of Planetary and Space Sciences at the Open University, and Cantillo, Royal Academy of Engineering Research Fellow at Cambridge University. Monica Grady, can you give us an overview of the importance of carbon and then a definition of it, please? Well, I think part of the overview came in your introduction there. It is everywhere. It sneaks into every niche of life. Physics, chemistry, biology, geology, technology, economics and ethics.

Carbon is there, absolutely everywhere. And it's all based on the structure of the atom. with its very, very special properties. We think perhaps of carbon, as you say, with graphite, the pencils that we write with, making up the DNA molecule on which all life is based. It's there, it's in the atmosphere, the stuff that we breathe out,

it's necessary for plants. It's everywhere. And it's all based on this tiny little atomic structure of six neutrons, six protons, six protons, six electrons. It came, it wasn't formed in the Big Bang, but it's been made in stars ever since. And there are different brands of carbon, if you like.

There's carbon 12 is the stuff is a carbon atom that has a weight, if you like, or a size of 12 units. and that is the standard against which all other elements are calibrated. Everything is given relative to carbon 12. But there are some small amount of carbon which has a slightly different unit, which is carbon 13. There's another type of carbon which is radioactive, which decays,

which is 14 units, which allows us to do radioactive dating. So there's a whole different physical. of carbon, which allows us to look at different properties of the element. You say it wasn't created in the Big Bang. As a matter of interest, how do you know that? Well, the Big Bang didn't create any elements in the way that we know them. The Big Bang created matter and energy in space and time in the sense that this is where protons were produced, electrons were produced, which eventually clumped together to form the hydrogen atom. and then hydrogen molecules. And most stars, the stars like our sun, are burning hydrogen. They're fusing hydrogen together to make another element called helium.

And in some stars, in some very, very special stars, three helium nuclei can come together to make a carbon nucleus. And that's a very, very, very special reaction. I mean, theoretically, it shouldn't occur. Theoretically, we shouldn't exist, because to get three helium atoms all to coincide in one go is very, very energetically different. And Fred Hoyle, what, 50 years or so ago,

predicted that this reaction would actually occur. He predicted that we would be able to survive, that carbon would be able to be formed in some stars. And it's a prediction that we knew the answer to already, if you like, because we were there. But it's very theoretically strange reaction that produces carbon in stars. So another strange part of the history of our journey to sitting here in this studio, that's right.

It's, I mean, something, people have argued about something called the anthropic principle, which says, you know, everything is special and right just so that we can exist. And this is one of the odd things. things as well that, you know, just the very carbon atom itself is a very, very special. If something was tweaked, just the resonant energy of that reaction was tweaked to just a tiny, tiny amount, then the carbon 12 atom wouldn't have formed. Kentier, can you tell us about the atomic structure of carbonate and maybe illustrated by telling us why diamond is unique being the hardest natural substance known to man?

Yes, Melvin. The carbon atom, as Monica described, has six protons. six neutrons and six electrons, but what makes it extremely versatile is actually the way it bonds with itself or other elements. So in carbon, there are three types of bonding that is possible. Technically, it's called SP1, SP2 and SP3 type bonding. The first type bonding is where carbon forms a linear type bond, so you get a chain-like structure. The second type of bonding, which is the most abundant and most stable form of carbon is the SP2 type bonding in such a structure. I'll try and describe it over the radio.

You get a single carbon atom bonded to three other carbon atoms in sort of a triangle. So you have the carbon atom in the center with three others at the vertices of the triangle. Now, when this subunit then forms a lattice, that is a larger structure, you get a honeycomb structure. And this honeycomb is called the graphene sheet, which then collectively many sheets of this together forms graphite. And the third form of carbon type bonding is the SP3 type 1. And in this particular case, you have to now imagine a carbon. carbon atom in the center and four other carbon atoms at the vertices of a tetrahedron. So this is quite different to the SB2 bonding, which form a planar structure, because now a

tetrahedron is a three-dimensional structure. So when you have this tetrahedron, you have a material then that is very isotropic. That is, it has nice uniform properties throughout its structure, and this is the basis of diamond. So we all know Diamond S being a very, very, very hard material. In fact, it is the hardest material, the hardest naturally occurring material on the planet. And this is due to the fact that the carbon atom is extremely small and hence forms very, very strong and very, very tight bonding in all directions in three dimensions. You were looking long earlier at your models then, Ken.

Yes, I have been. You brought them along, you have them in front of you, and you kept glancing away to them, but there's nothing we can do about it. Well, we could put them on the web after this show, I think. But basically, the two models I have in front of me, one of graphite and one of diamond. The key difference between these two models is...

They're like lots of black grapes. Yes, well, they have what's called ball and stick models, where the balls are the nuclei of the carbon atoms, and in between them, the sticks, are the bonds. So for the graphite one, you can see here, Melvin, I will put it on the internet later on. You have the sheets or the honeycomb sheets of carbon atoms, which are then separated by quite a large distance to the other sheets. Because these sheets now slide over each other very easily, graphite is very soft, okay, and it's very ductile in that sense. It's very very

very amelible, it's different to what we have diamond, which is a very rigid three-dimensional structure. These are two ancient, by science standards, ancient known appearances

of carbon. There are two pure antaropes, the diamond and the graphite. A third was discovered by you hiring your team, not many years ago, a couple of decades ago, and you found C-60, which the Buckminster Fullerene, to give it his full name,

which has been acclaimed by people and taken up as a very, very important discovery indeed. How did you arrive at it? Well, I was actually interested in this problem of why carbon was here in the first place and was interested in the work that we'd done in the mid-70s. with carbon chains and realized that the journey to us on the earth and the carbon to us came by these stars that produced carbon by nuclear synthesis. And I wondered what form the carbon was as it was blown out of these carbon stars and thought it might be changed.

And when we simulated the conditions, this was with Rick Smalling and Bob Curl and colleagues in Rice University in Texas, we discovered that, yes, you're going to. it did come out as carbon chains, but also this ball came out, which had a C-60 molecule, which had the same structure or the same pattern as a soccer ball, and that was a big surprise,

totally unexpected to us, and I think, in fact, the whole chemistry community as well. Can you be even more specific describing the C-60, because it has proved to be very important. The 60 stands for something, doesn't it? Yes, well, the 60 carbon atoms. If you take a soccer ball structure with 12,000, pentagons and 20 hexagons.

All the 12 pentagons are isolated. Often they're painted black, so you can see them all separated by the white hexagon. If you put a grape, as you say, as you call it, not a very tasty grape, by the way, but at the intersection of the various patches on the

soccer ball, you'll find that there are 60 there. And it will have that same pattern. And so the stitching, well, there could be the bonds and these grapes that you put at those intersections. could be the nuclei. But remember that the soccer ball

is about 100 million times larger than the C-60 molecule because the C-60 molecule is one nanometer, 1,000-millionth of a meter in diameter, almost exactly. And it's been a somewhat become sort of iconic image of the nanometer or nanoscale technology that we have today, or think about today.

Apart from the excitement, discovering something that was just the third pure form of this very, very important element. It seems to have been immediately taken up and recognised all around the, right across the waterfront. So can you just say, summarise why it has been seen as so important? Well, I mean, or is seen as important. Well, I'm not sure how important it is. It was important enough to the Stockholm Committee to give us the reward. But whether it turns out to be quite as important to that still remains to be seen.

I think the thing that was interesting was that first of all it was the third form here were these two forms diamond and graph that had been known since time immemorial and they're lurking almost like the third man in the streets of Vienna when the lights turned on or whatever was this beautiful molecule which artists and architects

seem to be drawn to and not only was it beautiful but it also was a new form with its whole new area of chemistry and that, I think there must be 5,000 or maybe even 10,000 papers on the chemistry of this molecule. It was then recognized that it had some rather remarkable properties. The first thing, that C60 itself was the smallest that could be stable, or some smaller ones could form. But if you elongated them and thought of it as a balloon,

you can make long balloons, okay, or round balloons. If you made the longer ones, they were recognized as what are called, nanotubes. And these nanotubes now seem to be possibly, if we can control the structure of these, the strongest materials that would ever, could we believe, could ever be made with tremendously exciting tensile properties, electrical properties and other things. So the C-60, which is the sort of the father of all these different

structures, the larger ones are giant phoomeres which might be symmetric, but then the tubular ones which are really very exciting and I think the reason that really the scientific community the engineers, material scientists are really fascinated that if we can produce this on a large scale it would revolutionise civil engineering as well as electrical engineering. You call them Buckminster Fullerings. Well, I called C60 the original one when we had it.

I mean on the day we were writing the paper I suggest we call it Buckminster Fullerene, because Buckminster Fuller's dome at Montreal in 1967, which my family, my wife and little boy, Stephen, visited in 1967 was a magnificent building, which once you've seen it and once you've been it, you never forget it. And it was that image that was in my mind and the minds of my colleagues, certainly Rick Smalley, who had also visited,

which led to our rational, of what the C60 structure might be. At that point, I suggested Buckminster Fuller-Een, and the in ending is important because it's like benzene that is important in chemistry. So the C-60 molecule is called Buckminster Fullerine, and then the Fullerines, it was shortened to the whole family.

The elongated ones, which are Fullerines too, are really called nanotubes, because you can imagine that really the main property of these is that they're tubes of graphite, like straws where this structure that you've just been discussing is actually a graphite graphene sheet rolled up and that has

remarkable properties. Let's talk to the physics of carbon. Can you explain how electrons work within atoms and give us an example of this? Well, the electrons in the carbon atoms are responsible for the bonding. And that's very, very important here because it is the ability of carbon

to form either single bonds, double bonds, or triple bonds that gives rise to its ability to form all the different various compounds and also the allotropes of carbon that we have here today. And for example, if we look at something like methane, which is most abundant in natural gas, it is a single bonded structure. Whereas if you look at something like acetylene,

it is a triple-bond, you have two triple-bonded carbon atoms. And the difference between these two gases is that you get a lot more energy from the acetylene molecule when you burn it. And that's why you use that in welding, whereas natural gas is used in, for example, in heating or cooking. But more importantly, not only does the bond of the carbon atoms store the energy, and release the energy,

the electrons in carbon also determine their electrical and electronic properties. So, for example, if we, go back to graphite, we have in the carbon atom actually four out of its six electrons in its outer shell. And it is these outer shell electrons that determine the electronic properties or electrical properties of the material. So in graphite, if you recall, I mentioned that it forms three bonds. So three of these four electrons are used up. And you actually have one free electron then. And this one free electron then gives graphite the ability to to conduct electricity. And also, because of this free electron,

it gives graphite then the appearance of a metal. It is shiny, because metals also have these free electrons. Okay, but then, if we now move to Diamond, in Diamond, all the four electrons are involved in bonds, so there are no more free electrons in the whole structure. Because of that, right? Diamond is basically an insulator. it has a very high bandgap and it is transparent,

totally different from graphite. And very importantly as well, these electrons which form the bond, they form a very, very tight bond in diamond. And the strength of this bond is what gives rise to the strength of diamond. What Harry mentioned just now, which was the nanotube,

actually being a sheet of, of graphite rolled up, okay, you then now have very, very strong bonding in one axis, because when you have a sheet of graphite, it is bonded very strongly in its plane, right? So when you roll it up, you now get all the strength of it in one axis. However, you still have the free electrons there, and that then gives it the important properties such as electrical conductivity and also other electronic properties, which it could, then be used as also a semiconductor. Thank you. Monica, great. Can you take us on about the

arrangements of the electrons in carbon and why this is very important to the ability of carbon to inhabit so much and to drive life, really? Well, as Taya was saying, carbon has six electrons and the way they're organized is that there are two inside sort of close to the nucleus of neutrons and protons and four on the outside.

And the way bonding works is atoms like to give or take or share their electrons to form these bonds. Can you just explain absolutely clearly to listeners why bonding is so important and why the multiplicity of carbon bonding makes it so extraordinary and unique in the elements? Well, carbon is the only element that has this absolute specific electronic structure. The 100 odd elements. Of the 100 and odd elements. I mean, all elements are made up of protons and neutrons and electrons, but they all have different numbers of these particles.

And so carbon has this unique number. And it's because of this unique structure of having four electrons that are loosely bound enough for it to be able to share four of those electrons and make these bonds. No other element can do that. Other elements have four electrons available for sharing, but they're a bit further away from the nucleus so they can't grip on to electrons from other atoms in the same way.

So, for instance, silicon has, which is very closely related to carbon in a lot of ways, also has four free electrons available to be given or shared. But because those electrons are slightly further away from the nuclear, which is where all the strength is, the silicon atom can't cling on to other electrons in the same way as carbon can. And bonding is what atoms want to do. They want to become stable, they want to form stable relationships,

they want to get this outer part of their structure full of electrons, if you like. So they want to either give an electron away to have an empty shell or get an electron in. This is a very sort of simple way of looking at it to have a full shell on the out of it. The sort of, if you think of the structure of an atom as being this sort of shell-like structure,

atoms like to have, if you can give them these sort of senses, they like to have a full shell, either by getting rid of an excess electron or grabbing in somebody else's electron. But carbon can share, and so it can get its full shell by sharing all these electrons, by making itself part of a community.

And then, you know, this one can share with that one, which can then share with another neighbour, with another neighbour and another neighbour, you know, to infinity. And sometimes, actually, I'm not going to make a chain, I'm going to go and I'm going to become a ring, a circle, so this end can join up with this end. And then that ring can join to that ring to that ring. So you have a huge great network of molecules,

that can start to bring up. And, oh, actually, although this carbon is bonded to all this hydrogen, perhaps, actually, I'd like to have a nitrogen there instead, or an oxygen, or an oxygen and a hydrogen combination. And so you get this huge, magnificent network of organic chemistry where you get slightly different elements feeding into these chains, and you get different properties. This one is an amino acid.

This one is a carboxylic acid. This one's got a double bond and a... to an oxygen, all these sorts of things. So you get this infinite network of combats. Harry Carter, you've talked a little about nanotechnology. Can you define it for us and tell us the place that carbon plays in it? Well, I've always said it's not a new area at all. Dalton showed that there were atoms and molecules in 1803, I think,

and I believe it's at least as old as that. It's to some extent a new perspective, which has been recognised by people outside chemistry. Chemists have been working with nanoscale objects called molecules since there has been chemistry. So of you, you've been drinking water. The nanoscale, you've been drinking alcohol, whatever. These are all nanoscale things.

I think what is interesting is that now... How is my drinking water? There's no alcohol on the table, listeners. How is my... I thought this one. Oh, no, it's Glenn Livert. It's space-eyed Glenn Livert. I mean, you know, I thought it was.

I'm only joking. What, how, how, I was, no, because it's a very useful graphic illustration. Why is my drinking water to do with nano? Anybody's drinking water. Because these are nanoscale objects. They're molecules. And molecules are about a nanometer on average in size. What I think has happened is in the...

A nanometer is 100 millionth. It's a thousand millionth of a meter, a 10 to the minus 9 of a meter. And to imagine it, one imagine, John Hare and my colleague suggests that you think of it in these terms, that the ratio of a soccer ball to the earth is the same ratio as the C60 or roughly the water molecule is to the soccer ball. If that's helpful, then hopefully it is helpful. It might be. But anyways, the ratio is 10 to the 8 in that case at about. But I believe it's actually a recognition by people who are in,

say engineering and physics and other areas of how important chemistry is. And thinking about these materials on the basis of the bonding between the atoms. In fact, Feynman was asked, what is the most important piece of information to be passed on to a next generation? If all knowledge was lost, he said that there are little things called atoms, and at long distances they attract each other, and at short distance they repel. It's the chemical bond, because everything is made of atoms and the way that the elective. hold those atoms together is chemistry, and that's how life forms, the materials,

the adhesives, the metals, you name it, a whole world by and large, is based on the chemical bond. Now, I don't think it's new. I just think nanotechnology or nanoscience, which is the fundamental area in the nanotechnology, which is the applied area, are new names for a new perspective of engineers, material scientists, physicists,

who have really thought from a top-down perspective and now think maybe we can construct interesting new devices and develop new tensile properties if we can build them up with really well-controlled chemistry. Now chemistry is a very mature subject and we've learnt really how to make small molecules but can we actually now construct big molecules with very close control.

In the way that DNA actually is a, very large molecule with a very specific structure. That's a fantastically well-specified structure with an error rate of about 10 to the minus 9. You know, one error in about 1,000 million. Otherwise we wouldn't live because there were too many errors would come in. Can we actually develop a chemistry, a bottom-up assembly of large systems

with that sort of exactly specified control? And it's a tall order. If we can, then we shall, I think, be able to produce computers, supercomputers in your wristwatch. Perhaps we'll be able to construct materials with incredible strength, maybe material 100 times stronger than steel, one-sixth the weight. If we can do that, it's a tall order. I don't know whether we shall be able, but it should be possible. And so it's a new perspective rather than a new area. Ken.

As Harry was saying, nanoscience is not new. However, what is probably new with all this nowadays is the technology part. Nanotechnology is actually the convergence of the different disciplines in one common size. So as Harry was mentioning, the atoms have grown to molecules and then to bigger molecules, which are nanoscale. With electrical and electronic engineering, people have been making microscale chips, which are now going down to the nanoscale. Then you also have biology, which you have, for example, bacteria, which is very, very small. small on the microscale and approaching the nanoscale as well. So it is the convergence of all the different disciplines into one nice area, which then you can really cross-fertilize. For example,

you can now then use electronic engineering in which we can get data from and do processing on to probe molecules and also to probe bacteria then, in which you can form biological sensors then which then build up more important systems altogether. I just wanted to ask though, how easy is it to control this? I mean, Harry was talking about the discovery of C-60 and it was sort of by accident almost and they got these things. How can you now, when it comes to nanotechnology, control, saying, right, okay, I specifically want to make a long, long tube.

I mean, isn't that one of the challenges? Now we know about them is actually making them. Yes, Monica. So traditionally, being an electronic engineer at heart, we've been going what's known as top-down. So we start off with a bulk material, which is something large, something macroscopic, something we can hold and feel. And then we define it as smaller and smaller structures. And as I was describing before, we're now converging at this nanoscale field. And as Harry said, when we are in the nanosize, we have to use a different approach now. we are going bottom up.

So that is we grow the structures now, using chemistry. We grow the structures of a particular diameter, a particular length, and a particular orientation. So now we have a meeting point in between the two disciplines. And it is this meeting point which then gives rises to the new devices which would revolutionize the world. Well, Monica's point is the important one, and the one I hinted at earlier, If we can control the growth from the bottom-up approach, then we shall actually have a revolution in materials, engineering, and electronic engineering. But it's a tall order.

And I say we've spent 200 years developing the chemistry we have at the present time. But at the moment, we don't have the control over carbon chemistry. I mean, there's this wonderful area of organic chemistry, where we've learned such a lot. We know there's biological chemistry where there's incredible control. all over. This is actually bottom up assembly. We are actually the examples of nanotechnology. Life has done it.

Shown it can be done. Everyone. We're built up from a blueprint of small molecules all put together into this incredible living system which all these molecules can work together for us to be able to speak. That's incredible. We are not even on the first rung of this ladder with materials particularly carbon

because although carbon has an organic chemistry when it's attached to hydrogen, it's soft materials and things like this and liquids and gases and stuff like this, when it's by itself, it's this hardest material of all. And there is actually no pure carbon chemistry. So the control that we have over nanotubes

is very, very limited, almost non-existent. But it should still be possible one day to work out how to develop that. Yeah, I mean, that's a, interesting point about the carbon not being the pure chemistry. And one of the things I'm sort of fascinated by is what we can actually use these fullerine molecules for in terms of storage, in terms of poking things in.

You know, put gases in them. Is this another way of developing a technology in terms of a useful material, making cages for storage at the nano level? I don't know. They will have uses. of those kinds. But the excitement within the scientific community is really

I think going to be can we build structures as complex as we are? Can we develop a chemical synthetic technology which can build really from a bottom up approach the elements that we need to produce computers and other devices? In the moment we really are a long way from that.

Kentia, the key use of carbon today seems to be in energy production. How is carbon used in that? Carbon is, of course, the basis of all fossil fuels. For example, in coal, in petroleum. So when we burn carbon,

it combusts and that releases energy. That gives us heat. We then convert the heat into other types of energy, for example, electricity or light. Now, that is one type of energy production, and it is the major form that we use and is the basis of society today, but also another form of energy production, or energy, well, we start with energy storage, is in photosynthesis. There, we have plants which take the energy of the sun in a chemical reaction

called photosynthesis to produce carbohydrates. And we then consume that, which then release energy in our body so that we can walk, we can talk, we can go about our life. So that is how carbon is used in terms of energy, storage and production. Are there, Monica, are there inherent problems in relying on carbon as an energy source?

Enormous problems. We have the carbon cycle starting with a green plant which uses sunlight as said to photosynthesize, which then lives and grows and then decays, becomes part of a rock which is compressed, produces oil or gas or coal, and that takes millions and millions of years of geological processing. And we are using up those fossil fuels at a tremendous rate.

and the rate at which plants and animals are dying and becoming fossilised is very, very, very low compared to the rate at which we are using up their fossilised remnants. And so we are mining our fossil fuels and using them and squandering them and frittering them in a way which is completely unsustainable. It's something we have to look at different ways of producing energy. We cannot go on using our fossil fuels because we will run out. Yeah, I think that's the issue that almost every scientist now looks at, and I think

everybody outside the scientist community thinks that we're going to solve it. We're using fossil fuel, its estimates, one million years worth of fossil fuel per year. Well, that obviously is pretty quick rate. What have we got to do? We've got to do something unbelievable. We have to store the energy that we get in one year from the sun. in such a way that we can use it at the same rate for sustainability issues. And unless we solve some of the problems very quickly, we will not be able to survive and there will be a breakdown, I believe, in society. The major issue that plants actually have solved,

but not efficiently enough for us to be able to do that, is to split water into hydrogen and oxygen. If we can solve that problem... Why is this... With sunlight. One photon can't break the hydrogen-oxygen bond. Two photons are required, and the two-photon process is inherently very sort of inefficient. But one-photon process, if it could happen, there would be no water.

So it's a good thing that's not. There would be no water on the earth. On the other hand, plants have developed this really complex structure around them, with leaves and growing and all this stuff, and they actually can do it. And they've got a very clever way of taking one photon effectively and storing the energy and then doing it in two stages. We have to solve that problem, I think, within the next 50 years.

And if we don't, we are on the way out, really. But as a corollary to that, and continuing this idea of using the fossil fuel, I mean, we burn the fuel, what do we produce? We produce carbon dioxide, another form of carbon as a gas, in the atmosphere, which is building up and building up and leading to global warming. And so we've got two problems. We're using the fossil fuel, which we are not going to keep on,

we're not going to be able to keep doing because it's running out, and we're converting it into this sort of useless thing called carbon dioxide, which is preventing the sun's radiation being re-radiated back out into space, which is gradually heating up our atmosphere, melting the ice sheet, and so on and so forth. So this is carbon cycling, the carbon cycle, at its most worrisome in this imbalance. One of the most important things here is, of course, sustainability. So although Monica described the action of bringing carbon into the atmosphere,

we need some sort of carbon recycling, that is to bring it back down again. And the only way that we can do that today is through planting. And, you know, if we now look at, take an average individual in society, we produce from our usage of electricity, etc., on average, around 40 kilograms of atmospheric carbon. So effectively... Is that per year? Per year, that is.

Each individual person. Yeah. Yeah, okay. Equivalent of burning fuels, you know, driving your car, turning on the lights. All the 6 billion people or so. Yeah. So this is a tremendous amount of carbon

that we put up into the atmosphere. And the only way we can bring it down is through plants. And it is said that we need to plant on average. or each individual needs to have 40 plants on average to bring it back down. 40 trees or plants? 40 plants, 40 shrubs to get it down. Sorry, just a second. Is this 40, plant them and leave them, you've got your 40, you can stop.

So if let's say you have a new human being, you have a new baby, you should plant 40 plants because that, you know, through photosynthesis and all that, those 40, plants will grow at the same rate as your consumption of carbon to produce the carbon back into the atmosphere. The problem is how much land is there to do this because growing these plants is not

a trivial problem. It requires fertilizing. People think that these trees grow on trees. But in fact, we use 70% of all our food is grown by putting the Harbour Bush ammonia on the land, which uses

ammonia, is produced by hydrogen and nitrogen over an iron catalyst at a thousand degrees. The hydrogen comes from fossil fuel and the heating comes from fossil fuels. So even the food we're eating, which is grown and takes up the carbon, we're putting fertilizers on there at an enormous rate. I mean, we've got a problem or two here. But nanotechnology, if we can develop some of the clever methods that plants have done, if we can now learn from those to actually for the, you know, how the plants do photosynthesis,

and we can emulate that by developing nanoscale motors and machines that can do it. Maybe we'll solve this problem. What does it mean when you talk to your students about carbon and say we're mostly made of carbon, do they resent this? Do they think this is something that they don't want to hear? I don't think so. I think most people know that they're made of carbon, that the backbone of life is the DNA molecule,

and the backbone of the DNA molecule is the carbon atom. I think it's something that most people realize and accept and know that we're all part of a vast carbon cycle. I mean, the Gaia hypothesis from Jim Lovelock is all based on this sort of holistic view of not just the earth, but the solar system, the world, the universe, as this just cycling and moving of consciousness, carbon from different reservoirs, and we are just a small part of that.

And what humanity is done has tipped the balance. We have disturbed the equilibrium. If you look at a star, you get an equilibrium reactions in stars, which just based on chemistry and physics. As soon as you stick biology into the equation, you've got anarchy. Finally, Harry, when you discovered the C-60, you found that it existed in nature. And is it therefore possible to extract more of it from nature?

Well, it's a bit more complicated than that. You've all made it. Every time you lit a Bunsen burner, the flame is yellow, you actually made C-60 in large amounts. But the problem is a small molecule, and it was hot in the Bunsen-Mereux, as it hit the oxygen, you lost it immediately. So the amount that actually survived combustion is almost negligible. You can't.

So it was formed in the flame, but then it was lost immediately, and that's why we were so late. in discovering it. So when you lit a match, you form some C60. The C60 molecule is very small and very hot. As soon as it hits oxygen, it's oxidized and lost. So there is almost nothing in the atmosphere. It's almost certainly coming out of carbon stars, but it's difficult to see. So we still haven't seen it in space.

Well, we'll end with carbon stars. Harry Croto, Monica Grady, and Cantillo. Next week we'll be talking about the Spanish Inquisition. Thanks for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.com.uk forward slash radio four.