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Carbon is the element that forms the backbone of all long, complex molecules and as a result, makes up about 18% of the human body.

Like many elements, it was created within the core of a star and expelled into space before finding its way down to Earth.

Carbon’s importance comes from two attributes. It’s the most common element whose atoms have four electrons in their outer shell.

This means that carbon can form up to four bonds with other atoms. It’ll often use two of them to form bonds with other carbon atoms, creating long chains while having two bonds left over to interact with other atoms.

This opens the door for an extraordinary range of possible compounds, so much so that carbon has an entire branch of chemistry to itself called ‘organic chemistry’, and makes it by far the most important element for all known forms of life.

Here are some examples of simple carbon chains.

Each ‘C’ is a carbon atom, and each ‘H’ is a hydrogen atom. Carbon can form molecules with many different elements to create substances with unique properties.

It doesn’t take too much more imagination to picture enormously complicated molecules strung together with carbon like in the image below. Each dark grey ball is a carbon atom, and each white ball is a hydrogen atom.

Long, interlinked carbon chains.

Even the shape of the chains will create substances with totally different attributes. Carbon forms graphite, diamonds, carbon nanotubes, and many other substances just by arranging its own atoms differently.

A diamond and a lump of graphite, usually used for pencil lead

Graphite and diamond are two ‘allotropes’ of carbon, meaning they are both made from 100% carbon, but the atoms have arranged themselves in different ways.

The different structures made by carbon.

We’ve discovered over 10 million variations of carbon molecules (more than any other element) but it’s estimated that this is just a fraction of the total number that’s possible.

This huge range of molecules with different properties is the basis of life as we know it, and it is why life is said to be ‘carbon-based’.

For example, carbon chains are at the heart of the essential molecules of life, like carbohydrates, fats, sugars, proteins, alcohols, as well as DNA and RNA.

For such an important element, it’s fortunate that it is so abundant. The ‘carbon cycle’ is what we call the movement of carbon across the Earth, often moving from one molecule to the next and through countless living creatures over millions of years.

For instance when a sapling plant grows, it needs carbon to make sugars, DNA, and other molecules for its new branches and leaves. But it can’t just built them out of nothing. It will absorb carbon dioxide out of the air through its leaves, reconfigure it into the molecules it needs, and keeps growing. Most of the mass of a plant comes out of the air in this way.

Forests like this Redwood forest are huge carbon ‘sinks’, pulling carbon dioxide out of the atmosphere and into their bodies.

When an animal eats a plant it absorbs its sugars and other molecules, eventually breaks some of them down, and exhales carbon dioxide. For instance when you exercise and lose a few kilograms of fat, you are actually exhaling most of it as kilograms of carbon dioxide.

This is how plants and animals exist in sustainable balance with each other – the waste products of one create the resources of the other.

Earth’s carbon cycle.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.