The miracle of carbon

Carbon is a versatile element and appears in nature as spheres, tubes, sheets and other configurations. Image: Michael Ströck

Carbon is necessary for all life. If the element carbon did not exist, scientists believe the universe would be sterile, no life anywhere. Among more than a hundred different chemical elements, only carbon has the atomic structure, with six electrons surrounding a nucleus with six protons, necessary to serve as the basis for such complex organisms.

We take carbon for granted, but it is miraculous that it exists. In the first seconds after the Big Bang, protons and neutrons came into being, but the universe was expanding so fast that the only three elements formed were hydrogen, helium and lithium. So how did carbon come into being?

Clouds of hydrogen and helium gas eventually condensed into the first stars. These collapsed by gravity under their own weight, and as they did so they became hot — so hot that some pairs of helium nuclei (two protons) stuck together to make beryllium (four protons). Carbon has six protons, so carbon could only be formed if another helium nucleus could attach itself to that beryllium.  However, that beryllium isotope with four neutrons is so unstable that it decays back to two helium nuclei in about a ten-thousandth of a trillionth of a second (10-16 seconds)! The third helium nucleus had to attach itself to that beryllium isotope almost immediately.

The astronomer Fred Hoyle (also the author of science fiction novels such as A for Andromeda and The Black Cloud) proposed that carbon nuclei must have an internally excited, short-lived state to boost the chance of a helium nucleus sticking to the beryllium before it decayed. Hoyle’s prediction was later confirmed by experiment. (Hoyle  also invented the term “Big Bang,” but he didn’t believe in it.)

Other crucial elements such as oxygen and nitrogen were also created by similar reactions in the hot dense furnace of the stars’ interiors. Then the stars exploded, throwing these elements into space. Over billions of years, new stars were formed out of this debris, and they exploded in their turn. Our sun and planets, rich in life-essential elements, resulted from a third or fourth generation star exploding.

Amazingly, if the strength of the nuclear force between protons and neutrons after the Big Bang were different by less than 1%, carbon would be extremely rare, and the universe would be devoid of life. But here we are! There are several other ways in which the physics in our universe seem to be “just right” for life, known as the Goldilocks Principle. Food for deep thought!

This is a version of an article that originally appeared in Positively Naperville.