One of the most extraordinary things about our universe is the number of different atomic elements it has, each with its own special properties, such as helium, sodium, oxygen, silver, lead, hydrogen, and gold. (An element cannot be broken down into simpler substances. Compounds, on the other hand, are made of combinations of atomic elements. A water molecule, for example, has two hydrogen atoms, and one oxygen atom.)
Without such diverse elements, you could never get complex life forms. As I mentioned in the last section, when the universe began you only had the simplest kinds of elements -- hydrogen and helium. But hydrogen can only bond with one other atom, and helium doesn't bond at all. So for a while there was nothing in interstellar space but helium atoms and hydrogen molecules (made of two hydogren atoms).
Eventually this boring state of affairs changed. Most of the atomic elements in your body were forged in the core of a massive star (about 10 times bigger than the sun) and distributed by a supernova, the enormous explosion that occurs when a large star dies. (These explosions are so big that they shine as bright as an entire galaxy.) Our sun is, in fact, a second or third generation star. It was formed when gravity pulled together the remnants of previous stars that went supernova.
If it weren't for these ancestors of our sun, there would be no carbon, oxygen, or nitrogen -- the three main kinds of atoms that, along with hydrogen, make up your body and most living things. In fact, if the Big Bang had been only slightly more powerful, the massive stars needed to quickly synthesis the elements and then explode as supernovae would have been too rare, and our solar system would have been composed mostly of hydrogen and helium. And these atoms are too small and light to form solid objects on their own.
Here's the periodic table of elements. Hydrogen and helium are marked as "H" and "He." Basically nothing else on this chart would exist if the Big Bang had been only slightly more powerful. (And remember, if it had been slightly less powerful, you wouldn't have any atoms at all -- only black holes.)
But what's so special about carbon, nitrogen, and oxygen? Why were these particular atoms needed to make up living things? The answer to this question is actually very interesting, but I don't have space to go into the details here. (If you're interested, find an organic chemistry textbook and read the first few chapters.)
The basic idea is this. Certain kinds of atoms are good at making strong bonds (so-called "covalent" bonds) with other atoms. Hydrogen can only make one such bond, oxygen can make two, nitrogen can make three, and carbon can make four. If there were only hydrogen, you could have pairs of atoms bonded (H2), but nothing else. If there were only hydrogen and oxygen, things would still not be very interesting. You could theoretically have chains of oxygen atoms strung together, but in practice more than two oxygen atoms in a chain will not form a stable compound. Nitrogen is similar in this respect. Only carbon has the ability to form stable molecular chains (and perhaps silicon, a much heavier element). In this way, carbon can form indefinitely large structures, such as the proteins that make up animals, and the cellulose that makes up plants. DNA, which is just a long molecule that can store information, is another important structure made primarily of carbon. In fact, there's an entire field of study devoted exclusively to carbon-based compounds -- organic chemistry.
But carbon is only part of the story. The structure of our planet, for example, is largely dependent on an abundance of iron -- it forms the liquid core and provides a strong gravitational pull and a magnetic "shield" that protects us from the ions emitted by the sun. Oxygen is important because it is a key component of water, and of the atmosphere. Sodium, potassium, and other ions serve essential functions as electrolytes in most animals. Ultimately, it is the richness and diversity of atomic elements -- their varied structure and properties -- that has proven most important in the rise of life and human civilization. One can easily imagine a universe with a different set of elements that could still give rise to life and intelligence -- but only if those elements were diverse enough to combine into interesting, complex structures.
The theme that I am touching on here is creativity. For a world to be creative, it must show properties such as richness, diversity, and stability. This is the point of view I'm going to use in the coming chapters to examine the evolution of life, and the rise of civilization. Again and again we will see that our world has just the right properties to allow living things to evolve in divergent, complex, and interesting ways. This is important to understand because it will also eventually form the backdrop of my account of the rise of human values, ethics, and spirituality.
Appendix: The Physics of Chemistry
In this appendix I explain a few more details concerning the properties of atoms. For a more thorough treatment, you'll really need a physics textbook.
Physicists have observed hundreds of different kinds of particles, but only three of them ever combine to form atoms: electrons, protons, and neutrons.
Electrons are tiny -- about a trillionth the size of a pea. Electrons have what physicists call "negative charge," which means that they repel other negative charges, and attract positive charges. You can observe this effect when you rub a balloon on your head. The balloon collects electrons from your head and becomes negatively charged. Your hair, which is now positively charged, is attracted to the balloon and stands on end.
But why does your hair become positively charged when it loses electrons? Because now it has extra protons, which are positively charged. Most atoms contain an equal number of protons and electrons. In this state, the atom has a "neutral charge," which means that it does not attract or repel other atoms. Atoms that lose electrons have extra protons and become positively charged. But because positive charges attract negative charges, most atoms do not stay this way for long, and eventually attract extra electrons and become neutral again.
You've just learned the most fundamental rule in chemistry. Atoms like to have an equal number of protons and electrons, because opposite charges attract, and like charges repel. Much of chemistry is ultimately explained by this rule. Covalent bonds occur because certain atoms have an uneven distrubtion of electrons around the nucleus. Parts of an atom that have more electrons have a somewhat negative charge, and can attract parts of other atoms that have a somewhat positive charge. (Keep in mind that this way of thinking about it is somewhat inexact; it would require a mathematical treatment using quantum mechanics to provide a full explanation.)
But why is chemistry important? Because everything that happens in your body is chemical. All living things are really walking chemistry labs. Chemical reactions give you energy, send signals through your body, and even read the code contained in your DNA.
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