Although we occupy a relatively restricted corner of the universe, it is an important corner, because here we encounter a new dimension of matter: complex organization. Stars are believed to be basically simple in construction. Temperature gradients and layering of material undoubtedly exist, with different thermonuclear reactions of the type encountered in Chapter 8 occuring at different depths. There may also be convection cells and magnetic field structures within one layer, but even the largest star has none of the organised complexity that we find in a germinating seed. At the other extreme, imperfect as our knowledge of subatomic structure may be today, we still must conclude that atoms, by the criterion of germinating seeds, are relatively simple objects also. Molecules, and especially molecules built with carbon-atom skeletons, seem to be required to build up a sufficiently complex set of chemical reactions to create a living organism. The next eight chapters will be devoted to an examination of carbon compounds: the variety they can have, the many different properties that they can exhibit, and the way in which they serve as the raw material of life. But before entering the jungle of organic biochemistry, it may be well to step back and look at our starting point again, the universe.

The smallest objects on Earth that we can see with the unaided eye differ from the Earth itself by twelve orders of magnitude: twelve ten-fold increases in linear size, or a factor of 1,000,000,000,000. This is close to the limit of what we can imagine, because it is the limit of our first-hand experience.