Many, many years ago, I used to devour science fiction comics.

In one of them, astronauts from Earth conducted the first-ever exploration of Mars. They were really surprised when a huge alien hauled itself out of the sandy ground and pronounced, "My body chemistry is based upon the element silicon.”

Even if we can absorb the idea of aliens speaking English, that opening greeting was not exactly what one would have expected.

All the living creatures we know of on our planet, including us, have body chemistries based on carbon. This is why the study of carbon-based molecules is referred to as "organic chemistry.”

The reason terrestrial life forms use carbon is that carbon atoms can chain together forming huge molecules, containing other elements, such as hydrogen, oxygen, nitrogen and others. That gives the scope for putting together all the different chemical tools we need—amino acids, proteins and so on, for life as we know it. As far as we know, no other........

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