"The problem of the origin of life is, at bottom, a problem in organic chemistry — the chemistry of carbon compounds — but organic chemistry within a… - Francis Crick

"The problem of the origin of life is, at bottom, a problem in organic chemistry — the chemistry of carbon compounds — but organic chemistry within an unusual framework. Living things, as we shall see, are specified in detail at the level of atoms and molecules, with incredible delicacy and precision. At the beginning it must have been molecules that evolved to form the first living system. Because life started on earth such a long time ago — perhaps as much as four billion years ago — it is very difficult for us to discover what the first living things were like. All living things on earth, without exception, are based on organic chemistry, and such chemicals are usually not stable over very long periods of time at the range of temperatures which exist on the earth's surface. The constant buffeting of thermal motion over hundreds of millions of years eventually disrupts the strong chemical bonds which hold the atoms of an organic molecule firmly together over shorter periods; over our own lifetime, for example. For this reason it is almost impossible to find "molecular fossils" from these very early times."