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About Minerals

Fossils

It isn't easy to become a fossil. The fate of nearly all living organisms - over 99.9 - is to compost down to nothing. When the spark is gone, every molecule will be nibbled off or sluiced away to be used in some other system. Even to make it into the small pool of organisms - the less than 0.1, that don't get devoured, the further chances of becoming a fossil are still very small.

In order to become a fossil several things must take place. First - die in the right place. Only about 15 of the rocks can preserve a fossil, so it is no good to "keel over" on granite.

The deceased should come to rest to be buried in sediment, where it can leave an impression, like a leaf in wet mud, or decompose without exposure to oxygen , permitting the molecules in bones (and occasionally softer parts) to be replaced by dissolved minerals, creating a perfect copy of the original. Then as the sediments are carelessly pressed and folded and pushed about by geological processes, the fossil must still however maintain an identifiable shape. Finally, above all, after tens of millions and hundreds of millions of years it must be discovered and recognized as something worth keeping.

Only about 1 bone in a billion is thought to become fossilized. That being so, the legacy of all millions of us with only 206 bones each would be only about 50 bones or one quarter of our skeleton. Since burial can take place within an area of about 3.6 million square miles the odds of being discovered become vanishingly small. Fossils are in every sense very rare. Most of what has lived on the earth may have left no record. There are estimates of less than 1 species in 10,000 having made it to a fossil. The record we have is skewed. Most land animals don't die in sediments. They drop in the open and weather away as they go to nothing. This leaves the fossil record biased in favor of aquatic animals. About 95% of the fossils we possess are from creatures that lived under water.

(via West Seattle Petroglyphs 4/05, via Pebbles 2/05 and excerpted from Bill Bryson's "A Short History of Nearly Everything.")