[RightWhale]

It has to be tough to find the oldest evidence. Consider how few fossils of land creatures are found; extraordinary circumstances such as immediate burial by mud or cold water might allow an animal skeleton to be preserved, but almost all the time the carcass is devoured so there is nothing left at all. Nature eats the evidence of its origins.

[gcruse]

"Nature eats the evidence of its origins."

In this case, like the cheshire cat's smile, nature ate but left its apatite behind. ;)

[phantomworker]

Amazing how nature works that way.

Can't wait for the argument,

"Excuse me, teacher, but were you there?"

[ahayes]

Nature eats the evidence of its origins.

True, in the case of these rocks there are not many ancient rocks remaining because so much of the earth's crust has been subducted back into the mantle since the crust first formed.