Re: Guano
 

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The earth does can mass though. About 78,000 tons each year.

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This amounts to about a quarter pound of material per square meter per million years. Not enough to do a lot of covering.

I like the erosion answer. Things need to get covered up pretty quick if they are going to become fossils, so it makes sense they would form in low lying areas. Later they may get pushed up into mountains, making the fossils easier to find