Young-Earth creationists are forced to claim that the overwhelming majority of fossils that appear to have been preserved in life position were actually not formed that way; they only appear to have been, as a serendipitous result of the vicissitudes of catastrophic burial during Noah’s Flood. That is a remarkable burden to bear.
At the onset of the flood (one can only imagine, since there are no natural mechanisms with which to work), organisms in life position would have been scoured and picked up by the catastrophe in order to populate all the sediments that were created and subsequently deposited by the flood. (Presumably sediments that might have existed prior to the flood would have been devoid of fossils.) Any organic remains deposited during the flood could not be in life position, since the rate of sedimentary accumulation needed to satisfy the creationist claim that the vast majority of global sediments were laid down in one year is vastly too rapid for organisms to establish themselves in life position.
For Noah’s Flood to have resulted in the formation of the fossil record, the only fossils that could be in life position would be those on the very bottom of the pile, or those at the very top, which would have reestablished themselves following the Deluge. (Creationists have not identified any such layers.) However, if you find just one fossil in life position (and all it takes is one) within a pile of sedimentary rock, what you then know is that the rate of sedimentation was slow enough (or no sediments were being deposited) so as not to interfere with that sessile organism for however long it lived at that level within the strata.
Seeing fossils like the oysters I’ve described preserved in life position is a very simple yet powerful way to refute the claim made by young-Earth creationists that the fossil record is the result of a global Noah’s Flood. What these fossils prove instead is that there must have been a period of time, at a minimum equal to the age of the oyster reef, during which sedimentation rates were very low. That period of time during which those oysters were living in this one place far exceeds the total duration of Noah’s Flood as described by young-Earth creationists. Add to the age of the reef the age of all the other fossils in the cliffs that are found in life position and one quickly realizes that the Earth must be much much older than 6,000 years.
You too can know that the Earth is ancient just by knowing about fossils in life position, without having to understand the technical aspects of radiometric dating. (And, by the way, creationists should actually not acknowledge the existence of fossils at all, since by definition a fossil has to be at least 10,000 years old. Whenever creationists refer to fossils, they do so by changing the definition of the word, since according to them Noah’s Flood happened only about 5,000 years ago.)
But an ancient Earth doesn’t “disprove” the Bible. Descriptions of nature and the “cosmos” in the Bible were adequate at that time to make the spiritual points, if any, for which they were called into service. However, biblical cosmology is no longer adequate today if taken to stand on its own, divorced from its contextual origin. Some would argue that because the cosmology of the Bible is out of date, so too is its spiritual validity. Its cosmology roots the composition of the Bible in a time and place; so yes, it is out of date in its descriptions of the Universe. But I don’t know that justice, mercy, forgiveness, hope, and love have been replaced with something better. An emphasis on these could not wait until humans had figured out the exact nature of reality (we’d still be waiting). The Bible never makes the claim that its descriptions of the physical universe are good for all peoples for all time, whereas it does make certain pronouncements about being a guide to whoever has an interest in being right with God.
Dr. L. Ward (Virginia Museum of Natural History) provided great assistance with some of the geological features described in this series of posts.