Dating by Stratigraphic Position

Excellent topic, jar!Of course, this is one of the methods by which Christian geologists realized that earth was hundreds of millions of years old, at least.If no true creationist decides to argue with you on this, I may try to play devil's advocate.

My guess is that there would be a lot of wear on the fossil. It is now a rock, and rocks wear a lot as they are transported. Bones are not worn, at least not like rocks. So if a fossil shows definite signs of wear, it can probably be concluded that it was transported or weathered or something after fossilization.

We expect layers to be horizontal. If they are not, then we could probably conclude that something has disturbed them after the lithified. In fact, by tracing the layers over a large area we can sometimes trace out that the layers have been pushed together to give a folded appearance.We can also check to see if the minerals in the rocks are the type to have been formed under heat and pressure - metamorphic rocks, for those in the know.

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Actually, not in all cases, but for a first approximation this is okay.

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Hi, edge.Yeah, I thought the intent of this thread was to start with a simple model of statigraphy, ala Steno, and then add complexities as we go along. Notice that I didn't mention the use of index fossils to correlate layers.And I knew we wouldn't expect all "layers" to be horizontal, but I couldn't think of an example. But your posts reminded me of one: alluvial fans!

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How big an area are these layers? Do they cross major divisions like an ocean?

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Some do - for a period in time (actually there were at least two periods) all the continents were joined together, so the continents were connected together.

Interesting question, Ned. What do we mean by "correlation"? I guess I'm thinking in terms of 18th century (pre-Darwin!) geology (practiced by Christians!). Certain fossils always occurred in the same order in the stratigraphic record, no matter which country you were looking at. It came to be realized that what they were seeing is that very distinctive life existed at different epochs in earth's history. It was then hypothesized that if you saw the same fossils in two strata in two widely separated places, those strata were laid down at the same time. (This hypothesis was confirmed, of course, by radiometric dating.)To answer a very much earlier question, Ned, I would say that since organic bone is a very different material than a mineralized fossil, it should be easy to tell whether a fossil was eroded out of the original material and transported after fossilization. But, then, I am not a geologist.