Representative index fossils |
Before we go any farther, we'll answer the question: Fossil correlation is the use of the fossils found within and adjacent to a rock unit of unknown age to assign it a relative age. That's the basic, Historical Geology 100 meaning of "fossil correlation." That's twenty-five words, and you can find something to that effect buried within the 350-plus words Woodhouse published in her post. Where she went all bonkers is in the padding, padding that included such bogosity as
- "Usually only part of an organism becomes a fossil after the organism dies. This tends to consist of bones and teeth, rather than soft tissue."
- "Fossil correlation relies on geologists knowing the ages of certain planets [sic] and animals."
- "Index fossils must be found in a large number of areas, but only in a limited thickness of strata."
- "Ammonites are the best-known index fossils."
- It's not "bones and teeth," Emma, it's "hard parts." The vast majority of known fossils preserve the shells of animals, not their bones. That's because they didn't have bones.
- We suspect you meant "plants." And we would also like to point out that paleontologists know the ages of many, many, many plants and animals; not just "certain" ones.
- Instead of "limited thickness of strata," the definition of an index fossil includes a (relatively) brief lifespan. We know this is hard to understand, Emma; but "thickness of strata" is not the same as length of time, because rates of deposition vary widely.
- No, ammonites are a good example of an index fossil, but only in the Mesozoic (see image above). Other floating animals are useful in Paleozoic rocks, before the "explosion" of ammonites; and Cenozoic rocks, when they are extinct. Oh, and ammonites didn't have either bones or teeth...
¹ eHow.com isn't gone, it's just jumped on the "niche-site" bandwagon, parceling out much of its content into sites that are (supposedly) about a relatively narrow topic. Unfortunately, they didn't correct most of it...
² DMS = Demand Media Studios, parent company of eHow, now called Leaf Group. We always like to say that you can't spell "dumbass" without "DMS."
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SI - PALEONTOLOGY
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