A lot of work has been done since the 1960's and has been done in interpreting exactly what the series of bands mean, what do they tell us. One of the early efforts was geared toward looking at very old fossils with this type of incremental growth and trying to count how many bands you have in a year to see if the earth's rotation has actually been slowing down. Well, that doesn't work very well. We just still have to take it on the word of the physicists and astronomers that it is slowing down. But we can look at these bands and we can do things like count how much shell material is deposited in year. So we can understand the growth rate of the animal. We can recognize times of reproduction within the year and right here, where the bands are very compressed, this is winter in the Gulf of California when growth slows down almost to a complete halt.

So, this art, if you will, or this science, of interpreting the growth bands is called sclerochronology which is analogous for dendrochronology, which is the interpretation of tree rings. Sclerochronology is very big at the University of Arizona, which is the scientific home, founding home of dendrochronology. This is a very neat aspect of bivalves. This is exactly what we're going to use and what we need to be able to reconstruct the paleontological history. What we're going to do--and I'll explain this in more detail later on--is essentially look at the isotopic composition along this axis of the shell. Because each shell, each skeleton, is essentially a record of the environment in which that particular animal grew.

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