Besides the nonsensical and just plain made up “circular” dating system that Doug Batchelor presents, there are two sorts of dating systems you will hear about – real ones... relative and absolute. Sometimes the term “numerical dating” will be used instead of “absolute dating” and I prefer it because people get too confused by the term “absolute” and its usage in science. People tend to think that when science refers to absolute dating, it is insisting it's "absolutely right" or "exactly perfect" – that's not how it's being used. Rather “absolute” in this case means it's referenced to a number (along with its inherent experimental error) rather than referenced to another object. Let me explain:
If I say a Honda Civic costs $23,000 and a Ferrari costs $230,000, I have used an absolute system to express that pricing (you can call the associated rebates, taxes, licenses, etc. the 'error rates' if you like). If I merely state that the Ferrari costs more than the Civic, I have used a relative system to express that pricing. In other words, in the second case I have stated the value of the Ferrari relative to the Honda. I could even state that the Honda costs $207,000 less than the Ferrari or that the Ferrari costs 10 times the Honda and I would still be using a relative pricing system overall.
Similarly, if I tell you that the trilobite fossil is around 500 millions years old and the dinosaur tooth fossil is around 100 million years old, those are absolute dates. If I merely tell you that the trilobite is much older than the dinosaur, that would be expressed using a relative scheme.
Later in the series we'll get into how science has developed absolute dating methods for rock layers and fossils, but for now I'm only going to focus on the older (but still just as valid) 'geological sequencing' or 'geologic succession' method of relative dating. As we learned in our previous installment, consilience from completely different lines of evidence are a powerful way to confirm and strengthen conclusions. Since absolute and relative dating methods are based on completely independent principles, the fact that they agree is strong evidence for the validity of each.
The principles of relative geological dating were developed (or at least formalized) beginning in the 17th century by the early geologists such as Nicholas Steno. The stratigraphic scheme is based on simple, logical, easy to understand geological principles that are for the most part observable and have easily stood the test of investigation, confirmation and time. The relative dating of fossils, or “biostratigraphy” is based substantively on those same principles with additions developed by William Smith in the 1800s (read the excellent book “The Map that Changed the World” to learn of Smith's work).
When biostratigraphy arrived on the scientific scene, the addition of the added and independent biological principles of faunal succession to the established principles of geological succession strengthened both disciplines through the consilience of the evidence. Through methods we will explore in future installments - such as the Index Fossils so undeservedly mocked by Batchelor, geologists were able to put a much finer point on their knowledge of geological history. The understanding of biological history of course benefited as well in a time a full generation before Darwin and Wallace would put forth their independently conceived Theory of Evolution (ToE).
But enough with history for now, let's get on with some basic geological principles of stratigraphy.
To save time and space in this installment I've put together a short (as possible) video. It's not possible to squeeze a freshman geology course into a 30 minute video (if they could, they would), but it's also not possible to understand geology based dating systems without putting in a bit of time and learning effort. If you want to understand how reliable the radiometric dating systems are that we will deal with in a later installment, you have to start with the basics of geology – there's just no shortcut.
I've included some images that came from Google image searches using terms such as “road cut geology” etc. (you can find many more interesting images through your own searches). I also included a few diagrams and animations from a Mr. Sammartano, a science teacher at Hommocks Middle School in Larchmont, New York. This guy does some great public domain work on science topics all around. Look him up on the web.
Geologic Sequencing video: 30 minutes
If you slogged through that, congrats. In order to squeeze that much material into such a short video, compromises and generalizations were made – but I did my best to note when they occurred. When we get to the validity of radiometric dating we will be coming back to these simple relative dating methods to test and confirm how well the numeric dating methods work.
No comments:
Post a Comment