\doc\web\99\12\geoform.txt From: "Will Pratt" To: Subject: Re: Dating footnotes Date sent: Wed, 25 Aug 1999 16:20:54 -0700 arthurhu@halcyon.com wrote in message <7q1q73$hoo$1@nnrp1.deja.com>... >You know, the one thing I have not found is >any consistent footnotes explaining how most >of what you find in science textbooks was >dated. How did they know such and such fossil, >dinosaur, or trilobite was so many million >years old? Are there detailed references on >the net or do you have to go through research >hell to find out this stuff?? [snip] Try this url: http://www.talkorigins.org/faqs/isochron-dating.html It discusses the dating methods used and provides references for futher reading. In general, one does not date the individual fossil, but the formation thay occur in. For the very general ages needed by textbooks and such, though, there are tables of known absolute ages correlated with geological periods. So that if you know that a fossil is, e.g., from the upper Permian, many dates have been correlated to show that upper Permian formations range from 240 to 230 mya, so a "ballpark figure adequate for most uses would be "ca 235 mya". For closer dating you would check for more detailed tables. For example, if you had a fossil from the Lamar Limestone of the Guadalupe-Delaware Mtns region in Texas, you might find that the age of the formation is "ca 242 mya" and could give a more exact age. For sedimentary sequences less important economically than the Permian Basin, the ages might be more widely spaced, but today we have a fairly good chronology accumulated for most of the reasonably well studied sequences Will -- William L. Pratt, Ph.D., Curator of Invertebrates, Barrick Museum Mail Stop 4012, Univ. Nevada, Las Vegas 89154-4012 (702) 895-1403; Fax (702) 895-3094; prattw@nevada.edu thanks, that helps. I was wondering how you can date sediment if the only thing you can date are newly created rocks, and the only new rocks after the crust hardens are volcanics. So you'd have to trust the geological tables which is based on a lot of dates and sleuthing. Unfortunately, that's not good enough for our doubting Thomases. From: "Will Pratt" To: Subject: RE: Dating footnotesfor, say the Date sent: Thu, 26 Aug 1999 11:23:17 -0700 > > -----Original Message----- > > From: arthur hu [mailto:arthurhu@halcyon.com] > > Sent: Thursday, August 26, 1999 9:57 AM > > To: Will Pratt > > Subject: Re: Dating footnotes > > > > It should be noted that you can't expect freshman level texts (let alone > high school) to footnote sources of figures or information. Or at least, > they don't do so. This is as true of Biblical studies as geology or biology. > > The first thing you are really going to need for this project is access to a > fairly good university library, or else a Interlibrary Loan through your > local beanch and a _lot_ of patience. > > > This is to convince the creationists, so I how I tell them you > > figure out the tables for the various fossil formations? isochron > > dating? > > The relative chronology of geological strata has been worked out by > historical geologists using methods developed, in priciple, during the early > 19th century. For example, in an undeformed series of sediments formation A > is above formation B, therefore B is older than A. The subject is > "Historical Geology". > > Isochron dating is applied to igneous and plutonic rocks, for the most part. > Formation A is found in location 1 between layers of volcanics dated as 85 > mya and 87 mya, therefore at this location formation A is between 85 mya and > 87 mya. At location 2, formation A lies conformably on top of formation B > which has been dated by other studies as extending upward to 86.7 mya, and A > is intruded by vocanic dikes dated as 83.6 mya. Now a formation must have > been already formed to be intruded, therefore we can now say that formation > A was deposited before dates of 85 mya and 83.6 mya. And so on, for many > localities and dates applying various restrictions until eventually we can > state that the lower limit of formation A is at 86.7 mya, conformably on > formation B, and it's upper limit is greater than 85.2 mya, which has been > established as the age of the lowermost layers of formation C, which is next > above formation A, but is separated by an uncomformity in all known > sections. > > You need to read texts dealing with historical geology methods and isocron > dating for this. > > > If so, where are the footnotes that gave the exact > > location of samples, and what type of dating was used, and the > > data, > > In the primary literature, that is, articles in research journals. You'd do > well to read a few to get an idea, but bear in mind that the primary > literature of any field requires a lot of background information to > understand. In review volumes "_Annual review of xyz_" you will find the > information summarized and expressed in the technical language of the field > as a whole, with the terminology of particular branches explained. It is in > such volumes that someone will collect all the available dates and correlate > them into a table, which someone like Raup and Stanley, 1971, _Principles of > Paleontology_ will publish as figure 11-17 of their textbook. > > > or how easily is this replicated in a high school lab? > > Can you go in your back yard, find an old strata layer, and > > date it? > > If you mean isochron dating, you can't duplicate it in a high school lab at > all. Too much equipment needed, which sells for prices orders of magnatude > above even the most generous high school budget. Researchers don't do their > own dating, they send it to the relatively few labs which do isochron > dating, at prices around $500 a date (very roughly, and radiocarbon is > cheaper, maybe $250 per). > > If your area has been mapped, and your back yard is severely eroded, you may > be able to actually collect samples and identify the formation using the > literature ("Geology of such and so county") and in particular the > geoloigcal maps showing surface formations. You can then translate > formation name, e.g. uppermost Pierre shale (in Kansas or Nebraska) to > standard stage (lowermost Maastrichtian), and from the table in Raup and > Stanley find that the lowermost Maastrichtian is 72 my old. > > Will > > -- From: "Will Pratt" To: Subject: RE: Dating footnotesfor, say the Date sent: Thu, 26 Aug 1999 16:12:00 -0700 > > So once you establish a trilobite is in cambrian strata, that pretty > much dates it assuming somebody else dated the cambrian layer. > > So who dated the cambrian layer first? In general terms, many different researchers, for many different formations within the Cambrian. It extends from 600 mya to 500 mya. To find out who made the first dating you'd have to go to books on Cambrian sediments, fossils, etc., and probably from there to the primary literature. But any good review volume will provide extensive references to the original papers in which the results were first published. You have a problem with the extreme creationist in that they have no background science to build on, and also have the idea that "The Truth" should be clear to "the ordinary joe". The fact that Civil Engineering and Automobile Repairs aren't either doesn't seem to signify. There's an overlapping problem in that the vast majority of YECs are also anti-intellectual: they tend to be almost as truculent towards Theologians as they are towards Biologists. And they insist upon absolutes, "THE Truth", "THE moral system", etc. They have enormous trouble with relative values. There are a lot of people, though, who simply haven't been exposed to factual information. If you can sneak around and get to those when they're ready to listen. . . Will -- William L. Pratt, Ph.D., Curator of Invertebrates, Barrick Museum Mail Stop 4012, Univ. Nevada, Las Vegas 89154-4012 (702) 895-1403; Fax (702) 895-3094; prattw@nevada.edu