Age Correlations and An Old Earth, Version 2 No 1

I'm not sure of the amount of data, but certainly, it is hard to find the oldest pieces of the solar system. The clock starts when the uranium enters the rock as a mineral. Until that mineral forms, there is no clock. And you cannot start a U238 clock with daughter products.We don't date atoms. So, upon forming, a zircon crystal can only take in U238 that exists, not what has already gone down the decay chain.

I'm not certain, but since the half life of K40 is 1/4th that of U238, I'd think there is some overlap. If it was less than a tenth, that might indicate otherwise.I'm certain that other methods do overlap. There are a plethora of them that have cropped up since I studied this subject.

So you are arguing for a "gap" old earth argument, which starts with the creation of "primordial" material and then jumps to modern creation of the earth and life? As I understand it there were several different radiometric methods used. U/Pb was one another was Pb/Pb, for example. These either need to "arrive" via decay over 4.55+ billion years OR the proportions of the isotopes need to be "jiggled" so that they appear to measure the same age.I found Snelling's paper to be more confusing than enlightening on how he thought it worked out, with a lot of extraneous information added that increased the obscuring of his results. How do you think this would work?

Perhaps too pedantic, but the clock can be re-set to zero by sufficient heating. One of the many nice things about zircons is that they have to be heated pretty seriously to do that, 900-1100 C based on a quick Google. Maybe there's a more widely agreed number but any way you slice it it's hot.

So you are arguing for a "gap" old earth argument, which starts with the creation of "primordial" material and then jumps to modern creation of life?How far do you go back? Original hydrogen star formation that then made heavier elements in a universe some 12.7 (iirc) billion years old? Which this thread addresses -- tree rings, lake varves, ice layers all show evidence for an earth older than YEC models and consilience with 14C (and other) radiometric systems. And these "reset" systems are used to date those (volcanic origin) rocks. Uranium decay inside zirconium crystals for instance. Well the age of first life has been set around 3.7 billion years ago by radiometric dating of objective evidence, so this evidence shows life on earth at that point in time, and the earth must have existed before then, and the existence of life would mean it is post primordial yes? Like I said, it allows for gap creationism.Edited by RAZD, : 7

Not exactly. I am asking why such a thing is inconsistent with radiometric dating at constant decay rates and nothing else. Obviously other dating methods pretty much rule out earth being only 10000 years old.But the material of our solar system, at least on an atomic level, was created some before the solar system was formed. I don't know exactly how long. I think you are actually asking my question. If meteor rocks are the same age as the solar system that implies either a reset or a creation from a relatively nearby supernova. Matter and dust doesn't travel between stars at the speed of light does it? That would not have any effect on the answer. We all agree that the meteor is 4.55 billion years old in at least some sense.Edited by NoNukes, : No reason given.

It should always be remembered that, one way or another, what we see are cooling dates when working with magmatic rocks.However, since Pb is relatively immobile, these dates are not as susceptible to resetting as would Ar. Partial melting would be a disaster in some cases.

Yes, K40 dates do overlap with U238. I had not considered them. But do they address the problem? Do we have any 4 billion year old K40 dates that we know were set to zero on earth?

From Geological Time I see:

Parent	Daughter	Half Life (years)	Dating Range (years)	Minerals/materials
Uranium-238	Lead-206	4,500 million	10-4,600 million	Zircon, Uraninite.
Potassium-40	Argon-40	1,300 million	0.05 to 4,600 million	Muscovite, Biotite, volcanic rocks.
Rubidium-87	Strontium-87	47,000 million	10-4,600 million	Muscovite, Biotite, Metamorphic or Igneous rocks.

(actually K40 in the Ar-Ar method has been used to date the eruption of Vesuvius 76 AD, or about 0.002 mya, somewhat of a tour de force). And I'm pretty sure that other isotopes such as Samarium are also comparable. One could also dive into Dalrymple and look at TABLE 4.1 Radiometric Ages of Some Early Archean and Related Rocks of the North Atlantic Craton to see how they do overlap and agree. (Note that in each of the two parts of the table the units are listed in stratigraphic order so you can see the close correlation to that).Side note: Wherever you have some U238 you also have some U237 and you measure the Pb206 and Pb208 and get two largely independent dates. If they agree they are "concordant" and pretty solidly established. If they disagree they are "discordant" and a pretty solid age may be establishable. Nobody call this "U238 dating".

My understanding is that the clock is "set" when the small particles of matter from older novae accumulates into larger balls of matter so that the parent\daughter material share the same location. One of the problems with the lead dating (see cosmos ?) was contamination by lead from other sources (which would include "primordial" lead from older decay not associated by location with the parent).Edited by RAZD, : ..qs

As do many others. Ther are lots of dating methods.The oldest claimed date I know of for such is 4.28bya, Neodymium-142 Evidence for Hadean Mafic Crust (free registration required). The abstract:

quote:

---

Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142Nd/144Nd ratios than the terrestrial standard (ϵ142Nd = —0.07 to —0.15). Within a mafic amphibolite unit, 142Nd/144Nd ratios correlate positively with Sm/Nd ratios and produce a 146Sm-142Nd isochron with an age of 4280⁺⁵³_-81 million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.

---

The Acasta gneiss near Great Slave Lake in north central Canada is purty darn well established at 4.03 bya, e.g. Age of the world's oldest rocks refined using Canada's SHRIMP: the Acasta gneiss complex, Northwest Territories, Canada.

There were 10 different methods listed on the graph, and presumably these would work equally well on earth rocks. Yes the major problem with dating the earth directly is finding an outcropping of old rock.

Thanks JonF. I think you, NosyNed, edge, and RAZD guys have addressed my question quite completely.

quote:

---

Nobody call this "U238 dating".

---

Correct. That is why I referred to it as a U238 'clock'. I figure that gives me more poetic license.

I don't understand this particular point. Did you mean U235 rather than U237? At a time when U238 is getting incorporated into a mineral there should not be any amount of U237 around, should there?