(reposted from D. Russell Humphreys, "Zircons: God’s Tiny Nuclear Laboratories," published in Creation Matters, a publication of Creation Research Society, Volume 17, Number 3, May/June 2012, to appear at http://www.creationresearch.org/creation_matters/pdf/2012/CM17%2003%20for%20web.pdf)
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This looks like a good time to re-tell the story of zircons and radioactivity since, after seven years of publicity about the RATE project [see reference], there are still some people who haven’t yet appreciated this marvelous evidence for creation. I say “marvelous” because it seems as if God esigned zircons as microscopic nuclear laboratories specifically to show some of the amazing things He did with radioactivity.
How did lead get inside zircon crystals? Evolutionists claim that there was no lead present during the creation of the crystals, and that the lead which is present is a result of radioactive decay of Uranium 238, which has a half-life of 4.46 billion years. They argue that if the earth were only 6,000 years old, there would not be as much lead present in the zircon crystals as is currently found.
Retelling the story
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| When zircons form, they chemically attract uranium atoms and chemically reject lead atoms. Afterward, the uranium decays, depositing both lead and helium within the crystal. |
However, the uranium ions in the molten rock also have a +4 electric charge and four chemical hooks, and they are only about 20% larger than the zirconium ions. So, as a uranium ion floats by a zircon lattice that is forming, the lattice will often reach out (electrostatically), grab the uranium ion, and stick it into the place where a zirconium ion would normally go. As the crystal forms, it will have uranium ions distributed throughout it, often in up to 4% of the normally-zirconium sites. In fact, most of the uranium in crustal granites is concentrated in zircons.
Getting the lead out
But what about the lead ions in the molten rock? It turns out that the most common type of lead ion has only +2 electric charge (only two chemical hooks) and is more than 40% larger than a zirconium ion. (There is another type of lead ion that has +4 charge and is about the same size as a zirconium ion, but at the temperature of the molten rock it is much less common than the first type.) This makes it difficult for the lead +2 ion to fit into the lattice, so the lattice rejects it. Laboratory experiments with zircons forming in lead-enriched molten rock show that the zircons absorb very little of the lead.
Thus, zircons forming naturally will start out containing a lot of uranium and very little lead. Most of the uranium is the most common uranium isotope, uranium 238.
However, it turns out that zircons in pre-Cambrian granites have quite a bit of lead, almost all of it being lead 206, the isotope descended from uranium 238 decay. Relatively little of the lead isotope that is not descended from nuclear decay, lead 204, is in the zircons. (If there are significant
amounts of thorium 232 in the zircon, then significant amounts of its descendant, lead 208, will be there also. Lead 207, the descendant of the relatively scarce uranium 235, is also in zircons in small amounts.)
Zircon is also a very hard crystal with a tight lattice, so once it has solidified, very little uranium and lead can enter or leave it.
Helium for the ages
Lastly, of course, there is the helium produced by uranium decay. It is there in the zircons, in large mounts — consistent with the amount one would expect from the amount of lead 206 in the zircon if it were produced by nuclear decay. Helium atoms, being lightweight, fast-moving, and not chemically sticky, would depart from microscopic zircons in only thousands of years. The fact that helium is STILL THERE is the conundrum for long-agers upon which the RATE project team seized.
It follows that the only answer to the original question (how does lead get into the crystals?) which I can imagine is this: most of the lead — on the order of a billion years’ worth at today's decay rates — got into the zircons by nuclear decay of the uranium 238 that was in the zircons from their beginning. Yet we know from Scripture that there were only thousands of years available for the decay to take place. So billions of years worth of decay took place within thousands of years ... accelerated
nuclear decay! The young helium diffusion ages we got for RATE’s zircons confirm that.
Marko comments: The Bible says that "scoffers will come, and will say, 'everything goes on as it has since the beginning of creation.'" (2 Peter 3:4) Mainstream scientists would say that radioactivity is included here - that the half life decay time of atoms like Uranium 238 has always been 4.46 billion years. This helium evidence from the RATE project shows the contrary, the decay time was much much faster only a few thousand years ago. Wow, this is when the Bible indicates God created the heavens and the earth!
Reference
Humphreys, D.R. 2005. Young helium diffusion age of zircons supports accelerated nuclear decay,
ch. 2 of Radioisotopes and the Age of the Earth, Volume II, Results of a Young-Earth Creationist Research Initiative, L. Vardiman, A. A. Snelling, and E. F. Chaffin, editors, Institute for Creation Research, El Cajon, CA and Creation Research Society, Chino Valley, AZ, pp. 25-100. Archived at:
www.icr.org/i/pdf/technical/Young-Helium-Diffusion-Age-of-Zircons.pdf.
