Reflectorites
In view of the recent debate over radiometric dating, the following October 1999
SCIENCE article might be of interest
It claims that radioactive dates may be out by "a percent or so", because different
chemical forms of radioactive elements decay at slightly different rates.
It hastens to add that "Creationists hoping to trim geologic history to
biblical proportions will be disappointed-the variations seen so far are much
too small..."
But as the article points out: "If similar effects turn up in other radioactive
clocks that tick over hundreds of millions or even billions of years,
however they would loom large to geochronologists trying to work out the
order of closely spaced geologic events in the distant past."
As the effect cited seems to increase the rate of decay, and evolutionists
are already being squeezed for time in the origin of life and the Cambrian
Explosion, if it turns out that they have "a percent or so" less time than
originally thought, they will be even more squeezed!
Steve
======================================================================
[...]
Tweaking the Clock of Radioactive Decay
Certainty, it seems, is on the wane. The sun may rise tomorrow on
schedule, and the sea sons may pass as they always have. But radioactive
decay-the pacemaker of geologic time-can no longer be called precisely
"clocklike." Says geochemist Douglas Hammond of the University of
Southern California (USC) in Los Angeles: Everybody always assumes
radioactive decay to be totally independent of temperature, pressure, and
chemical Some it seems there are some exceptions."
---Atomic cannibals Beryllium-7 decays by capturing one of its own electrons, transforming a proton into a neutron. because chemical bonds affect the electron's behavior, the decay rate of beryllium-7 can depend on its chemical form.---In the 15 September issue of Earth and Planetary Science Letters, geochemist Chih-An Huh of the Institute of Earth Sciences of the Academia Sinica in Taipei reports that the decay rate of beryllium-7 varies, depending on its chemical form. Creationists hoping to trim geologic history to biblical proportions will be disappointed-the variations seen so far are much too small, just a percent or so, to affect Earth's overall time scale. Still, the variability in beryllium decay will prompt those who want to trace out fine divisions in the earliest reaches of time to take a close look at their pacemakers.
Theoreticians long ago anticipated some variability of radioactive decay. The decay of beryllium-7, for example, should depend on the density of electrons at the nucleus. That's because it transforms itself into lithium-7 by capturing one of its own electrons, turning one of its protons into a neutron, and emitting a gamma ray. When a change in chemical bonding subtly rearranges the electrons and increases an electron's chance of finding itself at the nucleus, the odds are better that it will be captured and the beryllium will decay.
In the last few years, German researchers have demonstrated the converse of this effect: a surge in the decay of rhenium-187, which emits an electron rather than capturing one. When Fritz Bosch and his colleagues at the Gesellschaft fur Schwerionenforschung in Darmstadt, Germany, stripped away all the electrons from rhenium nuclei, something that might happen in a star's harsh interior, its half-life plummeted from 42 billion years to 33 years. But, until now, researchers have detected only tiny variations (or none at all) in the decay rate of beryllium and other atoms under Earth-like conditions.
Undismayed, Huh applied the latest technology to the problem. He used an extremely sensitive but stable gamma ray spectrometer to monitor the decay of beryllium-7 (which has a half-life of about 53.3 days) in the form of the hydrated ion, the hydroxide, and the oxide-chemical combinations common in the environment. Thanks to an unprecedented precision of i0.01%, he could see that the half-lives of the three forms were 53.69 days, 53.42 days, and 54.23 days, respectively. The 1.5% range is "probably quite real," says geochemist Teh-Lung Ku of USC. "Although the idea has been around quite a while, this time [the researchers] will be able to show it more convincingly."
It remains to be seen how important the effect will be in dating geologic samples. Beryllium-7 is used to gauge the rate of erosion or sediment deposition over weeks to months. Except perhaps in studies aspiring to the highest possible resolution, the decay variability due to chemical form is likely to be swamped by other uncertainties, says Hammond.
If similar effects turn up in other radioactive clocks that tick over hundreds of millions or even billions of years, however they would loom large to geochronologists trying to work out the order of closely spaced geologic events in the distant past. Such fine distinctions matter, for example to researchers who are using the decay of potassium-40 (half-life of 1.25 billion years) to sort out the mass extinction of 250 million years ago (Science, 15 May 1998, p. 1007). But, although potassium-40, like beryllium-7, decays by electron capture, its innermost electrons-the ones most likely to be snagged-are more strongly shielded from external effects. The potassium ion has two complete shells of electrons protecting its two innermost electrons, whereas the beryllium ion has none. Thus, researchers expect the effect of chemical form on potassium-40 to be far less than on beryllium-7.
But that won't stop Huh from trying to check the constancy of this clock. Even now he is counting decay rates of rubidium-83. It has an electronic structure that provides even more shielding than does potassium-40, but its 86-day half-life will make experiments reasonably quick to perform. In a few months, he'll know if ancient days are even a tiny bit closer than we thought. - RICHARD A. KERR
[...]
(Kerr R.A., "Tweaking the Clock of Radioactive Decay", Science, Vol. 286, 29 October 1999, pp882-883)======================================================================
--------------------------------------------------------------------"The principal problem is morphological stasis. A theory is only as good as its predictions, and conventional neo-Darwinism, which claims to be a comprehensive explanation of evolutionary process, has failed to predict the widespread long-term morphological stasis now recognized as one of the most striking aspects of the fossil record." (Williamson, Peter G. [Assistant Professor of Geology, Harvard University], "Morphological stasis and developmental constraint: real problems for neo-Darwinism", Nature, Vol. 294, 19 November 1981, p214) Stephen E. Jones | sejones@iinet.net.au | http://www.iinet.net.au/~sejones--------------------------------------------------------------------
This archive was generated by hypermail 2b29 : Thu Mar 02 2000 - 08:03:53 EST