I further revised my essay on November 24, 2005 to reply to Humphreys (2005a) and again on July 25, 2006 in response to Humphreys (2006).
Here we conduct thermal and room temperature alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California.
However, the ability of zircons to record accurately the geomagnetic field has not been fully demonstrated.
Paleomagnetic experiments on ancient zircons may potentially constrain the earliest geodynamo, which holds broad implications for the early Earth interior and atmosphere.
Walsworth Zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration.
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[Original version: March 17, 2005] [Revisions: November 24, 2005; July 25, 2006 and June 20, 2010] The following material may be distributed as long as the author is acknowledged, the material is not sold and the text and its internet links are not altered or edited. Humphreys has not silenced his critics, we are waiting for him to answer our numerous questions.
Talkorigins permanently archived the original version of this essay after the first update on November 24, 2005 contrary to erroneous statements in footnote #25 of Humphreys (2008b).
We further conclude that a combination of quantum diamond magnetometry and high-resolution imaging can provide detailed, direct characterization of the ferromagnetic mineralogy of geological samples.
As such, while zircons can reliably record the geomagnetic field, robust zircon-derived paleomagnetic results require careful characterization of the ferromagnetic carrier and demonstration of their occurrence in primary inclusions.