by D. Russell Humphreys

Figure 1. Drilling rig for borehole GT-2 at Fenton Hill, New Mexico, USA, which provided the zircons used in the RATE helium project and the feldspar whose argon is the basis for this study.
Photo by Los Alamos National Laboratory

Here I present a new analysis of old (1986) argon retention data from the same borehole that provided helium retention data for the Radioisotopes and the Age of the Earth (RATE) research initiative.1 The deepest part (4.56 km) of the borehole was hot enough to cause more than a 20% loss of radioactivity-generated argon-40 from feldspar in the granitic basement rock, conventionally dated to be 1.5 Ga old. Data and equations from the 1986 article show that at the present temperature (313°C) at that depth, it would take only 5,100 (+3,800/-2,100) years for the feldspar to lose that much argon. This supports the 6,000 (± 2,000) year helium diffusion age that RATE found for zircons in the same borehole.

Old article interprets argon data oddly

In a recent letter to this journal,2 Gary Loechelt, a critic of the RATE helium project, focused my attention on a paper about past temperatures in the borehole (figure 1) that provided the helium data we used. In 1986 the Journal of Geophysical Research published the article,3 by T. Mark Harrison, Paul Morgan, and David D. Blackwell, three geoscientists at three U.S. universities. It was one of three articles I had cited about the temperature issue. Readers can see my detailed review of all three articles in my recent letter replying to Loechelt.4 As I focused on the 1986 article, I saw that it appeared to ignore the heat that a nearby volcano would have provided to the borehole during the alleged one million years (1.04 Ma) since its last ash eruption. Instead, its authors thought (along with Loechelt) that the temperatures in the borehole were relatively low, e.g. at 2.9 km depth falling below 130°C 870 Ma ago and reaching 87°C more than a million years ago. Then only twenty thousand years ago, they claimed, the temperatures rose dramatically, by more than 100°C, up to the high values observed today….

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