New radiohalo find challenges primordial granite claim
Figure 1. A 218 Po radiohalo (from Gentry).18
Although radiohalos are tiny, they have generated a big debate about Genesis, geology and granite. Radiohalos were first brought such prominence when Robert Gentry, the world’s leading researcher on halos, claimed they were evidence of an instantaneous, supernatural creation of granite.1 They were launched into international distinction when Gentry testified to this claim at the Arkansas Creation Trial in 1982.2 And they are still the cause of controversy with books, articles and web pages devoted to the pros and cons of Gentry’s original arguments.3,4,5,6
Now a new find of polonium radiohalos has major implications for the interpretation of their origin.7
Radiohalos are concentric, discoloured circles observed under the microscope in translucent minerals such as biotite, muscovite, fluorite and diamond (Figure 1).2,8 It is generally accepted that they were formed by the alpha decay of radioactive isotopes (Figure 2). The emitted alpha particles damage the mineral, especially at the end of their path when they finally run out of energy and grab electrons from nearby atoms. They leave a spherical, discoloured region, which in section appears circular. Radiohalos can be erased when the host mineral is heated, even at temperatures as low as 250°C.9
Gentry describes four types of radiohalos, each with a different number of concentric rings (Figure 2).10 They have been related to the 238U decay series (Table 1) in which eight of the isotopes in the series liberate alpha particles when they decay. Each of the four types of radiohalos has been linked to a specific parent isotope in the series. The single-ringed halo corresponds to 210Po, the two-ringed halo to 214Po, the three-ringed halo to 218Po, and the eight-ringed halo to 238U. A few of the decay steps have similar energy and produce rings close together. These may not be easily distinguished.
Each alpha particle has a characteristic energy that determines the distance it will travel—hence the spherical shape. Thus, the diameter of each ring can be related to the decay of a specific parent isotope depending on the host mineral.11 The shorter the half-life, the greater the decay energy, hence the larger the halo.
Although the uranium isotope has a very long half-life of 4.5 billion years, all the polonium isotopes have short half-lives, ranging from 138.4 days for 210Po, to 164 microseconds for 214Po.
Polonium halos have been found abundantly in granites, and minerals from some 22 localities have so far been reported to contain polonium radiohalos.3 Because polonium isotopes have very short half-lives, it has been argued that ‘granites with Po halos, regardless of their “geological age” are primordial rocks’, created supernaturally and instantaneously during the Creation week. Indeed it has been contended that such granites cannot be duplicated by natural processes.12
This conclusion has been disputed because of the geological relationships of the rocks in which polonium halos have been found.3,4,5 For example, some samples containing radiohalos were from dikes cross-cutting host rocks which thus must be older.4 Rather than primordial, it has been suggested that the parent material of the radiohalo was part of a conventional uranium or thorium decay series segregated by some geological process.
Stone Mountain granite halos
This Journal of Creation reports that abundant radiohalos have been found in biotite flakes from granite from Stone Mountain, USA.7 The significance of this find is that the Stone Mountain granite has been interpreted to have formed not during Creation Week, but during the Flood.
Stone Mountain is located about 30 km east of Atlanta, Georgia and some 200 km south of the southern end of the Appalachian Mountains. Grant describes Stone Mountain as an isolated granitic monolith rising some 238 m above the surrounding countryside.13,14 The granite intrudes both concordantly and discordantly into the country rock, which is composed primarily of biotite-plagioclase gneiss. The country rock was regionally metamorphosed to above the sillimanite isograde. At the granite contact, there is some evidence of contact metamorphism. Contact and structural data indicate that the granitic intrusion was late metamorphic and linked with the regional deformation associated with the uplift of the Southern Appalachians. The granite contains abundant xenoliths of the country rock.
McQueen places the orogony that built the Appalachians at ‘Phase III’ of the Flood, which starts as the floodwaters began to decrease. In other words the beginning of Recessive stage of the Flood.15,16 Froede also ties the regional deformation to the Flood, linking the source magma for Stone Mountain with a ‘Flood generated orogenic event’.17
The halos were well-defined circles consisting of a single ring 19.2 Âµm in diameter. No radiohalos had more than one ring. The radiocenters of these halos were so tiny as to be virtually impossible to see. The observed ring diameter corresponds to the alpha-decay of 210Po.11
It could be argued that the presence of a single ring does not necessarily mean 210Po was the original parent isotope, because all four types of radiohalos (Figure 2) have the 210Po ring. The 210Po rings are very faint, and some other isotopes may have been present, decaying and producing alpha particles. There may not have been sufficient radioactive material to produce a ring dark enough to be seen.
|Isotope||Decay||Half Life||Energy (MeV)|
|238U||Alpha||4.5 billion years||4.19|
|234U||Alpha||0.245 million years||4.77|
| Table 1. The 238U decay series
(Summarized from Gentry and CCNR).2,20
On the other hand, some higher energy alpha decays may have occurred, producing rings larger and fainter than the 210Po ring. There may simply have been insufficient radioactive material to produce larger, visible rings. Thus 214Po and 218Po cannot be definitely eliminated as possible parent material.
No matter which of the polonium isotopes comprised the original parent material, the decay half-life in all cases is very short and raises the question of how the ring could have formed in such a quick time period.
The field evidence points to Stone Mountain being formed during the Recessive stage of the Flood toward the end of a major mountain building episode. This orogeny metamorphosed the Flood-deposited country rock, and uplifted the Southern Appalachians. If this interpretation is correct, the granite was not formed during the Creation Week and the polonium halos cannot be primordial. Nevertheless, the polonium halos show clearly that the parent radioactive material was incorporated into the host rock by very rapid geologic processes.
This new report of polonium halos in Stone Mountain granite is most significant for models of granite formation, and for classification of rocks within the Creation and Flood framework.
References and notes
- See for example, Gentry, R.V., Radioactive halos: implications for Creation; in: Walsh, R.E. (Ed.), The First International Conference on Creationism , Creation Science Fellowship, Pittsburgh, Vol. 2, pp. 89–112, 1986. Return to text.
- Gentry, R.V., Creation’s Tiny Mystery, Earth Science Associates, Knoxville, pp. 111–137, 1988. Return to text.
- Wise, K.P., Radioactive halos: geological concerns, Creation Research Society Quarterly 25(4):171–176, 1989. Return to text.
- Wakefield, R. and Wilkerson, G., Geologic setting of polonium radiohalos; in: Walsh, R.E. (Ed.), The Second International Conference on Creationism, Creation Science Fellowship, Pittsburgh, Vol. 2, pp. 329–344, 1990. Return to text.
- Wise, K.P., Radiohalos in diamonds, Letters to the editor, J. Creation 12(3):285–286, 1998. See replies by Armitage (pp. 286–287) and Gentry (pp. 287–290). Return to text.
- Snelling, A.A., Radiohalos; in: Vardiman, L., and Chaffin, E.F., (Eds), Radioisotopes and the Age of the Earth: A Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, and Creation Research Society, St. Joseph, pp. 381–468, 2000. Return to text.
- Armitage, M., New record of polonium radiohalos, Stone Mountain granite, Georgia (USA), J. Creation 15(1):86–88, 2001. Return to text.
- Armitage, M., Internal radiohalos in a diamond, J. Creation 9(1):93–101, 1995. Return to text.
- Armitage, M. and Back, E., The thermal erasure of radiohalos in biotite, J. Creation 8(2):212–222, 1994. Return to text.
- Gentry, Ref. 2, p. 278. Return to text.
- See for example, Gentry, Ref. 2, p. 241. Return to text.
- See for example, Gentry, Ref. 2, p. 326. Return to text.
- Grant, W.H., Structural and petrologic features of the Stone Mountain granite pluton, Georgia; in: Neathery, T.L. (Ed.), Centennial Field Guide Volume 6, Southeastern Section of the Geological Society of America, pp. 285–290, 1986. Return to text.
- Grant, W.H., Field excursion, Stone Mountain—Lithonia District, Georgia, Geologic Survey Guidebook 2, Atlanta, 1962. Return to text.
- McQueen, D.R., The Southern Appalachian Mountains: An example of 6,000 years of Earth history; in: Walsh, R.E. (Ed.), The First International Conference on Creationism, Creation Science Fellowship, Pittsburgh, Vol. 2, pp. 245–250, 1986. Return to text.
- Walker, T.B., A biblical geologic model; in: Walsh, R.E. (Ed.), The Third International Conference on Creationism, Creation Science Fellowship, Pittsburgh, pp. 581–592, 1994. Return to text.
- Froede, Jr, C.R., Stone Mountain Georgia: a creationist geologist’s perspective, Creation Research Society Quarterly 31(4):214–224, 1995. Return to text.
- Gentry, Ref. 2, p. 213. Return to text.
- Gentry, Ref. 2, p. 278. Return to text.
- CCNR, Here is the decay chain of uranium-238, ccnr.org, accessed February 2000. Return to text.