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Geologists have uncovered a great mystery in granite rocks. They find tiny black circles, known as radiohalos. They were caused by radioactive decay of polonium, but the source has disappeared. Where did it come from, and where did it go? The only answer is a global Flood.
Part one of this three-part series described the mysterious “halos” found inside granite (the common speckled rocks used for kitchen countertops and tombstones). These microscopic halos look a lot like “bullet holes.” Why are they of interest to creationists?
Once you learn more about these features, you will see why they mystify geologists. They are hard to explain if granite formed slowly over millions of years, but they make perfect sense if molten material rose near the earth’s surface during the worldwide Flood and quickly hardened into granite.
But first, you will need to understand a bit more about radioactive decay and its effects on rocks.
Geologists have a clear understanding of the radioactive decay of uranium atoms and the decay’s effects on surrounding rocks. We can observe this process today. It is not a mystery.
As explained in the first article, the nuclei of uranium atoms are so large that they are very unstable. As the atoms decay, subatomic alpha particles fly out like bullets, damaging the surrounding material. These bullets produce spherical halos called radiohalos (an abbreviation for “radioactive halos”).
After the first set of these particles is ejected, the smaller nucleus is still unstable. So more particles are ejected from the nucleus. This happens repeatedly until the atom is stable and no longer decays. In what is known as the uranium decay chain, the nucleus of the original uranium-238 atom typically undergoes eight alpha-particle changes until it becomes the stable lead-206 atom (see “The Uranium Decay Chain—The Source of Radiohalos” below).
All the intermediate steps during the radioactive decay of uranium-238 are shown, resulting in the final, stable element lead-206. Where the arrows point downward, those changes result from alpha decay. The arrows pointing upward indicate beta decay. (Alpha decay involves the loss of two protons and two neutrons; beta decay involves splitting of a neutron, the loss of an electron, and the gain of a proton.)
The original (or parent) uranium nucleus contains 92 protons. That’s why uranium is element number 92 on the periodic chart. However, after two protons are ejected in an alpha particle, the nucleus then has only 90 protons, so the uranium has changed into element number 90, which is thorium.
The nucleus of thorium is still unstable, so it decays radioactively. However, it decays by successively splitting and ejecting two electrons, known as beta particles, while gaining two extra protons, giving it a total of 92 again. So the thorium has changed back into the element number 92, uranium.
But this uranium is now four neutrons lighter. Whereas the original parent uranium atom had 146 neutrons and 92 protons in its nucleus (called uranium-238), this uranium atom has only 142 neutrons and 92 protons (called uranium-234).
The nucleus of this uranium-234 atom is still unstable, so it decays. The process continues through what is known as the uranium decay chain, until the stable lead-206 atom is reached, the final end product.
The picture is a little more complicated at the bottom end of this decay chain. At polonium-218 there is “branching,” but most polonium-218 atoms decay to lead-214. Then they quickly decay to bismuth-214, then polonium-214. The main decay path is depicted with solid red arrows. And the main eight alpha-decaying atoms are shown in red.
Figure 1 shows a sample radiohalo that resulted from this process. Notice the eight dark rings. Why eight and not just one? As each of the alphaparticles is “fired” from the nucleus, it has a different energy. Consequently each bullet travels a different distance into the surrounding material before it stops to leave a black mark.
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