Will radiohalos in coalified wood upset geological clocks?
In some coalified wood, uranium-rich solutions have deposited radioactive particles that subsequently decay and create little rings (halos) that can be seen under high magnification. The ra-dii of the rings depend upon the energies of the particles emitted by the radioactive elements. Each type of radioactive decay has a specific half-life. Thus, the patterns of radiohalos help measure the age of coalified wood. A challenge to geology arises because the radiohalos in coalified wood from Jurassic and Triassic formations, supposedly millions of years old, suggest ages of only a few thousand years.
(Connor, Steven J.; "Radiohalos in Coalified Wood: New Evidence for a Young Earth," Creation Research Society Quarterly, 14:101, 1977.)