English to Spanish Science Archaeology A religious book about the Creation/evolution debate

The next scheme that is often quoted is the uranium-lead dating method. This method is similar to the potassium-argon method although there are two isotopes of uranium which can be used (uranium 238 -> lead 206 and uranium 235 -> lead 207) and a similar thorium 232 -> lead 208 method is also employed. To use any of these methods, as before, the logarithmic decay rate must be ascertained, it must be established that the decay rate is not changed by pressure, temperature changes and the original concentrations of uranium/lead, thorium/lead must be known. By examination of ***halo marks*** left by this sort of radioactivity, it has been shown that the decay rates of the uranium—thorium—lead decay sequences are in fact not constant.