Application of radioactive dating methods to sedimentary rocks is here considered. The basic assumption that radioactive disintegration starts when the minerals enter the host rocks is shown to be unsubstantiated. Recent research on young rocks discloses that disintegration in them is already at an advanced stage. The conclusion reached is that the theoretical ages calculated from isotope ratios are not the ages of the rocks, or of the earth but are simply ratios of the minerals themselves which originated in the crust of the earth.