Different elements have different half-lives and as a result, not one single element can be used to date everything.
Carbon 14, for example, has a half-life of about 5,700 years.
(Isochron dating, which relies on multiple rock samples, is an attempt to correct this, but still has underlying assumptions based on 1 and 2 above.) Examples of Problems with Radiometric dating of rocks: Grand Canyon Lava flows: Sedimentary rocks make up the layers of the Grand Canyon and these are not dateable by radiometric dating.
All the canyon layers are ocean bottom sediments, filled with fossils of ocean-dwelling creatures and plants almost a mile high from top to bottom.
It caused massive sedimentary layering and sorting and fossilizing of the creatures buried therein.
This method is used only on metamorphic and igneous rocks – not sedimentary rocks (which are rocks laid down by water – and is where the fossils are primarily found).
Why else do we find marine fossils on the tops of all the major mountain ranges?
An examination of sedimentary rocks worldwide shows a striking consistency with the unimaginably massive Flood that wiped out whole environments.
Tests like these are pseudoscience and should be ignored.
A Summary of the Million Dollar RATE Research Project (Radioisotopes and the Age of The Earth) Introduction: Rocks and fossils do not come with dates on them.