The Earth itself is known to be about 4.6 billion years old. Perhaps the question is better put, what is the oldest material presently exposed on the Earth's surface? The oldest DATED rock (using uranium-lead isotopic dating on the mineral zircon) is the Acasta Gneiss in the Slave Craton of Canada's Northwest Territories. It is dated at 4.017 +/- 0.007 billion years. This rock is probably a granitic intrusion which has since been deformed. But this intrusion must have been emplaced into rock which is still older, but as yet undated.