The oldest oceanic basalt crust today is only about 200 million years. Most of the continental crust is much older. The oldest continental crustal rocks on Earth are cratons between 3.7 and 4.28 billion years old. These have been found in the Narryer Gneiss Terrane in Western Australia, in the Acasta Gneiss in the Northwest Territories on the Canadian Shield, and on the Fennoscandian Shield. A few zircons at least 4.3 billion years old have been found in the Narryer Gneiss Terrane in Western Australia.