The oldest dated rocks on Earth, as an aggregate of minerals that have not been subsequently melted or disaggregated by erosion, are from the Hadean Eon. Such rocks are exposed on the surface in very few places.
Some of the oldest surface rock can be found in the Canadian Shield, Australia, Africa and in other more specific places around the world. The ages of these felsic rocks are generally between 2.5 and 3.8 billion years. The approximate ages have a margin of error of millions of years. In 1999, the oldest known rock on Earth was dated to 4.031 ± 0.003 billion years, and is part of the Acasta Gneiss of the Slave craton in northwestern Canada. Researchers at McGill University found a rock with a very old model age for extraction from the mantle (3.8 to 4.28 billion years ago) in the Nuvvuagittuq greenstone belt on the coast of Hudson Bay, in northern Quebec; the true age of these samples is still under debate, and they may actually be closer to 3.8 billion years old. Older than these rocks are crystals of the mineral zircon, which can survive the disaggregation of their parent rock and be found and dated in younger rock formations.
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