The oldest rock on earth
The oldest dated rocks on Earth are more than 4 billion years old, formed during the Hadean Eon of Earth’s geological history. Such rocks can be found in very few places, like the Canadian Shield, Australia, Africa and in a few other old regions around the world. The ages of these felsic rocks are generally between 2.5 and 3.8 billion 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 age (3.8 to 4.28 billion years ago) in the Nuvvuagittuq greenstone belt on the coast of Hudson Bay, in northern Quebec. Older than these rocks are crystals of the mineral zircon, which can survive the disaggregation of their parent rock and be found in younger rock formations. Three of the very oldest zircons have been found in Australia’s Jack Hills, They date back to almost 4.4 billion years ago. Trace elements in these zircons suggest they came from water-rich, granite-like rocks such as granodiorite or tonalite. That means Earth cooled quickly enough for surface water and continental-type rocks just 100 million years after the moon impact, the massive collision that formed the Earth-moon system.