Oldest known fragment of Earth's crust suggests early cooling

A tiny zircon crystal from Australia, 4.4 billions years old, has been confirmed as the oldest discovered fragment of Earth's crust, scientists say. A study of the crystal, led by University of Wisconsin-Madison geoscience Professor John Valley, shows the Earth's crust first formed just 160 million years after the formation of the solar system, the university reported Monday. The research gives new insight into how Earth cooled from a ball of magma and formed continents much earlier than previously believed, Valley said. "This confirms our view of how the Earth cooled and became habitable," said Valley, whose studies of zircons, the oldest known terrestrial materials, have helped portray how the planet's crust formed during the first geologic eon. "This may also help us understand how other habitable planets would form." It strengthens the theory of a "cool early Earth," he said, where temperatures were low enough for liquid water not long after the planet's crust congealed from a sea of molten rock. "The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago," and possibly life not long after, Valley said.