Zircon gathered from Australia’s Jack Hills region is confirming scientists’ view of how the Earth cooled and became habitable 4.4 billion years ago. Researchers found that the rock is the oldest known material of any kind to have formed on our planet. Using atom-probe tomography and ion mass spectrometry, the team from the University of Wisconsin-Madison concluded from the rock sample that the Earth had a hydrosphere before 4.3 billion years ago. They also found that the planet was indeed a “cool early Earth” with temperatures low enough for liquid water, oceans, and a hydrosphere not long after the planet’s crust congealed from a sea of magma.
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