A timeline shows the geological context of Jack Hills zircons, ancient minerals that formed when the Earth was less than 500 million years old. Chemical analysis of these tiny crystals by University of Wisconsin-Madison geologists Takayuki Ushikubo and John Valley suggests that rocky continents and liquid water existed on Earth at least 4.3 billion years ago. Evidence of heavy weathering by a harsh climate may help explain why no rock samples older than 4 billion years have ever been found. Image credit: courtesy Andree Valley Photo Date: June, 2008

Pictured is a false-color microscope image of a 4-billion-year-old zircon, a tiny mineral used to study the ancient rocks in which it formed. Chemical analysis of this crystal by University of Wisconsin-Madison geologists Takayuki Ushikubo and John Valley suggests that rocky continents and liquid water existed on Earth at least 4.3 billion years ago. Evidence of heavy weathering by a harsh climate may help explain why no rock samples older than 4 billion years have ever been found. Image credit: courtesy Mary Diman and John Valley (UW-Madison) Photo Date: June, 2008

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