Source: University of Wisconsin-Madison
Illustration by: Dan Brennan.
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Caption: Microscopic view of a zircon crystal determined to be 4.4 billion years old making it the world's oldest known terrestrial material. Zircon is a mineral commonly used to determine the geological age of rocks. Chemical analysis of this grain suggests that the Earth was cool enough to have water, a hydrospehere and, possibly, life much earlier than previously thought.
Photo credit: courtesy John W. Valley, UW-Madison professor of geology and geophysics
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Caption: John Valley, geology and geophysics.
Photo credit: Jeff Miller
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