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A tiny speck of zircon crystal that is barely visible to the eye is believed to be the oldest known piece of Earth at about 4.4 billion years old. For the first time ever, the public will have a chance to see the particle Saturday at the University of Wisconsin-Madison, where researchers in 2001 made the breakthrough discovery that the early Earth was much cooler than previously believed based on analysis of the crystal.
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Analysis of the object in 2001 by John Valley, a UW-Madison professor of geology and geophysics, startled researchers around the world by concluding that the early Earth, instead of being a roiling ocean of magma, was cool enough to have oceans and continents — key conditions for life.

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Valley worked with William H. Peck, a former UW-Madison graduate student and now an assistant professor of geology at Colgate University, to analyze oxygen isotope ratios, measure rare earth elements, and determine element composition in a grain of zircon that measured little more than the diameter of two human hairs.
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"What the oxygen isotopes and rare earth analysis show us is a high oxygen isotope ratio that is not common in other such minerals from the first half of the Earth's history," Peck says. In other words, the chemistry of the mineral and the rock in which it developed could only have formed from material in a low-temperature environment at Earth's surface.