A Tale of Early Earth Told in Zircons

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Science  23 Dec 2005:
Vol. 310, Issue 5756, pp. 1914-1915
DOI: 10.1126/science.1121536

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The period just after the formation of planet Earth is an unknown time; no pristine rock or mineral specimens exist to provide data on composition. With the improvement of isotopic dating methods, the duration of this "dark age" has become shorter and shorter. In his Perspective, Amelin discusses results reported in the same issue by Harrison et al. in which zircon grains (zirconium silicate) were used to study the prehistory of Earth's oldest rocks. The technique relies on the radioactive decay of lutetium-176 to hafnium-176, which occurs with a half-life of 37 billion years. The data push back our knowledge of Earth's history to less than 100 million years after planetary accretion and provide important insights about how Earth formed and evolved.