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Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth
E. B. Watson1* and
T. M. Harrison2,3
Ancient zircons from Western Australia's Jack Hills preservea record of conditions that prevailed on Earth not long afterits formation. Widely considered to have been a uniquely violentperiod geodynamically, the Hadean Eon [4.5 to 4.0 billion yearsago (Ga)] has recently been interpreted by some as far morebenign—possibly even characterized by oceans like thoseof the present day. Knowledge of the crystallization temperaturesof the Hadean zircons is key to this debate. A thermometer basedon titanium content revealed that these zircons cluster stronglyat 700°C, which is indistinguishable from temperatures ofgranitoid zircon growth today and strongly suggests a regulatedmechanism producing zircon-bearing rocks during the Hadean.The temperatures substantiate the existence of wet, minimum-meltingconditions within 200 million years of solar system formation.They further suggest that Earth had settled into a pattern ofcrust formation, erosion, and sediment recycling as early as4.35 Ga.
1 Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. 2 Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia. 3 Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA.
* To whom correspondence should be addressed. E-mail: watsoe{at}rpi.edu
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|Abstract »|Full Text »|PDF »
700°C, which is indistinguishable from temperatures of granitoid zircon growth today and strongly suggests a regulated mechanism producing zircon-bearing rocks during the Hadean. The temperatures substantiate the existence of wet, minimum-melting conditions within 200 million years of solar system formation. They further suggest that Earth had settled into a pattern of crust formation, erosion, and sediment recycling as early as 4.35 Ga. 
