Press Images John W. Valley will speak at the University of Utah's March 8 Frontiers of Science Lecture about hell-like conditions during Earth's early history, and whether the planet cooled down earlier than once thought. To download high-resolution click here: Credit: Mary Diman, University of Wisconsin-Madison

When did hellish conditions subside on the early Earth so that oceans of molten rock could give way to solid land, oceans of water and early life? That is the subject of the University of Utah College of Science's March 8 Frontiers of Science Lecture by John W. Valley of the University of Wisconsin-Madison. To download high-resolution click here: Credit: Artwork copyright 2006 Don Dixon/cosmographica.com

Lecturer: John W. Valley, professor of geology and geophysics, University of Wisconsin-Madison
Date: Wednesday, March 8, 2006
Time: 7:30 p.m.
Place: Aline Wilmot Skaggs Biology Building Auditorium, University of Utah

FREE AND OPEN TO THE PUBLIC

When the Earth was formed some 4.5 billion years ago, it was an inferno of boiling metals, minerals and gases. Red-hot oceans of molten rock, massive meteorite strikes and even brimstone in the atmosphere justify calling this time period the Hadean, after Hades or hell.

These extreme conditions had to subside before continents could form, before vapor in the dense atmosphere could pool as liquid water and before the first primitive life could survive and evolve. But when was the end of the hellish Hadean period? Evidence from rocks has placed the boundary between the Hadean and the subsequent Archean Eon at about 3.8 billion years ago – the date of the oldest hints of life and sedimentary rocks that formed at low temperatures. The earliest known fossils are 3.5 billion years old.

However, the discovery of crystals of the mineral zircon – as much as 4.4 billion years old – from isolated locations in northwestern Australia has provided evidence that the Hadean ended much earlier than previously thought – perhaps 4.2 billion years ago or even earlier. The unusually durable zircon crystals have preserved ample evidence – in the form of mineral inclusions, trace elements and isotopes of uranium, lead, oxygen and hafnium – that oceans and land masses habitable to life existed when the crystals were formed. The study of these tiny “time capsules” is driving new technology, and yielding a wealth of knowledge about the Earth’s beginnings.

“While extreme opinions exist on both sides, a moderate suggestion is that small continental land masses existed by 4.4 billion years ago, that oceans hospitable to life existed by 4.2 billion years ago and thus the Hadean ended before 4.2 billion years ago,” says Valley. This concept of a cool early Earth represents a major departure from traditional ideas of how the Earth evolved.

Valley earned M.S. and Ph.D. degrees in geophysics at the University of Michigan, Ann Arbor in 1977 and 1980, respectively. He spent three years at Rice University in Houston as an assistant professor before accepting a faculty position at the University of Wisconsin-Madison in 1983. He was promoted to a full professor in 1989, and is currently the Charles R. Van Hise Professor of Geology and Geophysics at UW-Madison. Professor Valley was elected a Fellow of the Geological Society of America in 1992, and a Fellow of the Mineralogical Society of America in 1993. He is now the President of the Mineralogical Society of America. He has served as associate editor of the Journal of Geophysical Research, and associate editor of the American Journal of Science. In 2003, Valley received the N.L. Bowen Award, presented by the American Geophysical Union for his work on zircons from northwestern Australian rocks dating to the early Archean Eon.

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