The Geology Department is pleased to announce that the 33rd annual Woodford Eckis lectureship will be held on February 13th and 14th, 2013. This year’s honored guest, Dr. E. Bruce Watson, is the Institute Professor of Science at Rensselaer Polytechnic Institute, a geochemist and materials scientist whose experiments have helped shape our current understanding of conditions deep within the Earth.
Please join us!
At 8:15 PM in the Rose Hills Theater (Smith Campus Center), Dr. Watson will deliver a lecture entitled “The environment of earliest Earth: decoding the oldest zircons.” This talk is intended for a general audience, and is open to the public.
At 11AM in the Rose Hills Theater (Smith Campus Center), Dr. Watson will deliver a lecture entitled “Growth-rate effects on crystal composition: from phenocrysts to climate proxies.” This talk, while intended for a somewhat more technical audience, is also open to the public.
Full abstracts for both talks are provided below. For more information about Dr. Watson’s research and illustrious career, please visit his home page.
The environment of earliest Earth: decoding the oldest zircons
The time period in Earth history between 4.0 and 4.55 billion years ago is referred to as the Hadean Eon. Little is truly known about this interval of Earth history, but it is widely regarded as an energetic and defining period in our planet’s history. In recent decades, researchers have inferred that during this time period the Earth collided with a Mars-sized-object, formed a deep magma ocean, grew the first continents, suffered cataclysmic bombardment from space, and nurtured the emergence of life. However—given the limited geochemical record from this time—we must acknowledge that our perception of these events may be inaccurate and/or incomplete. The challenge is that we have essentially no rock record from this interval from which to gain direct insight into these processes (the oldest firmly dated terrestrial rock is “only” 4.06 billion years old).
Prof. Watson will provide a summary of the evidence gleaned over the past decade from 4+ billion-year-old zircons from Western Australia supporting the view that continental crust was already fully developed, plate tectonic-style recycling was well underway, and liquid water was present on Earth’s surface during the Hadean. The “zircon thermometer” developed at Rensselaer has led to the understanding that most Hadean zircons crystallized at temperatures consistent with those achieved during water-saturated melting of crustal rocks in processes not unlike those of more modern times. Zircon “oxygen barometry” suggests, further, that magmatic gases streaming into the Hadean atmosphere were much like today’s H2O-CO2-SO2-dominated volcanic emanations¾and unlike the methane-dominated, reduced assemblage hypothesized by earlier researchers. These findings may bear on the suitability of earliest Earth for complex organic molecules and life itself.
Growth-rate effects on crystal composition: from phenocrysts to climate proxies
The equilibrium compositions of minerals provide the principal means of gaining insight into the environment of mineral formation (T, P, fO2, pH, PCO2) and, indirectly, the conditions and dynamics of Earth systems. Applications cut across many disciplinary boundaries in the geosciences, including high- and low-T geochemistry, petrology, tectonics, paleoceanography and paleoclimate studies. In some instances, however, there is reason to be cautious in our assumptions about equilibrium. Rapid crystal growth can result in significant deviations from equilibrium between a crystal and its growth medium with respect to trace elements and isotope ratios. There are multiple potential causes of this “failed equilibrium” that do not require growth that is rapid in an absolute sense. Broadly speaking, the causes of non-equilibrium growth are traceable to dynamical phenomena occurring at or near the interface between the growing crystal and its surroundings. Prof. Watson will discuss these causes in the context of experimental measurements and theoretical considerations, emphasizing the need for fundamental understanding, as well as the optimistic view that minerals will continue to serve us well in illuminating natural processes.