Plenaries

Each morning and afternoon, the science program starts with plenary lectures by eminent scientists. Confirmed speakers are listed below.

Monday 22nd June

Mark Harrison, Institute of Geophysics and Planetary Physics, UCLA
Probing the Dark Age: Crust-Water Interactions on Hadean Earth
Monday 22nd June, 08:30
The Hadean Eon (4.5-4.0 Ga) is the dark age of Earth history; there is no known rock record from this period. However, detrital zircons as old as ~4.4 Ga provide unprecedented insights into this formative phase of Earth history. Geochemical records from these ancient zircons are interpreted to reflect an early hydrosphere and felsic crust, "wet" granite melting in a low heat-flow environment, and even plate boundary interactions - in contrast with the traditional view of an uninhabitable, hellish world. Scenarios are explored with a view to reconciling this record with our knowledge of conditions then extant in the inner solar system.

François Morel, Department of Geosciences, Princeton University
Urey Medal Lecture: The Geobiology of Cadmium: From ocean to molecule
Monday 22nd June, 13:30

Tuesday 23rd June

Ken Farley, Division of Geological and Planetary Sciences, California Institute of Technology
Gast Lecture: Major events in the recent history of the solar system recorded by ³He in deep-sea sediments
Tuesday 23rd June, 08:30
Cosmic dust is extraordinarily enriched in 3He compared to terrestrial sediments, making it a sensitive tracer of the flux of fine-grained extraterrestrial matter to earth. Analyses of marine sediments demonstrate that this helium is preserved for at least several hundred million years, though it remains unclear what phase(s) are responsible for this preservation. Using 3He concentrations in sedimentary rocks my many collaborators and I have produced and attempted to interpret a record of the cosmic dust flux spanning the last ~100 Myr. The record reveals several multi-Myr episodes of enhanced flux, most prominently at 36 and 8 Myr. These episodes document the occurrence of important events in the history of the solar system. The timing and temporal evolution of the 8 Myr event are consistent with the collisional destruction of a 140 km diameter asteroid to produce the Veritas asteroid family. The enhanced ³He flux is maintained for ~1.5 Myr by a collisional cascade among resulting fragments. In contrast there is no known collision corresponding to the 36 Myr peak. The temporal evolution of the enhanced dust flux and the occurrence of several major terrestrial impacts at the peak of the event are more consistent with a comet shower produced by a close stellar encounter. However, other workers have presented geochemical evidence from the impacts themselves that may argue against such an origin. One postulated alternative is the occurrence of an asteroid shower, with dust derived from lunar impacts. We are continuing to push deeper into the past searching for additional events, and hope to reach at least 150 Myr of continuous record.

Mark Thiemens, Division of Physical Sciences, UCSD
Goldschmidt Medal Lecture: Mass Independent Isotopic Fractionations: Discovery and Recent Applications in Nature: Earth and the Early Solar System
Tuesday 23rd June, 13:30
A motivation for the the experiments of Thiemens and Heidenreich was to test the basic assumption that the only mechanism by which meteoritic mass independent isotopic compositions could be produced was via a nuclear process. That work has led to new theories and experiments in basic chemical physics and was the first to suggest that meteoritic oxygen and nitrogen isotopic compositions were the result of photochemical isotopic self shielding, now recently rediscovered. As in the case of the nuclear model, self shielding has several, crucial assumptions. 1) in the nebular dissociation process, the only fractionation derives from the optical filtration of photons by carbon monoxide. 2) Once the filtered light is absorbed, it leads to an immediate dissociation (quantum yield of one). These crucial assumptions have now experimentally been shown to be wrong (3). The experimental test was formidable because: 1) the only short UV source of sufficient photon fluence is synchrotron radiation and 2) at relevant wavelengths all windows are opaque and experiments must be done in a window free mode. In (3), these obstacles were overcome and self shielding was probed directly. The crucial parameters; shielding depth, wavelength (specific quantum states), and temperature were tested. The beam profile of the radiation is also directly measured to quantify the states. It is directly shown that 1) the quantum yield is far different from unity, 2) there is a thousands of per mil fractionation associated with the process of dissociation itself, which has nothing to do with self shielding as it also occurs at wavelengths where shielding is not possible. Further, the fractionation pattern does not produce the equal ¹⁷O,¹⁸O composition required for shielding and therefore there is no experimental support for self shielding models. The mass independent fractionation process has also been observed to occur in nature; in the Earth's atmosphere (Precambrian to present), Mars, and tests a multitude of geochemical processes which will be discussed.

Wednesday 24th June

Marty Goldhaber, US Geological Survey
Geochemical Society Presidential Lecture: The Impact of Humans on the Geochemical Landscape
Wednesday 24th June, 08:30
Vladimir Vernadsky, a pioneer of geochemistry, recognized as long ago as 1945 that “Man under our eyes, is becoming a mighty and ever-growing geological force”. Earth scientists are now documenting the accelerating influence of humans on the planet. A striking example is that continental sediment transport driven by agriculture and urbanization now dominates natural processes by an order of magnitude. Soil erosion in the continental US has been profoundly affected by cultivation over a relatively short period of settlement. Erosion yields in many areas are now exceeding 20 Mg/ha/y. We are only just beginning to appreciate the global implications of the loss of undisturbed soils and ecosystems on element cycling and biological sustainability. Earth surface processes are in part reflected in what A.I. Perel’man called the geochemical landscape–a term that embodies the interactions of the lithosphere with the hydrosphere, atmosphere and biosphere. The mining and burning of coal provides a conspicuous example of the extensive geochemical landscape modification by humans. The Appalachian coal basin spans nearly the entire eastern US and its coal is locally quite rich in Hg and As. Continental scale geochemical data sets show that As in both stream sediment and soil throughout the coal producing region is 5- 10 times higher than in adjacent areas. Atmospheric deposition of Hg originating from coal combustion, has resulted in advisories against fish consumption in over 30% of US lakes. Atmospheric Hg transport is now recognized as a global issue. The Central Valley of California is another region characterized by extensive modification during human habitation. Originally an inland sea, the northern valley is now totally transformed by dikes and levees to sustain agriculture and urbanization. An extensive geochemical survey of the valley shows that both Hg and placer Au mining on the east and west sides of the valley and massive sulfide mining to the north have significantly altered the geochemical landscape. of valley soil. These geochemical impacts can be traced down the Sacramento River and into the San Francisco Bay. As a famous naturalist, Aldo Leopold said, “The reaction of land to occupancy determines the nature and duration of civilization”. We need to heed his admonition.

The plenaries on Wednesday afternoon form part of the Earth's future event.

Thursday 25th June

Susan Stipp, Nano-Science Center, Department of Chemistry, University of Copenhagen, Denmark
NanoGeoScience: Cleaner water, more oil and taking out the garbage
Thursday 25th June, 08:30
The electronic age has been driven by developments in technology. The same instruments that have built the foundation for nano-technology have also launched a revolution in science, because for the first time in human development, we can see at the fundamental chemical level. We can see atoms and how they are arranged in a solid, and we can identify molecules and watch them react. This has enormous potential for gaining insight into why things happen and how. We can observe nature at a whole new level, learn its secrets, and use our new knowledge to find solutions to society’s challenges. Some examples include ensuring cleaner water, safer ways to store waste, discovering the mysteries of biomineralisation, getting more oil from reservoirs and immobilizing CO₂ in rock form, where it will be stable for geologic time.

Charles Prewitt Charles T. Prewitt, University of Arizona
History and Significance of ABX₃ Crystal Chemistry Investigations
Thursday 25th June, 13:30
There is substantial interest among the mineralogical and related communities in phase transitions involving materials with the general formula, ABX₃, e.g., MgSiO₃, CaSiO₃, FeTiO₃, FeGeO₃, NaMgF₃, Al₂O₃, Fe₂O₃, Gd₂S₃, and many others. The interactions of elements in these specific configurations provide an interesting framework for analysis of many different, but related properties. Although some of these phases are not considered to be major constituents of Earth's mantle, knowing their crystal-chemical behavior is considered to be essential for understanding overall mineralogical character and, in particular, how they react to changing environmental conditions. Recent developments based on synchrotron-related experiments provide powerful new tools, especially those that give new information on high-pressure, high-temperature mineral properties.

Friday 26th June

Susan Trumbore, UC Irvine and Max Planck Institute for Biogeochemistry (Jena, Germany)
Predicting the future: biogeochemical feedbacks between terrestrial ecosystems and climate
Friday 26th June, 08:30
The coming century will see changes in atmospheric composition and climate that exceed the envelope of those experienced by terrestrial ecosystems over the past million years. At the same time, increased human population will continue to expand and intensify land management. Predicting the consequences of these changes is a major challenge of our understanding of biogeochemistry. This talk will illustrate those challenges by exploring the processes that may dominate terrestrial feedbacks to climate change on decadal to century timescales, and suggest how we can detect whether those feedbacks are operating.