Climate and Global Change Atmospheric and Environmental Chemistry Dynamics of the Atmosphere and Other Geophysial Fluids The Paleogeographic Atlas Project High Pressure Geophysics Geochemistry and Cosmochemistry Igneous and Metamorphic Petrology Paleontology and Evolution Other Departments and Related Institutions Affiliated Centers

Cosmochemistry is the study of the distribution of the elements and their isotopes in the cosmos. Different stars have different isotopic compositions, and a mineral grain that condenses in he cool envelope of a star inherits the isotopic composition of that star. The gaseous and granular debris of many stars accumulates in large interstellar clouds. The solar system formed when an interstellar cloud underwent gravitational collapse, forming a relatively dense and hot, disc-shaped cloud called the solar nebula in which most of the pre-solar grains were evaporated, the isotopic composition of the gas nearly completely homogenized by stirring, and condensation of solar system matter took place as the gas cooled. Some grains accumulated into planet-sized bodies which underwent volcanism and, in some cases, evolution of an atmosphere and weathering, processes which obliterated mineralogical, chemical and isotopic clues to the origin of the grains that accreted into such planets. Some grains accumulated into small, asteroid-sized bodies which effectively refrigerated the grains for all of solar system history, preserving mineralogical, chemical and isotopic features indicative of their origin as solar nebular condensates and, in some cases, even as pre-solar condensates which somehow also managed to escape the hot stage of the solar nebula. Chondritic meteorites which fall on Earth are samples from these small bodies.

Continuing a long tradition at the University of Chicago, the Department of the Geophysical Sciences has a particularly strong program in cosmochemistry, touching on all aspects of the origin of solar system matter.

Robert Clayton and Andrew Davis have developed Resonance Ionization Mass Spectrometry, an ultra-sensitive method for measurement of isotopic compositions of minor elements in tiny, individual interstellar grains extracted from chondrites. In order to study isotopic anomalies due to incomplete homogenization of pre-solar components in the nebular cloud, Robert Clayton uses mass spectrometry on materials separated from chondrites, while Andrew Davis, Steven Simon and Lawrence Grossman use the ion microprobe on individual grains in polished thin sections of chondrites. In order to understand how pre-solar SiC and graphite grains survived passage through the solar nebula, Ruslan Mendybaev and Lawrence Grossman measure the evaporation rates of these minerals in simulated gases of solar composition using gas-mixing apparatus. Denton Ebel and Lawrence Grossman use thermodynamic models to predict the sequence of condensation of minerals and liquids from cooling gases of cosmic composition. Steve Simon, Andrew Davis and Lawrence Grossman use the scanning electron microscope, electron microprobe and ion microprobe to study the textures and major and trace element contents of mineral grains in Ca-, Al-rich inclusions, thought to be the highest-temperature condensates from a gas of solar composition, in carbonaceous chondrites. Frank Richter and Andrew Davis use the ion microprobe to study crystal-liquid partitioning and isotopic fractionations produced when Ca-, Al-rich inclusion compositions are partially melted and evaporated in a simulated gas of solar composition.

Another source of extraterrestrial material is interplanetary dust particles, tiny grains of which constantly rain down on the Earth. Ian Steele uses the electron microprobe and cathodoluminescence to study the minor element content of olivine in these particles in an effort to ascertain their relationships to olivine in chondrites, and Stephen Sutton studies the trace element contents of these particles by Synchrotron X-ray Fluorescence.

Meenakshi Wadhwa uses mass spectrometry to elucidate the time-scales of early solar system events by combining isochron measurements for long-lived radionuclides and isotopic compositions of radiogenic daughters of short-lived, extinct nuclides in pre-solar grains, solar nebular materials in chondrites and very ancient igneous rocks in differentiated meteorites.

In these endeavours, members of the Department of the Geophysical Sciences enjoy close association and collaboration with James Truran in the Department of Astronomy and Astrophysics, who is an expert in stellar nucleosynthesis, and Roy Lewis in the Enrico Fermi Institute, a co-discoverer of interstellar grains in meteorites who continues to extract them and measure the isotopic compositions of their noble gases. Our ability to teach courses on meteorites and cosmochemistry and to perform analytical work on meteorites is greatly enhanced by our close research ties to the Field Museum of Natural History, repository of one of the world's great meteorite collections, only five miles from campus.

Specific research areas include:

• the chemical and isotopic constitution of the solid Earth, the Moon, and meteorites with implications for their origin and evolution: - isotopic studies of interstellar grains using CHARISMA; stable isotope analysis of C, N, O, Mg, Si, K, and ion microprobe analysis, of meteoritic and terrestrial materials; equilibrium stable isotope distribution and thermometry (Clayton)
• condensation of the earliest solids and liquids in the solar nebula; INAA, EMP and IMP analysis of the constituents of primitive carbonaceous chondrites, particularly CAIs, and their relation to processes in the solar nebula; laboratory studies of interstellar grain survival (Grossman)
• laboratory and theoretical studies of chemical processes controlling trace element and isotopic distribution in geochemical systems from molten CAIs and magmas to chemical sediments in deep-sea cores (Richter)

Relevant Faculty include:

• Alfred T. Anderson, Jr., Volcanology (Professor Emeritus)
• C. Kevin Boyce, Paleobotany
• Fred Ciesla, Meteoritics, Cosmochemistry, Joining the Department in July 2008
• Robert N. Clayton, Isotope Geochemistry (Professor Emeritus)
• Albert Colman, Biogeochemistry, Joining the Department in January 2008
• Nicolas Dauphas, Cosmochemistry
• Andrew Davis, Cosmochemistry
• Lawrence Grossman, Cosmochemistry
• Dion L. Heinz, High Pressure Geophysics
• Pamela Martin, Paleoceanography
• Frank M. Richter, Geochemistry
• David Rowley, Tectonics