研究概要

William F McDonough uses chemistry and physics to study the Earth and terrestrial planets in order to understand their formation, composition and evolution. Each of these four inner planets have a metallic core surrounded by a thick silicate sphere, both of which are enveloped by a dynamic biosphere, atmosphere and hydrosphere system, with the volumes of surface water/ice and air depending on the planet’s surface temperature. Curiously, as we continue to measure and understand these planets, we find that the initial amounts of metal, silicate and volatiles (gas, water and ices) differed, and that these differences likely reflect the distinctive building materials delivered to each planet’s formation zone that outwardly surround the Sun. The gatekeepers on this delivery system appears to be the forces of gravity pulling material into the Sun versus those same, but weaker forces produced by Jupiter, which pulled matter outwards. In addition, electromagnetic forces likely controlled to some extent the distribution of iron and related magnetic materials, which in turn lead to an iron rich core for Mercury and a bulk planetary density gradient in the solar system from Mercury to the asteroid belt.

While the forces of physics determined the delivery of local building materials for each planet, the forces of chemistry shaped the distribution of elements in each planet. In the earliest days of planetary formation some four and half billion years ago, planets grew in a solar system wide disk of gas and dust, with the gas mostly made up of hydrogen and much lesser amounts of helium and compounds of carbon, nitrogen, and oxygen. As the growing planet accreted mass it attracted a surrounding atmosphere, varying from a sparse to dense atmosphere of hydrogen mostly, and lesser amounts of water vapor and carbon compounds (e.g., CO₂, CO, CH₃, CH₄). A hydrogenrich atmosphere leads to a reduced condition, whereas excess oxygen leads to a more oxidized planetary result. Earth and Mars provide such a perspective, with the former being more reduced and the latter more oxidizing, as revealed by the amount of iron in the mantle and cores of these two planets. Earth has about 8.0 weight % FeO and Mars has about 15 weight % FeO in their respective mantles, which, in turn, resulted in their metallic cores being 1/3 versus 1/5 of their masses, respectively.

The retention and evolution of the atmosphere and hydrosphere of a planet is the weakest part of our understanding of these terrestrial bodies. We can determine the current surface mass of oceans, fresh water, ice cover and atmosphere, but we are at a lost to determine the amount of water and other volatiles in the Earth’s interior, nor the amount of these volatiles at the surface in times past. Our planetary abundance estimates of these elements (H, C, N, O, S) have large uncertainties when compared to estimates for the rest of the elements. The interior of the Earth is estimated to have about an ocean’s amount of water in its interior, but some have argued that it could be as much as 10 ocean masses.

The atmospheres of the planets are dynamic and ever evolving. The atmosphere of Venus is 100 times thicker than that of Earth and is rich in CO₂ (96.5 weight %) with minor amounts of nitrogen (3.5%) and negligible amounts of argon (700 ppm, part per million) and water vapor (20 ppm). Compared to Earth, Venus has 82% of its mass, 90% of its surface area, but only about 1/3 of its atmospheric mass (when the atmosphere of Earth and the hydrosphere are combined). Although Mars has a diameter of about 1/2 that of Earth, its atmospheric volume is only 1% that of Earth. In addition, the present atmosphere of Mars is a thousand times thinner than the current atmosphere of Earth, and the compositional contrast is strong. Earth has a nitrogen-rich atmosphere (78% by weight) with lesser amounts of oxygen (21%) and argon (1%), while Mars has 96% CO₂, 1.9% N2 and 1.9% Ar. The atmospheres on both planets were very different in the past, and multiple lines of evidence show that they evolved along different paths. Mercury’s atmosphere is transitory, its mostly due to surface heating and volatilization of alkali metals and other low-temperature metals as Mercury experiences diurnal surface heating cycles. Finally, the Earth is the only planet identified to contain a biosphere.

Our efforts in AIMEC focus on understanding the nature (that is, composition and structure), dynamics, and evolution of the marine ecological environment, particularly under human-induced changing conditions. Understanding the origins, variability, and rate of change of this environment on a range of spatial and temporal scales aids in giving context to dynamics, including connectivity, stability, and adaptability of the system and its parts.

研究分野

Understanding the composition, structure, and evolution of the Earth and other terrestrial planets is one of the dominant themes of my research. The differentiation of the Earth has created three separate and distinct reservoirs (i.e., the core, the mantle-crust system, and the biosphere-atmospherehydrosphere system). My expertise also includes the development and application of analytical instrumentation and neutrino geoscience. Using laser ablation systems and plasma mass spectrometers for the chemical and isotopic analyses of samples. I work with geologists, biologists, chemists, physicists, forensic scientists, and members of the US intelligence community. I am developing and improving methods for modeling and detecting the Earth’s geoneutrino flux (electron antineutrino) and antineutrino detection for nuclear monitoring.

略歴

William (Bill) McDonough was born and raised in Boston, Massachusetts, USA. He got his undergraduate degree in Anthropology at the University of Massachusetts/Boston. Later, after a short but lucrative career as consultant geologist, he got his master’s degree in geochemistry at Sul Ross State University in Alpine, Texas, spent 18 months at the Lunar and Planetary Institute and NASA/Houston before departing for his Ph.D. at Australian National University (ANU). He received his Ph.D. in geochemistry in 1988 and from September 1987 to September 1989 he was an Alexander von Humboldt fellow at the Max Plank Institute in Mainz, Germany. In late 1989 he returned to the ANU as a Research Fellow in Ted Ringwood’s group and left in 1994 for a Research Associate position at Harvard University. In 1995 he finally got the courage to publish chapter 5 of his Ph.D. dissertation, which was a study on the composition of the Earth. In 2000 he took up an associate professorship at the University of Maryland, later in 2005 becoming a professor. In 2017 he began sharing his time between the University of Maryland and Tohoku University, where he had a special professorship in Earth Sciences and the Research Center for Neutrino Science. In 2024 he joined the newly established AIMEC team and became an emeritus professor at the University of Maryland.

Bill has co-edited 2 books and edited another. He has published more than 200 peer reviewed articles in journals and books, $10.8M in research funding, and mentored 10 undergrad senior thesis (4 female), 8 MS thesis students (6 female), and 14 PhD students (4 female), with 4 students (2 MS / PhD) being racial minorities. His awards and recognitions include: President (2017-19), VGP-section (∼9000 members and affiliates) of the American Geophysical Union; Robert Wilhelm Bunsen Medal (2012), European Geosciences Union; Distinguished Alumni, Sul Ross State University (2011); Fellow, American Geophysical Union (2011); Fellow, Geochemical Society and the European Association for Geochemistry (2010); Copernicus Visiting Scientist, University of Ferrara, Italy (2010); Distinguished Faculty Award, CMPS, Board of Visitors, University of Maryland (2009); Fellow, Mineralogical Society of America (2009); Fellow, Geological Society of America (2003); Fellow, Alexander von Humboldt (1987).