Science Opportunities - Basic Research Opportunities in Earth Science - page 48

Recent scientific developments are illustrated in the following examples: 8
• Experimental discovery and initial characterization of the high-pressure
metallic state of hydrogen, considered to be the predominant material
making up the interiors of giant planets and stars—its existence was
theoretically predicted 60 years earlier, but the new measurements reveal
unexpected properties for metallic hydrogen and are leading to
significantly improved models of the structure, dynamics, and evolution
of giant planetary interiors. Understanding giant planets is required to
decipher the origin of planetary systems (including our own) and is
further motivated by the recent discovery of giant planets outside the solar
system.
• The friction laws for rock, including its dependence on sliding velocities,
have been determined experimentally for the first time, providing new
insights into the physics of earthquake rupturing and unifying many
observations of seismic phenomena that are relevant to assessing
earthquake hazards. Moreover, rock has been found to exhibit highly
nonlinear properties (e.g., in elastic wave propagation) among other
reasons, because of the chemical and physical interactions of fluids with
the formation and propagation of fractures at microscopic to tectonic
scales. Nonlinearity means that small forces can have large effects.
• Newly discovered mineral phases that are formed at high pressures lock
water, carbon dioxide, and other “volatile” molecules into their crystal
structures. The Earth's interior is thus likely to contain far more water and
other volatile species than the hydrosphere, fundamentally altering
current views of how the oceans and atmosphere have evolved over
geologic time.
• Novel techniques are revealing for the first time the physical structures
and chemical properties of mineral surfaces ( Figure 2.10 ). Experimental
measurements and theoretical analyses are providing a molecular-scale
understanding of the detailed interactions between fluid (within pores or
along grain boundaries) and mineral phases, with far-reaching
implications for disciplines ranging from volcanology to seismology and
for applications ranging from resource extraction to environmental
remediation. In particular, the details of fluid-mineral interactions
determine the degree, rate, and paths with which surface and underground
contaminants migrate and the means by which such effects can be
mitigated.
• Land resources are composed of soils with active colloidal fractions
dominated by organic-mineral nanophases whose surfaces control the
chemical speciation and fate, mobility, bioavailability, reactivity,
transport,
8 See also Microscopic to Macroscopic: Opportunities in Mineral and Rock Physics
and Chemistry, results of a workshop held in Scottsdale, Arizona, May 28-30, 1999.