New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 28

capabilities have also explored thermal, electromagnetic, and dynamic coupling of the
inner and outer core regimes, seeking constraints on the inner core growth mechanism
and outer core energy budget (see Figure 2.9). Coupling between the mantle and outer
core and gravitational interaction between the mantle and inner core have been
explored with improved geodynamic simulations constrained by orbital observations.
Paleomagnetic observations have documented Earth's early magnetic field behavior
back to at least 3 billion years ago (see Box 2.3), providing valuable constraints on
geodynamo variations linked to inner core growth (Tarduno et al., 2007). All of these
approaches to quantifying core structure and history are building an observational
database on which major synthesis of core evolution should be viable over the next
decade.
The committee also anticipates major developments in understanding of
Earth's core through static high-pressure experiments and density functional theory
calculations. With newly developing high P-T techniques allowing direct access to
core conditions, novel experimental probes especially well suited for Fe and its
alloys, and advances in theoretical techniques for treating transition metals, the time
is ripe for a renaissance in studies that will provide improved understanding of the
thermal evolution, seismic structure, growth mechanism, magnetic field generation,
and dynamic behavior of the core.
Figure 2.9 Fluxes of heat and light elements (Si, C, O, S, etc.) from the mostly solid inner
core into the molten outer core provide much of the power for the geodynamo and also
influence the rate of inner core growth and the thermo-chemical evolution of the core as a
whole. New interpretations of these fluxes center on the significance of the seismic F-layer
above the inner-core boundary (ICB), which appears to be depleted in light elements
compared to the overlying outer core, and the observed dichotomy between eastern and
western hemispheres of the inner core This diagram shows one interpretation, the so-called
inner core translation instability, in which the inner core dynamics resemble that of a
continental glacier. Freezing on the western side of the ICB releases light elements in
buoyant plumes into the outer core, while melting on the eastern side of the ICB releases
iron-rich liquid, forming the dense F-layer. SOURCE: Reprinted from Alboussiere et al.
(2010) with permission from from Macmillan Publishers Ltd., and from Monnereau et al.
(2010) with permission from AAAS.