Science Opportunities - Basic Research Opportunities in Earth Science - page 64

geomagnetic field on very short time scales—from a year to a few decades— lies
at the heart of understanding some of the most important processes governing its
origin and temporal evolution. This is surprising, because prior work had
suggested that the field evolves only on much longer periods (104 years), far
beyond the time scale of direct monitoring. Three examples are torsional
oscillations in the core, the angular momentum budget of the core, and magnetic
“jerks”—changes in accelerations of the field observed on the Earth's surface.
Although the desire to understand the dynamo at a fundamental level
continues to motivate studies of the geomagnetic field, there is a growing
recognition that changes in the Earth's main field have important implications for a
wide range of practical issues, including biological evolution, the production of
carbon isotopes in the upper atmosphere by cosmic rays (essential for carbon
dating), and the exchange of angular momentum between components of the
Earth system. Rotation of the planet provides a dynamic link between the climate
system at the surface (atmosphere and oceans) and the fluid-solid core at the
center.
Inner Core
The dense, crystalline inner core, which is about two-thirds the size of the
Moon, is known to play a major role in the core dynamo process. In particular,
the presence of the inner core decreases the rate of change of the magnetic field
and prevents the field from constantly reversing (switching north and south
poles). Some numerical simulations of the core dynamo and some observations
suggest that it may rotate at a rate faster than the rest of the planet. If so,
observations of this “superrotation” could possibly allow monitoring of the
dynamic “climate” of the overlying fluid core. The origin, growth, and
subsequent evolution of the inner core remain shrouded in mystery. However, the
strong heterogeneity and anisotropy in seismic wave velocities discovered in the
past few years suggest that it is a technically active region with a rich geological
history.
Disciplinary Advances
The quality and quantity of data addressing deep-Earth structure and
dynamics are increasing at an extraordinary rate in several disciplines:
seismology, geomagnetic studies, geochemistry, and high-pressure studies of
Earth materials. As with most disciplines, important discoveries about the Earth
have invariably followed the development of new instruments, deployment of new
networks or application of new theoretical methods.