Geoscience Reference
In-Depth Information
plishment of the past decades has been to identify many of the key materials and
properties controlling the Earth's geological processes. A major intellectual
challenge that remains is to understand how material properties and processes can
be scaled from laboratory to planetary scales of distance and time.
THE CONTINENTS
Almost the entire span of Earth history is recorded in the continental crust.
Rocks on the surface of the continents provide an archive reaching back at least 4
billion years, 20 times beyond the oldest oceanic crust and almost nine-tenths the
age of the solar system. Thus the continents provide the only accessible long-term
record of the Earth.
The continents have grown by magmatism, deposition of sediments, and
crustal accretion and have been reshaped through tectonism, metamorphism, and
fluid flux from the deep Earth. Properly interpreted, continental geology yields
information about these processes and about the large-scale dynamics that
control mantle convection, planetary differentiation, plate motions, and climate
throughout Earth history. Today, many fundamental and controversial ideas
about the continents await testing through the integration of field geology and
geomorphology with new technologies in geochemistry, geophysics, and
geodesy.
In recognition of the need for broadly based, multidisciplinary studies of the
continents, EAR established the Continental Dynamics (CD) Program in 1982
with the objective of augmenting its highly successful core programs in tectonics,
geophysics, and geochemistry ( Appendix A ). The CD program has flourished,
sponsoring many regional investigations of the continental crust and upper mantle
around the globe, encouraging the development of new tools and setting the stage
for a new phase of investigation.
Recent Advances
Many of the most significant advances of the past decade have involved
integration of new remote-sensing data and computational technologies with field
and laboratory observations.
• The advent of geodetic techniques based on the Global Positioning System
(GPS) and interferometric synthetic aperture radar (InSAR) satellites has
made it possible to observe the motions of crustal fragments on time
scales from seconds to decades and to record relative positions accurate to
a
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