This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.

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Composition of the Continental Crust

Changes in Atmospheric Constituents and in Radiative Forcing

This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

A global plate motion model, named NUVEL-1, which describes current plate motions between 12 rigid plates is described, with special attention given to the method, data, and assumptions used Tectonic implications of the patterns that emerged from the results are discussed It is shown that wide plate boundary zones can form not only within the continental lithosphere but also within the oceanic lithosphere; eg, between the Indian and Australian plates and between the North American and South American plates Results of the model also suggest small but significant diffuse deformation of the oceanic lithosphere, which may be confined to small awkwardly shaped salients of major plates

Current plate motions

Mars has a north–south divide in the age of its surface, as judged by the density of impact craters. Altimetry data, which by inference provide a subsurface view of the planet, reveal that the divide is only skin deep.

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An older face for Mars.

In this thesis observations of Mercury’s rotational state were carried out, using orbital data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. First, a reference rotation model of Mercury was derived. New Solar System ephemerides were used to obtain updated values for the mean orbital period and plane of Mercury as well as the instantaneous Laplace plane. With the help of the obtained values the resonant rotation model was constructed and used for interpretation of actual observations of the rotational state of the planet. For the measurement of the rotational parameters of Mercury a novel approach consisting of a combination of digital terrain models from stereo images and laser altimeter data from MESSENGER was elaborated. The method was extensively tested using simulated data and the uncertainty of the parameter estimation was assessed. By applying this method to three years of MESSENGER orbital observations the rotational parameters, including the libration amplitude, the orientation of the rotation axis, and the mean rotation rate of Mercury, were measured. The libration amplitude was found to be 38.9± 1.3 arc seconds or 460 m at the equator. The obliquity of the rotation axis was observed to be 2.029 ± 0.085 arc minutes, which is very close to the orbital plane normal. The rotation period was measured as 58.6460768 days with an accuracy on the level of one second. This is lower than the resonant rotation value by 9.2 seconds, which is interpreted as the expression of a long-term librational motion. The measured rotational parameters define Mercury’s body-fixed frame and are critical for the coordinate system of the planet as well as the planning of future spacecraft missions. Additionally, the new rotational parameters combined with the gravity field information allow to draw conclusions about Mercury’s interior structure. The existence of Mercury’s large molten outer core could be confirmed and further constraints on the depth of the core-mantle boundary as well as the densities of mantle and core were derived.

Sean C. Solomon

Papers

An older face for Mars.

Mercury’s rotational state from combined MESSENGER laser altimeter and image data

The curious case of Mercurys internal structure

Mercury's 2nd-Degree Shape and Geoid: Lunar Comparisons and Thermal Anomalies

Tectonic activity on Venus