Encyclopedia of the Solar System 2nd ed

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CHAPTER 10

Earth as a Planet:

Surface and Interior

David C. Pieri

Jet Propulsion Laboratory

California Institute of Technology

Pasadena, California

Adam M. Dziewonski

Harvard University

Cambridge, Massachusetts

1. Introduction: the Earth as a Guide to Other Planets 6. Earth’s Radial Structure


2. Physiographic Provinces of Earth 7. Earth in Three Dimensions


3. Earth Surface Processes 8. Earth as a Rosetta Stone


4. Tools for Studying Earth’s Deep Interior Bibliography


5. Seismic Sources

1. Introduction: the Earth as a Guide to

Other Planets

The surface of the Earth is perhaps the most geochemically
diverse and dynamic among the planetary surfaces of our
solar system. Uniquely, it is the only one with liquid water
oceans under a stable atmosphere, and—as far as we now
know—it is the only surface in our solar system that has
given rise to life. The Earth’s surface is a dynamic union of
its solid crust, its atmosphere, its hydrosphere, and its bio-
sphere, all having acted in concert to produce a constantly
renewing and changing symphony of form (Figure 1).
The unifying theme of the Earth’s surficial system is
water—in liquid, vapor, and solid phases—which transfers
and dissipates solar, mechanical, chemical, and biological
energy throughout global land and submarine landscapes.
The surface is a window to the interior processes of the
Earth, as well as the putty that atmospheric processes con-
tinually shape. It is also the Earth’s interface with extrater-
restrial processes and, as such, has regularly borne the scars
of impacts by meteors, comets, and asteroids, and will con-
tinue to do so.
Our solar system has a variety of terrestrial planets and
satellites in various hydrologic states with radically differing
hydrologic histories. Some appear totally desiccated, such
as the Moon, Mercury, and Venus. In some places where

water is very abundant now at the surface, such as on the

Earth, and the Jovian Galilean satellite Europa (solid at

the surface and possibly liquid underneath), the Saturnian

satellite Enceladus (possibly erupting water vapor into

space through an icy surface), and Titan, Saturn’s largest

moon (where a 94◦K surface temperature makes water ice

at least as hard as granite). In other places, such as Mars and

Ganymede, it appears that water may have been very abun-

dant in liquid form on the surface in the distant past. Also, in

the case of Mars, water may yet be abundant in solid and/or

liquid form in the subsurface today. Thus, for understand-

ing geological (and, where applicable, biological) processes

and environmental histories of terrestrial planets and

satellites within our solar system, it is crucial to explore the

geomorphology of surface and submarine landforms and

the nature and history of the land–water interface where it

existed. Such an approach and “lessons learned” from this

solar system will also be key in future reconnaissance of

extrasolar planets. [SeeMars:Surface andInterior.]

2. Physiographic Provinces of Earth

2.1 Basic Divisions

From a geographic and geomorphologic point of view, es-

pecially when seen from space, the surface of the Earth

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