100-C 25-C 50-C 75-C C+M 50-C+M C+Y 50-C+Y M+Y 50-M+Y 100-M 25-M 50-M 75-M 100-Y 25-Y 50-Y 75-Y 100-K 25-K 25-19-19 50-K50-40-40 75-K 75-64-64

CHAPTER 9

Earth as a Planet:

Atmosphere and Oceans

Timothy E. Dowling

University of Louisville

Louisville, Kentucky

Adam P. Showman

University of Arizona

Tucson, Arizona

1. Overview of Planetary Characteristics 5. Climate


2. Vertical Structure of the Atmosphere 6. Life in the Atmosphere–Ocean System


3. Atmospheric Circulation 7. Conclusions


4. Oceans Bibliography

E

arth is the only planet that orbits the Sun in the dis-
tance range within which water occurs in all three of
its phases at the surface (as solid ice caps, liquid oceans,
and atmospheric water vapor), which results in several un-
usual characteristics. Earth is unique in the solar system
in exhibiting a global ocean at the surface, which covers
almost three quarters of the planet’s area (such that the to-
tal amount of dry land is about equal to the surface area of
Mars). The ocean exerts a strong control over the planet’s cli-
mate by transporting heat from equator to pole, interacting
with the atmosphere chemically and mechanically, and, on
geological timescales, influencing the exchange ofvolatiles
between the planet’s atmosphere and interior. The Earth’s
atmosphere follows the general pattern of a troposphere at
the bottom, a stratosphere in the middle, and a thermo-
sphere at the top. There is the usual east–west organiza-
tion of winds, but with north–south and temporal fluctua-
tions that are larger than found in any other atmosphere.
Many of the atmospheric weather patterns (jet streams,
Hadley cells, vortices, thunderstorms) occur on other plan-
ets too, but their manifestation on Earth is distinct and
unique. The Earth’s climate has varied wildly over time,
with atmospheric CO 2 and surface temperature fluctuat-
ing in response to ocean chemistry, planetary orbital varia-
tions, feedbacks between the atmosphere and interior, and
a 30% increase in solar luminosity over the past 4.6 billion
years (Ga). Despite these variations, the Earth’s climate has

remained temperate, with at least partially liquid oceans,

over the entire recorded∼3.8 Ga geological record of

the planet. Life has had a major influence on the ocean–

atmosphere system, and as a result it is possible to discern

the presence of life from remote spacecraft data. Global bi-

ological activity is indicated by the presence of atmospheric

gases such as oxygen and methane that are in extreme ther-

modynamic disequilibrium, and by the widespread pres-

ence of a red-absorbing pigment (chlorophyll) that does

not match the spectral signatures of any known rocks or

minerals. The presence of intelligent life on Earth can be

discerned from stable radio-wavelength signals emanating

from the planet that do not match naturally occurring sig-

nals but do contain regular pulsed modulations that are the

signature of information exchange.

1. Overview of Planetary Characteristics

Atmospheres are found on the Sun, 8 planets, and 7 of the

60-odd satellites, for a total count of 16—in addition to

the atmospheres that exist around the∼200 known gas gi-

ant planets orbiting other stars. Each has its own brand

of weather and its own unique chemistry. They can be di-

vided into two major classes: the terrestrial-planet atmo-

spheres, which have solid surfaces or oceans as their lower

boundary condition, and the gas giant atmospheres, which

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