330 Encyclopedia of the Solar System
material though the mantle, and climatic conditions that
hindered the flow of water across the surface have limited
erosion and deposition to almost negligible levels for most of
the planet’s history. Since the end of heavy bombardment
around 3.8 billion years ago, the rate of all geologic pro-
cesses has been orders of magnitude lower than on Earth,
so that even ancient geologic features are well preserved.
The result is a geologic record, preserved on the surface,
that spans almost the entire history of the planet. For the
heavy bombardment period, we have compelling chemical
and mineralogic evidence for aqueous alteration and bodies
of water at the surface. Similar evidence for later periods is
sparse, although geomorphic evidence indicates that there
were episodic large floods. The climatic implications of the
geologic observations remain uncertain. Even though early
Mars must have had at least warm climatic episodes, any
warm episodes after the end of heavy bombardment must
have been very short because the cumulative amounts of
erosion and weathering are so small. What caused the early
warm conditions remains a mystery.Bibliography
Baker, V. R. (1982). “The Channels of Mars.” Univ. Texas Press,
Austin.
Beatty, J. K., and Chaikin, A. (1990). “The New Solar System.”
Sky Publishing, Cambridge, Massachusetts.
Carr, M. H. (1981). “The Surface of Mars.” Yale Univ. Press,
New Haven, Connecticut.
Carr, M. H. (1996). “Water on Mars.” Oxford Univ. Press, New
York.
Hamblin, W. K., and Christiansen, E. H. (1990). “Exploring
the Planets.” Macmillan, New York.Nature412,207–253 (2001).
A group of review articles on various aspects of the evolution of
Mars.
Wilford, J. N. (1990). “Mars Beckons.” Knopf, New York.