Texas A&M University |
Summer 1999 - Vol. 7, No.
1 |
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Sojourner ®, Mars Rover ® and spacecraft design and images © copyright 1996-97, California Institute of Technology. All rights reserved. Further reproduction prohibited. |
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Extra! |
Mars is currently
being investigated by the Mars Global Surveyor satellite and
Mars Pathfinder, a scientific lander. Data from these instruments
indicate growing evidence of the existence of ancient martian
oceans. Also, the potential (and highly controversial) existence of fossil evidence of life in meteorites that are believed to have come from Mars has heightened scientific and public interest in the question of life and water on Mars. Biogeochemical oceanographers at Texas A&M are interested in answering the question: If there were oceans on Mars, what might their chemistry have been like, and how might it be related to their disappearance? |
Above: The origin of canyon Nanedi Vallis, about 2.5 kilometers wide, is enigmatic. Features such as canyon terraces and the small, 200 meter-wide channel near the top of the image suggest continual fluid flow and downcutting. Other features suggest formation by collapse. | |
If we look at Earth's two nearest
neighbor planets, Venus and Mars, as they currently exist, a
situation is observed reminiscent of Goldilocks and the three
bears. Venus is too hot for liquid water, Mars is too cold, and
Earth is just right for liquid water -- and 70 percent covered
with it. |
Take a closer look at Mars' valleys and channels. |
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In addition to the evidence for flowing water, considerable evidence supports the existence of large bodies of water in Mars' northern hemisphere. Although the best evidence is associated with modestly sized lakes that fill gigantic impact craters (Hellas and Argyre), some scientists estimate that much of the northern lowlands were covered with water at some point in time. These lowlands cover roughly 30 percent of Mars' surface, and if surface water were concentrated in them it could have reached a depth of 100 to 2,800 meters. A liquid ocean could most easily have created large-scale erosional escarpments (steep slopes or cliffs), and the widespread presence of weathered surface rocks and soil, plus salts, supports the presence of extensive surface waters over a fairly long time. Landforms resembling Earth's glacial features suggests that glaciers existed on Mars, requiring a hydrologic cycle on early Mars involving liquid water that evaporated, condensed, and precipitated. |
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Extra! |
On Earth, no rocks are known to
have survived prior to the Archean Eon (starting 3.8 billion
years ago), and only very limited information from this period
is currently available from Mars. However, it is still possible
to calculate approximate values for important aspects of seawater
chemistry during this time period, based on other sources of
information, experiments, and reasonable assumptions about processes
such as weathering reactions. * Possibly, the concentration of calcium in seawater did not reach levels like that of modern seawater until the late Precambrian (about 600 million years ago) and thus may have constrained the timing of the "Big Bang" of organic evolution, the emergence of the shelled invertebrates at the beginning of the Phanerozoic, 550 million years ago. |
The change in
atmospheric CO2 influenced the ocean chemistry View a diagram of the change in Earth's atmospheric carbon dioxide. |
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Extra! |
A similar evolution of the early
martian atmosphere would result in freezing conditions, and the
hydrologic cycle would largely cease. During the period of freezing,
the oceans would act as a source of carbon dioxide, rather than
a reservoir for its removal. This would further slow the rate
of climate change on Mars, extending the persistence of liquid
water on the surface and giving life a greater time period to
evolve. (Diagram)
In summary, the chemical environments
in the oceans and atmospheres of early Earth and Mars were similar,
but Mars was probably considerably cooler-which raises the possibility
that conditions for the formation of primitive life were more
favorable on Mars than on Earth. Chemical weathering and removal
of atmospheric carbon dioxide resulted in the oceans on both
planets becoming less acid, and the major cooling during the
planets' first 0.5 to 1 billion years, resulted in climate conditions
that may have been similar to conditions found on these planets
today. On Earth, life has flourished in the past four billion
years, but too much cooling has turned Mars into a "frozen"
planet. Dr. John W. Morse is a biogeochemical oceanographer at Texas A&M University. His e-mail address is morse@ocean.tamu.edu.
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View a diagram of the geochemical cycle on early Mars for carbon. |
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