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VELIKOVSKIAN Vol. II, No. 2
CHZ and Solar System Stability
In 1984, C. Leroy Ellenberger raised the issue of the "Continuously Habitable Zone" (CHZ) as an argument against placing the Earth in an orbit closer to the Sun than that of Venus. 
To appreciate the precarious position of the Earth today, it should be borne in mind that, without the atmosphere, the average temperature would be well below the freezing point of water, just as it is on the Moon. If Earth actually was so close to the Sun as 0.7 AU [(Astronomical Units); 70% of its present distance or about 65 million miles instead of about 93 million miles] and climate was roughly comparable to now, then the Sun's output would necessarily have to have doubled since that time in order to maintain nearly constant conditions on Earth. Such a drastic change in a star like the Sun is unaccounted for by present theory. 
According to Ellenberger, there is a very narrow distance from the Sun at which the temperature "could be hospitable to life." 
Ellenberger explains that these calculations and analyses "reduced the Continuously Habitable Zone to a narrow range extending from 0.95 AU to 1.01 AU." This is a belt measuring from 88 to 94 million miles in which life can exist. Outside this narrow belt one must conclude that, given the present nature of the Earth, life could not survive in its present forms. If the Earth was less than 88 million miles from the Sun, the additional heat supplied at that closer distance would heat up the Earth to so as to kill all of Earth's life forms. On the other hand, if the Earth was more than 94 million miles from the Sun, the lack of sufficient heat from the Sun would make the Earth so cold that, again, it would kill the life forms on Earth.
What Ellenberger has not taken into account in his presentation is the definition of the CHZ. This was explored by Su-Shu Huang. 
Life, as understood on Earth, is essentially related to liquid water. Without liquid water, most life forms on Earth would not exist. In essence, the Continuously Habitable Zone is the
region in which a planet can retain a significant amount of liquid water at its surface, assuming a suitable atmospheric pressure. The climate extremes that would prevent a habitable Earth are, then, the cases where all the water has been evaporated from the surface (runaway greenhouse) or where Earth has become completely glaciated (ice catastrophe). 
If the Continuously Habitable Zone is truly a narrow belt a defined distance from the Sun, as Ellenberger has presented, then certain overwhelming problems emerge which suggest that the solar system could never have been stable. In particular, I will demonstrate that Venus, Earth and Mars could not have been in their present orbits since the formation of the solar system nor could they exhibit their historical and present characteristics because the nature of the Continuously Habitable Zone forbids this!
Ellenberger has stated that "[a] discouraging aspect of investigating Velikovsky's scenario is that solving one problem often entails either creating or confronting an even greater problem; thus, no final solution is achieved." 
What Ellenberger and other Velikovsky critics have not understood is that their criticisms of Velikovsky's theory have precisely the same obstacles that confront their own scientific theories. Their evidence often offers support for Velikovsky's hypothesis and contradicts their own assertions. When confronted, they resort to unscholarly behavior, such as name calling and ignoring the facts, as James E. Oberg has done. 
The Earth, Venus and Mars are supposed to have had abundant water on their surfaces sometime in the early history of the solar system, however, based on the scientific understanding of the Continuously Habitable Zone, this is fundamentally impossible. The point that Ellenberger missed and which Michael H. Hart explains is that our knowledge of the evolution of solar luminosity places the center of the habitable zone as moving outward from the Sun. Thus, the belt in which water could exist on a planet, specially the inner planets, is different for different planets at different periods. If Venus, Earth and Mars had always been in their present orbits, Venus would have had water on its surface while the surfaces of Earth and Mars would have been frozen. Both the Earth and Mars would have been in the midst of an Ice Age for billions of years before the belt of heat expanded outward from the Sun to encompass the Earth's orbit.
Ellenberger has ignored this problem. The nature of this early Sun paradox was described theoretically in 1975 by Roger K. Ulrich, who noted that the Sun, behaving like other main sequence stars of its mass, grows more luminous over time by 30 to 40% of its present state.  Therefore, the early Earth received from 30 to 40% less light than at present and would convert this lower luminosity to much less heat than at present. While Venus was covered by an ocean, the Earth's water was frozen solid.
James Pollack worked with the Venus greenhouse effect and analyzed the early solar luminosity. He suggested that "runaway greenhouse conditions were not reached on Venus until halfway through its history."  Given the solar system history of 4.6 billion years, Venus was outside the hot side of the Continuously Habitable Zone only 2.3 billion years ago. Thus, the Earth would have had an Ice Age well past that time because it would take longer for the Sun's luminosity to increase enough to move the CHZ from Venus' orbit to Earth's orbit.
In order to circumvent this problem, Carl Sagan and George Mullen have suggested that the Earth may have had sufficient ammonia gas in its atmosphere to generate a greenhouse effect.  But this suggestion faces the same problem Sagan and Mullen faced with respect to Venus. In its early history, the Earth did not have much oxygen in its atmosphere. According to Pollack:
Practically no ammonia should have been outgassed by volcanoes into the early atmospheres [of either Venus or Earth]. Moreover, NH, is easily broken down by ultraviolet radiation into nitrogen and hydrogen, and it is very difficult to recombine these two back into the parent molecule. Therefore, ammonia is probably not the agent involved in the early greenhouse enhancement. 
Ann Henderson-Sellers and A. J. Meadows suggested that the Earth's early atmosphere was opaque to escaping infrared light.  Tobias Owen, Robert D. Cess and V. Ramanathan suggested that the Earth's early atmosphere had a higher content of carbon dioxide to allow for water on its surface because of a greenhouse effect. 
There is a fundamental problem with the idea that carbon dioxide in the early Earth's atmosphere created a moderate greenhouse to allow for liquid water (oceans) on the Earth. If the atmosphere held sufficient CO2 to heat up the early Earth, then the greenhouse effect would increase as the Sun's luminosity increased over time and would produce a "runaway greenhouse" on the Earth! What the scientists are doing is playing a game of hide and seek with carbon dioxide. The carbon dioxide is available to generate a moderate greenhouse effect in the Earth's early atmosphere; however, as the Sun becomes more and more luminous, the CO2 behaves differently than it does on Venus: It begins to disappear, so the Earth does not generate a runaway greenhouse effect.
The idea of the runaway greenhouse effect on Earth is both illogical and contradictory. If the conditions on the early Earth were the same as on Venus, then the Earth would have had to develop a runaway greenhouse effect. To argue that for some unknown reason it did not occur is nothing but hand waving.
We must also consider the nature of the oceans. Carbon dioxide plays an important role in the chemistry of the oceans. As William W. Rubey stated in "Geologic History of Sea Water":
Carbon plays a significant part in the chemistry of sea water and in the realm of living matter. The amount now buried as carbonates and organic carbon in sedimentary rocks is about 600 times as great as that in today's atmosphere, hydrosphere and biosphere. If only 1/ 100 of this buried carbon were suddenly added to the present atmosphere and ocean, many species of marine organisms would probably be exterminated. Furthermore, unless CO2 is being added continuously to the atmosphere-ocean system from some source other than rock weathering, the present rate of its subtraction by sedimentation would, in only a few million years, cause brucite [Mg(OH)2] to take the place of calcite [CaCO2] as a common marine sediment.  (Emphasis added.)
The oceans are constantly removing CO2 from the atmosphere. Since the early Earth had oceans, CO2 did not accumulate in great amounts in the atmosphere. If we had had more CO2 into the atmosphere then, it would have acted as a greenhouse gas and would have heated up the oceans, which would have then released more CO2. Again, we go from a greenhouse effect to a runaway greenhouse effect. There is no escape from the Continuously Habitable Zone dilemma as outlined.
With Mars, the dilemma only deepens. Mars has supposedly been outside of the Continuously Habitable Zone since its birth 4.6 billion years ago, according to those who advocate a stable solar system. According to Everly Driscoll:
Mars has thrown a monkey-wrench into the way scientists study the history of the solar system.
Planetary scientists compare the atmospheres of Earth, Venus and Mars and extrapolate back to the original solar nebula to try to explain how each planet evolved. But they are finding it difficult to explain what Mars has been in the past by looking at what it is now.
The photographs taken by Mariner 9 were a shock....There are huge volcanoes, large faults and rift valleys and channels.
The channels are the biggest enigma. There are three types and at least two appear to be water-eroded tributaries and valleys. Some scientists [do not] believe it. Others, such as Paul Lowmay of the Goddard Space Flight Center, say the branch-like [or tributary] channels are "conclusive proof" of liquid water.
How to explain this evidence for liquid water on Mars has become one of the hottest issues in space science. It has stimulated all kinds of creative finagling and rethinking. 
All sorts of phenomena have been introduced to put liquid water on Mars' surface. Carl Sagan proposed that either the Sun may have been more variable or that Mars' axis may have been tilted much more than its present 24°.  These concepts were found to be unworkable, however.
If the Sun heats up more and generates more heat on Mars so as to allow liquid water to flow, it would also generate more heat on the Earth and kill all life on the planet.
In Sagan's criticism of Velikovsky, Sagan claimed that if Earth and Venus interacted, all life in the seas would be heated, perhaps, to extinction. Yet, he had no qualms in heating up Mars by causing the Sun's heat to rise and fall, and omitted from his discussion that, if his hypothesis was correct, this phenomenon would not only create a runaway greenhouse on Earth but would also destroy all life on the Earth.
Present-day scientists propose that in the early history of the solar system, Venus, Earth and Mars--at significantly different distances from the Sun with respect to the Continuously Habitable Zone--all had liquid water on their surfaces. Yet, Ellenberger ignores this contradiction to his views of solar system stability. Had he been paying attention to what was being said, he would never have raised this point. This problem does not need to be explained by the Velikovskians but by Ellenberger and the Establishment. If, as Ellenberger suggests, the Continuously Habitable Zone is so narrow that it precludes liquid water on planets outside this region, how does he explain water on Mars? Of course, one can invent a whole collection of gases for Mars, another collection of gases for the Earth and another collection for Venus to resolve this dilemma; or one can ignore the dilemma and privately attack this evidence with a "postcard meltdown" to avoid the painful problem inherent in this analysis.
If, as is proposed, there is a fairly narrow range of distances from the Sun at which liquid water will flow, then one must abandon solar system stability. Mars, at its present distance from the Sun, would require highly specialized atmospheric conditions in order to possess liquid water.
As Pollack pointed out: "Regardless of the sources, these worlds [Venus, Earth and Mars] obtained comparable initial endowments of volatiles, specially in the cases of Earth and Venus."  If the terrestrial planets received similar constituents which were outgassed after they formed, then all these planets would outgass similar constituents. Thus, one cannot have one set of gases for Venus and Earth, yet a totally different set of gases for Mars.
The concept that Mars and the Earth, in the early history of the solar system, could have had moderate greenhouses due to carbon dioxide abundance is without merit. It is presently thought that Martian ice caps contain abundant carbon dioxide. But, as each hemisphere of the planet goes through its summer-winter seasonal changes, these caps decrease in size in summer and increase in size in winter. The winter temperature is so low that CO2 condenses out of the atmosphere. In Mars' early history, its temperature would have been far lower than it is presently and any CO2 would have condensed out of its atmosphere, never allowing any kind of greenhouse to warm up the planet. The same is also true for water, which freezes at much higher temperatures than CO2. The same must also apply to the Earth, which had to have been at least as cold in its early history as Mars is now. This, in fact, is now understood and, according to James F. Kasting, an atmospheric scientist at the
National Aeronautics and Space Administration's (NASA's) Ames Research Center, all the early Mars calculations were too optimistic about greenhouse warming." 
The present model assumes that Venus, the Earth and Mars had additional internal heat in their early history. Since the Earth and Venus are much larger bodies than Mars, they would have remained warmer for a longer period of time. Thus, Venus' internal heat, added to its greenhouse gases, was capable of starting an early runaway greenhouse effect; Earth's early oceans stayed warm enough to allow for water until the CHZ moved outward to the Earth; and Mars, a small planet, lost its heat more rapidly and then lost its atmosphere and water, which escaped into space.
What the scientists have done is to shift their paradigm for the birth of planets as cold bodies to warm ones in order to make the planetary water history fit the evidence. But the paradigm still does not work. If Mars had lost its water 3 or 4 billion years ago, erosion would still have removed all evidence for river systems. The scientists categorically refuse to face up to the obvious fact that erosion on Mars would have turned the entire planet surface to sand, erasing all evidence of river systems. Therefore, this paradigm shift cannot be used to explain Mars' surface features. Now, if the paradigm shift fails to account for water on Mars, it cannot be used for the Earth and Venus. What is required, then, to save the warm planet theory is to have the much smaller terrestrial planet, Mars, keep its primordial heat an enormously long time so that it could maintain water on its surface for billions of years and river valley systems could still be seen. If Mars, a small planet, could stay warm for billions of years, then the Earth and Venus would have been warmer due to their size. Therefore, both would have to have runaway greenhouse effects. As the Sun heated up over time, the additional heat it provided to Venus and to the Earth would produce a runaway greenhouse effect on the Earth for an extended period of time. The Earth, like Venus, would have also lost its water. The Earth would never have kept its oceans under the conditions of the warm planet model. A runaway greenhouse on Earth would have melted the surface and caused all the continents to flow away. The new paradigm is as unworkable as are its predecessors. We are faced with a model that is wrong because its assumption of early warm planets still does not match with what is found on Mars and on the Earth. Again, I challenge critics to resolve this problem for Mars and the Earth and to resolve the problem of erosion on Mars.
Based on the clear evidence of erosion, Mars had to have had water on its surface within the last few thousand years. Wind erosion would have removed its river system topography long ago. This evidence is so clear-cut that no one has come forth to explain how Mars, given its present erosion rate, could still have clearly discernible river system topography on its surface.
Erosion on Mars, with respect to craters and river systems, is another dilemma.
Scientists tell us that, based on the crater counts on Mars' surface, we are looking at a surface that is 3 to 4 billion years old.  We have also been told that the river systems on Mars are 3 to 4 billion years old. However, any analysis based on uniformitarian erosional processes fails to correlate the ancient impacts with ancient river systems. The problem has to do with crater sizes and counts on the Martian surface. David Morrison and Tobias Owen touch upon this problem:
Mars has fewer large basins than the Moon, in spite of its much larger surface area. What does this mean? One possibility reflecting a uniformitarian outlook is that the many basins that formed early in Martian history have been degraded beyond recognition by subsequent geologic activity, perhaps including extensive erosion.  3 (Emphasis added.)
Morrison and Owen remove the giant, maria-like basins on Mars by erosion and other processes but never discuss how the ancient river systems will survive such massive erosion.
As I examine the scientific hypotheses presented, with regard to the observed evidence, I find that what they are proposing is simply impossible. Thomas A. Mutch and his colleagues analyzed the cratering count population on Mars, stating that
[i]f crater production and crater modification [erosion] have both proceeded at constant rates [based on uniformitarian theory] throughout Martian history, then the diameter-frequency curve for each morphologic type [size] should mimic the curve for all craters. Each curve will display a critical diameter below which equilibrium is attained. Equilibrium slopes [on charts] for all morphologic types will be identical to the slopes for all craters, although the frequencies [of the impacts] will be decreased. This illustrates the fact that each crater spends a fixed amount of time in a youthful, mature and old-age state. The situation is analogous to human populations. Although each person grows older, the number of persons of particular age is constant with time--assuming that birth rate and expected lifetime also remain constant.
Martian craters do not show the parallel relationship just described. Different morphologic types show frequency maxima at different diameters, and as such, deviate markedly from the distribution described by all craters. The curve can best be duplicated by a model in which there is a prominent high-intensity spike in the erosion history.
Therefore, in order to get rid of the largest basins from early Martian history and create a population of craters that deviates from the expected curve--comprised of many craters measuring a specific diameter and few craters measuring different diameters--an erosion catastrophe must be invoked.
Mutch and his colleagues continue:
It is easiest to imagine instantaneous blanketing [covering the craters with detritus or eroding them away] of massive proportions. All craters below a certain size will be completely obliterated. At progressively greater diameters, progressively less degraded craters will be visible. (Emphasis added.)
In other words, the larger craters, surrounded by higher walls, will survive longer than the smaller craters, surrounded by lower walls.
This analysis supports Velikovsky's concept regarding Mars. If the cratering event occurred on a surface with few, if any, craters, the population curves for craters would not fit the overall population curve because craters were not produced slowly, over time, but by a short, sudden catastrophic event.
Instead of acknowledging that a cratering catastrophe occurred, certain scientists suggest that, at a certain point in Martian history, nearly all the craters were completely removed by an erosion catastrophe. Mutch and his colleagues continue:
In an attempt to see if the crater data places any constraints on the cratering rate, [K L.] Jones demonstrates [K. L. Jones, "Evidence for an Episode of Crater Obliteration Intermediate in Martian History, Journal of Geophysical Research 79 (1974): 3917-3931.] that, under a set of specific, plausible conditions, the observed distribution could have resulted from a specific model in which an erosional episode with an intensity 100 times the background value occurred four fifths of the way through planetary history [about 920 million years ago]. When the distribution of morphologic types are compared with the actual values, a general coincidence is observed. Both [Clark R.] Chapman and [K. L.] Jones examine the uniqueness of their solution. Jones, in particular, concludes that the existence of a period of enhanced erosion is unavoidable. However, the position of that period of absolute time is uncertain. 
If, as the evidence suggests, Mars experienced an erosion catastrophe about a billion years ago in which the erosion rate became 100 times greater than the present rate, some plausible explanation is required. Carl Sagan's present, calculated erosion rate is 10 kilometers (6.2 miles) every 100 million years.  That is, his erosion rate will remove 100 feet of material from Mars in 300,000 years. At 100 times that rate, 10,000 feet of material will be eroded in 300,000 years. What inevitably follows is that the valleys of all the river systems would also be obliterated!
What must also follow is that, after removing all evidence of the river systems when their flowing water is gone, the river systems must be replaced! In order to do this on a planet which had long ago lost nearly all the volatiles, such as water vapor and other gases, is to find a plausible way to get them to return in sufficient amounts so as to recreate the atmospheric conditions which will allow water to once again flow on Mars' surface. This is impossible. As Bruce Murray, formerly of the California Institute of Technology, points out: "If the [river] channels were created by rainfall, it would seem that one must postulate two miracles in series: one to create the earth-like atmosphere [on Mars] for a brief epoch and another one to destroy it."  I believe that four miracles occurred on Mars: the first to create an atmosphere on Mars while it was outside the Continuously Habitable Zone and a rainfall whose runoff generated streams with dendritic systems; the second to remove the water and cause an erosion catastrophe which deleted all the craters and evidence of streams on Mars; the third to replace all the water and reproduce streams on Mars while it is still outside the CHZ; and the fourth to remove all the water again. The fourth miracle had to have occurred within the last few thousand years.
The erosion rate indicates that Mars was in the Continuously Habitable Zone recently. With respect to the Earth, the erosion rate indicates that the Earth should have developed a runaway greenhouse effect long ago. Using Carl Sagan's erosion rate, the river system topography would have been eroded away long ago. While Sagan and others have earnestly been attempting to create impossible scenarios to halt erosion on Mars and Venus to no avail, the dilemma remains. Eric Burgess sums up the situation:
Most generally accepted models of how the Sun has evolved since its formation require the assumption that the luminosity of the Sun has gradually increased. This leads to some major questions about the evolution of terrestrial planets. While a low luminosity in past ages might have allowed Venus to possess an ocean and have a relatively mild climate similar to that of Earth today, the problem remains of explaining how the Earth avoided becoming a deep-freeze planet; it receives only about half the solar radiation received by Venus. The temperature of Earth should have been well below freezing....
The problem with Mars is even more difficult to resolve. Today, Mars is a frozen world, yet, in times past, large quantities of liquid water must have flowed across its surface to sculpt the erosional features seen today. Yet, at the time of a lower solar luminosity, Mars would be expected to be much colder than today. 
The present temperature range on Mars today is roughly "[13°C] above zero to [93°C] below, depending on latitude and time of day";  or [52 ° F] to [-106°F]; or 286 K to 160 K. If we reduce these temperatures by 35%, the high day temperature on Mars drops to 186 K (-67° C or -152.6' F), which would indicate the need for a miracle to heat up Mars, specially since the low night temperature drops to -149°C or -236.2°F or 124 K.
This evidence absolutely precludes ancient Mars, at its present distance from the Sun, from ever having liquid water flowing on its surface. I suggest that the only plausible solution to this problem is for the scientific community to bite the bullet and face the possibility that, for Mars to have had liquid water flowing copiously for eons over its surface until the present, it needs to have been much closer to the Sun than it presently is. For those who detest the idea of recent solar system instability and wish to maintain Mars in its present orbit, I suggest that they must explain the dilemma posed by the Continuously Habitable Zone.
As T. H. Huxley once remarked to Herbert Spencer, theirs is "a beautiful theory, killed by a nasty, ugly little fact."
The penchant for developing beautiful theoretical models of the physical world which ignore critical aspects of reality that are purported to be explained ... brings to mind a dictum eloquently phrased by Roger S. Jones in Physics as Metaphor (New York, 1982): "The acid test of any scientific theory is, first and foremost, its agreement with the facts of the physical world. It is empiricism, not aesthetics, that is the backbone of science. Any theory, no matter how beautiful, will be rejected as soon as it is found incapable of corroborating the facts of nature (p. 207)." 
The fact that Ellenberger ignores in his presentation of the Continuously Habitable Zone is that for water to flow on Venus, the Earth and Mars at the same time requires that these planets not be in their current orbits since the beginning of the solar system. No amount of playing with this evidence will save appearances. Ellenberger needs more epicycles to support his idol. So as to salvage their theory of solar system stability, Ellenberger and other establishment scientists are hiding behind rhetoric, not evidence.
Rhetoric, as a response, is no response. Typical of this is Barry Evans' explanation:
[It is] tempting to think the reason [Mars has no water] is simply that Mars orbits farther out than we do, but the distance from the Sun turns out to be a red herring. To illustrate this point, consider two facts: one, Venus receives twice as much solar radiation as [the] Earth, yet it actually retains less solar energy than [the] Earth does (because its sulfuric acid clouds reflect 80% of sunlight before it reaches the surface); two, 4 billion years ago, when the Sun's heat was 30% less than it is now, [the] Earth had liquid water in abundance--and so did Mars judging from the Viking photo. It seems [that] distance from the Sun [does not] have much to do with it. Not all the questions regarding this problem are resolved. Rhetoric is the poorest excuse for scientific analysis. The fact that Mars has had water flowing on its surface does not agree with the facts of the physical world or with a stable solar system. The scientists are not using empiricism as a backbone to explain this scientifically. Their theory is neither "beautiful," nor accurate but is still not rejected, even though it cannot corroborate the facts of nature. Theirs is but a beautiful theory, killed by many ugly large facts.
 C. Leroy Ellenberger (A), "Still Facing Many Problems (Part 1)," KRONOS X: 1 (Fall 1984): 91-92.
 Su-Shu Huang (A), "Occurrence of Life in the Universe," American Scientist 47 (September, 1959): 397-402 and Su-Shu Huang (B), "Life Outside the Solar System," Scientific American 202: 4 (April, 1960): 55-63.
 Stephen H. Schneider and Stanley L Thompson, "Cosmic Conclusions from Climatic Models: Can They Be Justified?" Life in the Universe, ed. John Billingham (Cambridge, Massachusetts, 1982), p. 130.
 Ellenberger (A), op. cit., p. 92.
 Charles Ginenthal (A), "Oberg's Unscientific Method," The Velikovskian I: 4 (1993): 24-77 and George R. Talbott, "Checking the Checkered Checker," The Velikovskian I: 4 (1993): 78-81.
 Michael H. Hart (A), "The Evolution of the Atmosphere of the Earth," Icarus 33 (January, 1978): 23-39 and Michael H. Hart (B), "Habitable Zones About Main Sequence Stars," Icarus 37 (January, 1979): 351-357. Also see KRONOS X: 1 (Fall 1984): 91 for other citations.
 Roger K. Ulrich, "Solar Neutrinos and Variations in the Solar Luminosity," Science 190 (November 14, 1975): 619-624.
 James B. Pollack (A), "A Climate Change on the Terrestrial Planets," Icarus 37 (1979): 526.
 Carl Sagan and George Mullen, "Earth and Mars: Evolution of Atmospheres and Surface Temperatures," Science 177 (July 7, 1972): 52-56.
 James K. Pollack (B), "Atmospheres of the Terrestrial Planets," The New Solar System, eds. J. Kelly Beatty and Andrew Chaikin, 3rd ed. (New York, 1990), p. 103.
 Ann Henderson-Sellers and A. J. Meadows, "Surface Temperature of Early Earth," Nature 270 (December, 1977): 589-591.
 Tobias Owen, Robert D. Cess and V. Ramanathan, "Enhanced CO2 Greenhouse to Compensate for Reduced Solar Luminosity on Early Earth," Nature 277 (February, 1979): 640-641.
 William W. Rubey, "Geologic History of Sea Water," The Origin and Evolution of Atmospheres and Oceans, eds. Peter J. Brancazio and A. G. W. Cameron (New York, 1964), p. 2. See also the same paper in the Bulletin of the Geological Society of America 62 (1951): 1111.
 Everly Driscoll, "Mariner's Intriguing Evidence of a Formerly Watery Mars," Science News 103 (March 10, 1973): 156.
 Carl Sagan et al., "Climate Change on Mars," Science 181 (September 14, 1973): 1045.
 Pollack (B), op. cit., p. 101.
 "New Notes," Sky & Telescope (March, 1994): 14.
 Clark R. Chapman, The Inner Planets (New York, 1977), pp. 37-39.
 Charles Ginenthal (B), Carl Sagan and Immanuel Velikovsky, (New York, 1990), pp. 197-212.
 David Morrison and Tobias Owen, The Planetary System (New York, 1988), p. 276.
 Thomas A. Mutch et al., The Geology of Mars (Princeton, New Jersey, 1976), p. 128.
 Ibid. P. 130
 Carl Sagan (A), "Mariner 9 Data Stir New Questions," Aviation Week and Space Technology (January 29, 1973): 61.
 Richard S. Lewis, From Vineland to Mars (New York, 1976), p. 370.
 Eric Burgess, Venus, An Errant Twin (New York, 1985), p. 135.
 Peter Cattermole, Mars, the Story of the Red Planet (London, England, 1992), p. 13.
 C. Leroy Ellenberger (B), "Still Facing Many Problems (Part II)," KRONOS X: 3 (Summer 1985): 22.
 Barry Evans, The Wrong Way Comet and Other Mysteries of Our Solar System (Blue Ridge Summit, Pennsylvania, 1990), p. 81.