Venus evolution

Kaula W. M. (1999) Constraints on Venus evolution from radiogenic argon. Icarus 139, 32-39. 

The combination of forces that caused these changes is still in question but it involves the stability of the climate. The climate has fluctuated between limits of plus or minus 15°C (27°F) for hundreds of millions of years. These limits are large enough to have a major influence on species extinction and evolution. A runaway greenhouse effect is thought to have changed Venus where the oceans boiled. 

This co-evolution of life, atmospheric carbon dioxide and oxygen levels, and a relatively moderate climate (compared with other planets) make Earth unique. Earth has far less atmospheric carbon dioxide than Mars and Venus, neighboring planets that were formed at about the same time. The atmospheres of both Mars and Venus are made of more than 95% carbon dioxide. On these planets, there are no photosynthesizing life forms to alter the levels of atmospheric carbon dioxide or to produce oxygen. 

Noble gases are most abundant in planetary atmospheres, although even there they are only minor components. They have been measured in the gas envelopes of Venus, Earth (of course), Mars, and Jupiter. We will consider their utility in understanding planetary differentiation and atmospheric evolution shortly, but first we will focus on their rather miniscule abundances in meteorites and other extraterrestrial materials. 

Atmospheres are a natural consequence of the origin and evolution of planets. If planets are of sufficient size, they may have captured some nebular gas while they formed. Accretionary and radioactive heating can also release gases that were brought into the planet in solid carriers. The atmospheres of Venus, Earth, and Mars are composed of the same gases (C02, N2, H20, 02), but in markedly different amounts and proportions, reflecting their different evolutionary histories. For example, the rise of life on Earth... 

The recent advances in modem technology continue to open new opportunities for the observation of chemical reactions on shorter and shorter time scales, at higher and higher quantum numbers, in larger and larger molecules, as well as in complex media, in particular, of biological relevance. As an example of open questions, the most rapid reactions of atmospheric molecules like carbon dioxide, ozone, and water, which occur on a time scale of just a few femtoseconds, still remain to be explored. Another example is the photochemistry of the atmospheres of nearby planets like Mars and Venus or of the giant planets and their satellites, which can help us to understand better the climatic evolution of our own planet. 

Earth and Mars clearly contain H2O. Venus s atmosphere is very dry, and composed mainly of CO2, but the high D/H ratio of the small amount of water present suggests Venus was once much wetter than today (Zahnle 1998). Mercury is perhaps too small and too close to the Sun to have acquired and retained water. Water may have been present in much of the material that accreted to form the Earth. Small amounts of water may have been adsorbed onto dust grains at 1 AU by physisorp-tion or chemisorption (Drake 2005). Once Jupiter formed, substantial amounts of water could have been delivered to the growing Earth in the form of planetesimals and planetary embryos from the Asteroid Belt (Morbidelli et al. 2000). It is also possible that Earth lay beyond the snowline at some point during the evolution of the solar nebula (Chiang et al. 2001) so that local planetesimals contained ice. 

Other books of interest include Lewis and Prinn (1984), which emphasizes the use of observational data for understanding the origin, evolution, and present-day chemistry of planetary atmospheres. Krasnopolsky (1986) focuses on chemistry of the atmospheres of Mars and Venus. He also reviews the atmospheric composition, thermal structure, and cloud measurements by the Soviet Venera and Vega missions. Chamberlain and Hunten (1987) is the classic... 

Yung Y. L. and DeMore W. B. (1982) Photochemistry of the stratosphere of Venus implications for atmospheric evolution. Icarus 51, 199-247. 

Kasting J. F. (1988) Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus. Icarus 74, 472-494. 

Kaula W. M. (1990) Venus a contrast in evolution to Earth. Science 247, 1191-1196. 

While considerations of the origin of planetary noble gases have been predominantly focused on those presently found in the atmosphere, noble gases still within the Earth provide further constraints about volatile trapping during planet formation. A wide range of noble-gas information for the Earth s mantle has been obtained from mantle-derived materials, and indicates that there are separate reservoirs within the Earth that have distinctive characteristics that were established early in Earth history. These must be included in comprehensive models of Earth volatile history. Also, data are now available for the atmospheres of both Venus and Mars, as well as from the interior of Mars, so that the evolution of Earth volatiles can be considered within the context of terrestrial-planet formation across the solar system. 

Venus. Venus is characterized only by the immensely valuable but still incomplete and relatively imprecise reconnaissance data from the Pioneer Venus and Venera spacecraft missions of the late 1970s. Additional in situ measurements, at precisions within the capabilities of current spacecraft instrumentation, are now necessary to refine atmospheric evolution models. Unfortunately, the possibilities of documenting the volatile inventories of the interior of the planet are more remote. A significant question that must be addressed is whether nonradiogenic xenon on Venus is compositionally closer to SW-Xe (as seen on Mars) or to the U-Xe that is seen on the Earth and so is expected to have been present within the inner solar system. Also, the extent of xenon fractionation will be an important parameter for hydrodynamic escape models if intense solar EUV radiation drove hydrodynamic escape on the Earth, it would also impact Venus, while losses from the Earth driven by a giant impact would not be recorded there. 

Would Venus evolve on Mars Bioenergetic constraints, allometric trends, and the evolution of life-history invariants Jeffrey P. Schloss... 

A comparison of the atmospheres of Earth and Venus can shed light on the processes of planetary evolution. Scientists tend to believe that the two planets were created with relatively similar structures. Hydrogen, helium, and other light gases present during their formation were probably blown away early in the history of both planets by solar radiation. The present-day atmospheres of both... 

Sources Adapted from Bruce Fegley, Jr., "Venus,"Table 6, in A. M. Davis, ed.. Treatise on Geochemistry. New York Elsevier, 2004, and David R. Williams, Preliminary Mars Pathfinder APXS Results," http //nssdc.gsfc.nasa.gov/ planetary/marspath/apxs table1. html. For more detailed information on terrestrial data, see Taylor, S. R.( and S. M. McLennan, 1985 The Continental Crust Its Composition and Evolution. Blackwell Scientific Publications, 1985. 

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