Earths Unique Atmosphere

Consider first the natural atmosphere. In this context the term natural refers to an atmosphere untouched by human activity. That does not mean, though, that before there were humans there was no air pollution. Pollution can also have natural causes we just were not around to experience it. 

Not all air pollution is anthropogenic. Volcanoes spew noxious gases (especially SO ) into the atmosphere. Decaying vegetation in marshes and swamps emit methane (CH ) and hydrogen sulfide (HjS) into the atmosphere. Violent winds can kick up dust and sand storms. 

Before humans came on the scene, there were many gases in Earth s atmosphere N, O, Ar, water vapor, CO, CO, NO, NO, SO, SO3, O3, HNO3, H SO, He, Ne, Kr, Xe, Rn, and many organic compounds that resulted from the presence of living organisms on Earth. 

Some of these gases—CO, NO, SO, HNO3, and H SO especially—are classified from a human point of view as air pollutants. In addition, even a natural atmosphere contains soot, particulate matter, and aerosols. 

Earth s atmosphere is unique in our solar system. Other planets and some moons have an atmosphere, but Earth s atmosphere is the only one of which we are aware that can support life as we know it. (Life may exist elsewhere in the solar system—and the search for extraterrestrial life is part of many space missions—but the fact remains that the presence of life outside of Earth s biosphere has not been discovered.) 

---

Many of the processes responsible for isotope fractionations in the Earth s atmosphere may also occur in the atmospheres of other planetary systems, such as the atmospheric escape of atoms and molecules to outer space. Likely unique to Earth are isotope fractionations related to biological processes or to interactions with the ocean. One aspect of atmospheric research which has great potential for the application of stable isotope investigations is the study of anthropogenic pollution. 

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. 

The accurate determination of rate constants for the reactions of 19F atoms is often hampered by the presence of reactive F2 and by the occurrence of side reactions. The measurement of the absolute concentration of F atoms is sometimes a further problem. The use of thermal-ized 18F atoms is not subject to these handicaps, and reliable and accurate results for abstraction and addition reactions are obtained. The studies of the reactions of 18F atoms with organometallic compounds are unique, inasmuch as such experiments have not been performed with 19F atoms. In the case of addition reactions, the fate of the excited intermediate radical can be studied by pressure-dependent measurements. The non-RRKM behavior of tetraallyltin and -germanium compounds is very interesting inasmuch as not many other examples are known. The next phase in the 18F experiment should be the determination of Arrhenius parameters for selected reactions, i.e., those occurring in the earth s atmosphere, since it is expected that the results will be more precise than those obtained with 19F atoms. 

The controls on the atmosphere s operation (Walker, 1977) are complex and poorly understood, yet have been robust enough to keep the planet habitable over 4 Ga. The greenhouse effect adds —33 °C to the temperature (Lewis and Prinn, 1984). Without the atmosphere, the temperature of the planet would be — 18 °C with the atmosphere it is a pleasant - -15 °C. But is the control pure inorganic chance, or is it somehow implemented because the Earth, uniquely, is inhabited And when did the control begin ... 

Milagro is a unique TeV gamma-ray observatory capable of continuously monitoring the overhead sky. The directions of gamma-rays impacting the earth s atmosphere are reconstructed through the detection of air-shower particles that reach the earth. The shower particles are detected with a 60m x 80m... 

Scientists recognized that an element s spectrum is like human fingerprints just as each person has unique fingerprints, each element in the periodic table has a unique spectrum. The spectrum of a compound is simply a combination of the spectra of the elements in that compound. The uniqueness of spectra makes them powerful analytical tools in the identification of the elements found in minerals, in biological samples, in Earth s atmosphere, and in the atmospheres of stars. Although much... 

THE RICHNESS OF LIFE ON Earth, represented in the chapteropening photograph, is, as far as we know, unique. Earth s atmosphere, the energy received from the Sun, and the abundance of water on our planet are all features currently believed to be necessary for life. 

As the temperature of the blackbody increases, its colour changes as evident in Figures 5 and 6. The colour of a blackbody is thus uniquely dependent on its temperature. Real sources such as tungsten lamps that have spectral distributions approximating those of blackbodies can be assigned a colour temperature at which the spectrum most nearly overlays that of the blackbody. Outside the Earth s atmosphere, the Sun can, for example, be approximated as a blackbody at 6200 K, which is, then, the Sun s colour temperature. 

The Earth is a highly unusual planet because life did evolve on it and it thrived to the extent that the surface and atmosphere of the planet were greatly modified. The Earth is unique in this respect relative to all known astronomical bodies (Taylor, 1999). The Earth s location, composition, and evolutionary history are all significant factors in the planet s success in nurturing life. Critical factors include its temperature, its atmosphere, its oceans, its long-term stability and its "just right" abundance of water and other light element compounds. 

Liquid water is difficult to find in the universe. Scientists have found frozen ice in places such as Mars and gaseous water vapor in atmospheres such as that on Venus. However, no one has been able to find liquid water anywhere other than on Earth. Water is the only natural substance that is found in all three states of matter (solid, liquid, and gas) at the temperatures normally found on Earth. By exploring a few of the properties of water, you will discover what makes water unique. 

Water. Water generally occurs in air in low or relatively low concentrations, mostly in the form of atmospheric moisture. Its importance cannot, however, be overemphasized, since atmospheric moisture, unique to the surface of the earth, is a determining factor in the water cycle (see below) and in living and other processes. Moisture is, therefore, one of the most important and probably the most relevant atmospheric components for the majority of living processes. 

In 1994, a unique incident occurred the impact of the Shoemaker-Levy comet on the Jovian atmosphere. Die strong gravitational field of Jupiter caused the comet to break up before it could enter the atmosphere, and the parts of the comet crashed separately into the atmosphere one after the other. This unique spectacle was observed by many observatories and also by the Galileo spacecraft and the Hubble telescope. It led to the discovery of yet another phenomenon the most intensive aurora effects in the solar system, observed at Jupiter s poles. Astronomers assume that the energy for these comes from the planet s rotation, possibly with a contribution from the solar wind. This process differs from that of the origin of the aurora on Earth, where the phenomenon is caused by interactions between the solar wind and the Earth s magnetic field. 

The planets nearest the Sun have a high-temperature surface while those further away have a low temperature. The temperature depends on the closeness to the Sun, but it also depends on the chemical composition and zone structures of the individual planets and their sizes. In this respect Earth is a somewhat peculiar planet, we do not know whether it is unique or not in that its core has remained very hot, mainly due to gravitic compression and radioactive decay of some unstable isotopes, and loss of core heat has been restricted by a poorly conducting mainly oxide mantle. This heat still contributes very considerably to the overall temperature of the Earth s surface. The hot core, some of it solid, is composed of metals, mainly iron, while the mantle is largely of molten oxidic rocks until the thin surface of solid rocks of many different compositions, such as silicates, sulfides and carbonates, occurs. This is usually called the crust, below the oceans, and forms the continents of today. Water and the atmosphere are reached in further outward succession. We shall describe the relevant chemistry in more detail later here, we are concerned first with the temperature gradient from the interior to the surface (Figure 1.2). The Earth s surface, i.e. the crust, the sea and the atmosphere, is of... 

Knowledge of the 90 chemical elements and their properties in compounds led to the construction, by man, of a unique table of elements, the Periodic Table, of 18 Groups in six periods in a pattern fully explained by quantum theory, described in Chapter 2. There is then a huge variety of chemical combinations possible on the Earth and limitations on what is observable are related to element position in this Table. It also relates to the thermodynamic and/or kinetic stability of particular combinations of them in given physical circumstances (Table 11.3). The initial state of the surface of the Earth with which we are concerned was a dynamic water layer, the sea, covering a crust mainly of oxides and some sulfides and with an atmosphere of NH3, HCN, N2, C02(C0, CH4), H20, with some H2 but no 02. This combination of phases and their contents then produced an aqueous solution layer of particular components in which there were many concentration restrictions between it and the components of the other two layers due to thermodynamic stability, equilibria, or kinetic stability of the chemicals trapped in the phases. It is the case that equilibrium... 

The rate of photolysis, J, depends on the absorption cross-section, a, the number density, the scale height and the angle, all of which are unique properties of a planetary atmosphere. For the Earth and the Chapman mechanism for ozone the O3 concentration maximum is 5 x 1012 molecules cm-3 and this occurs at 25 km, shown in Figure 7.12, and forms the Chapman layer structure. 

Most of the water on Earth s surfece is in the ocean relatively little is present in the atmosphere or on land. Because of its chemical and physical properties, this water has had a great influence on the continuing biogeochemical evolution of our planet. Most notably, water is an excellent solvent. As such, the oceans contain at least a little bit of almost every substance present on this planet. Reaction probability is enhanced if the reactants are in dissolved fitrm as compared with their gaseous or solid phases. Many of the chemical changes that occur in seawater and the sediments are mediated by marine organisms. In some cases, marine organisms have developed unique biosynthetic pathways to help them survive the environmental conditions fitimd only in the oceans. Some of their metabolic products have proven useful to humans as pharmaceuticals, nutraceuticals, food additives, and cosmeceuticals. 

---