Gas-dust cloud

According to present-day concepts, our solar system was formed from a huge gas-dust cloud several light years across in a side arm of the Milky Way. The particle density of this interstellar material was very low, perhaps 108-1010 particles or molecules per cubic metre, i.e., it formed a vacuum so extreme that it can still not be achieved in the laboratory. The material consisted mainly of hydrogen and helium with traces of other elements. The temperature of the system has been estimated as 15 K. 

On the basis of results of absolute geochronology (based on determining certain isotopes of lead, uranium, thorium, potassium and argon in the oldest rocks), we can assume that the Earth was formed about 4.6 milliard years ago [1] from a protoplanetary gas-dust cloud. Hydrogen and helium were the essential gaseous components of its cloud (in accordance with current knowledge about the composition of the Universe). 

The initial gas-dust cloud reached an appreciable density and started to compress under the iirfluence of gravitational forces. 

In the process of compression, the sizes of the gas-dust cloud decreased, and the speed of its rotation increased the speeds of compression of the cloud parallel and perpendicular to its axis of rotation differed, which led to condensation of the cloud and the formation of a disk. 

At achievement of some limiting density, the dust particles started to collide with each other and the released kinetic energy of the compressing gas-dust cloud led to temperature growth, with the central region of the disk to heat up most intensely. 

Striking of a smear or thin coating of alloy on rusty steel with a hammer. The glancing impact of stainless steel, mild steel, brass, copper-heryllium hronze, aluminium copper and zinc onto aluminium smears on rusty steel can initiate a thermite reaction of sufficient thermal energy to ignite flammahle gas/vapour-air atmosphere or dust clouds. 

Air and natural gas are often used as a drilling fluid with no additives placed in the injected stream of compressed fluid. This type of drilling is also often referred to as dusting because great dust clouds are created around the drill rig when no formation water was present. However, modern air and gas drilling operations utilize a spray at the end of the blooey line to control the dust ejected from the well. Figure 4-185 shows a typical site plan for air drilling operations. 

The second important source for the hydrosphere and the oceans are asteroids and comets. Estimating the amount of water which was brought to Earth from outer space is not easy. Until 20 years ago, it was believed that the only source of water for the hydrosphere was gas emission from volcanoes. The amount of water involved was, however, unknown (Rubey, 1964). First estimates of the enormous magnitude of the bombardment to which the Earth and the other planets were subjected caused researchers to look more closely at the comets and asteroids. New hypotheses on the possible sources of water in the hydrosphere now exist the astronomer A. H. Delsemme from the University of Toledo, Ohio, considers it likely that the primeval Earth was formed from material in a dust cloud containing anhydrous silicate. If this is correct, all the water in today s oceans must be of exogenic origin (Delsemme, 1992). 

Before 1985, six crystalline forms of carbon were known two forms of graphite, two forms of diamond, and chaoit and carbon (VI) discovered in 1968 and 1972, respectively. In addition a number of almost pure amorphous forms exist, such as polyacetylene (7.60) and cumulene (7.61) and recently a number of interesting nanostructured forms of carbon have been produced (Section 15.8). The year 1985 marked the discovery of the fullerenes, which represent the only truly pure molecular form of carbon, are produced under very extreme conditions as carbon vapour condenses in an atmosphere of an inert gas such as helium. Harold Kroto s interest in this chemistry originated with microwave spectroscopic studies of the atmosphere of stars and interstellar dust clouds. Kroto wanted to try to reproduce in the laboratory spectra of carbon... 

Let s talk about the varieties of stars in the heavens. In a nutshell, stars are different because the gas and dust clouds from which they emerge have different masses and densities. However, if two stars emerge with the same initial mass and chemical composition, their evolution and eventual fates will be the same. ... 

Stars form from collapsing interstellar gas and dust clouds. Interstellar dust also provides the raw material from which planets form. Under favorable conditions, i.e. low temperatures, the interstellar dust may survive processing in protoplanetary disks and later planetary metamorphism, e.g. in asteroids and comets. By far the... 

Fig. 10. The dust clouds Barnard 68 and 72, photographed by B. J. Bok (private communication at the 90-inch reflector of the Steward Observatory, Tucson, Arizona. These two dense clouds composed of dust and gas are seen projected against the great star cloud in Sagittarius... 

Fig. 11. The horsehead nebula, another dust cloud, seen projected against an HII region, i.e. an extended ionized cloud of interstellar gas...

The solar system accreted from a dust cloud, formed after a supernova explosion. From this primitive solar nebula condensed the Sun and the planets. Some of the oldest objects in the solar system yet found are Ca-Al-rich inclusions in meteorites, —4.566 Ga old (Allegre et al, 1995). It is possible that these grains predate the solar nebula and may have been formed in the expanding envelope of the supernova explosion (Cameron, 2002). 

Properties Colorless gas (or liquid) sharp, intensely irritating odor lighter than air easily liquefied by pressure. Bp -33.5C, fp -77C, vap press of liquid 8.5 atm (20C), sp vol 22.7 cu ft/lb (70C), d (liquid) 0.77 at 0C and 0.6819 at bp. Very soluble in water, alcohol, and ether. Autoign temp 1204F (650C). Combustible. Note Ammonia is the first complex molecule to be identified in interstellar space. It has been observed in galactic dust clouds in the Milky Way and is believed to constitute the rings of the planet Saturn. 

---