Comets impacts

In a somewhat arcane context. Chapman and Morrison, in the scientific journal Nature, have provided a list of comparative risks of death in the United States (Table 15.4) from a number of causes. The purpose of their paper was to assess the hazard of an asteroid or comet impact on the earth. Such an event does not immediately come to mind when considering the safety of medicines, but according to their estimates the chances of being killed by an asteroid/comet impact are about the same as dying in an air accident, which... 

Gravitational stirring of icy planetesimals by the giant planets could have sent many comets careening into the inner solar system, providing a mechanism for late addition of water to the terrestrial planets. Comets impacting the Earth and the other terrestrial planets would have delivered water as ice (Owen and Bar-Nun, 1995 Delsemme, 1999), whereas the accretion of already altered carbonaceous chondrite asteroids would have delivered water in the form of hydroxl-bearing minerals (Morbidelli el al., 2000 Dauphas et al., 2000). 

Asteroid- or Comet-Impact Hypothesis of Tektite Origin. In Tektites, J. A. O Keefe, Ed. Chicago, 1963. 

Owen T. and Bar-Nun A. (1995a) Comets, impacts, and atmospheres. Icarus 116, 215-226. 

Owen T. and Bar-Nun A. (1995b) Comets, impacts, and atmospheres 11. Isotopes and noble gases. In Volatiles in the Earth and Solar System, AIP Conf. Proc. 341 (ed. K. A. Farley). American Institute of Physics Press, New York, pp. 123-138. 

Nevertheless, it may be useful to consider the Paleozoic and Mesozoic extinctions to be the result of two phenomena oceanic anoxia in the Paleozoic and asteroid-comet impact in the Mesozoic. 

NASA Ames Space Science Division. Asteroid and Comet Impact Hazards, The Torino Scale [cited March 12, 2003]. d]ttp //impact.arc.nasa.gov/torino/>. 

As briefly reviewed above, various types of apparatus have been used according to each experimental purpose, but few methods allowed for the collection of materials produced, without incotporating surrounding contamination. Recently, we developed a simplified system for the shock technique, which can be applied to any form of material and which enables us to recover and examine shocked products witliout contamination [134,135]. Furthermore, this system can be used at extremely low temperatures to simulate reactions in space such as those caused by icy comet impacts. In tlris section, we describe chemical reactions disclosed by the new technique developed in our laboratory. These studies provide us witli useful infonnation on the means of creating the organic compounds found in the cosmos. 

The crater of an ancient asteroid or comet impact lies long the Mexican coast. 

CONTEXT Formal charges in molecules, NMR chemical shifts, and chemical bond orders are all determined by the probability density of the electron in specific regions of space. Even in individual atoms, we can use the probability density close to the nucleus to distinguish one element from among many others in a rich mixture of compounds, such as soil. The interaction between the nucleus and the electron density near the nucleus is one probe that has been used to find evidence of prehistoric comet impacts on Earth and their possible role in mass extinctions. The Cretaceous-Tertiary (K-T) boundary is a visible layer in the earth s crust that divides the fossil record into the times before and after the dinosaurs. Roughly 65 million years ago, the K-T boundary was formed, and after that, no more dinosaurs. Physicist Luis Alvarez in 1980... 

Eucrites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta. Die meteorite Serra de Mag6, an eucrite, contains quartz veinlets. They are identical to crack-seaT quartz veinlets in terrestrial rocks, and are extraterrestrial and ancient because they pre-date a 4.40 Ga metamorphism. The quartz was likely deposited from liquid water solutions (as are terrestrial veins). Because there is no indication of internal (magmatic) water in the eucrite meteorites and thus in Vesta, the water from which the veinlet was deposited probably came from outside Vesta. By analogy with water ice deposits on the Moon and Mercury, Vesta and similar asteroids may have had (or now have) polar ice deposits, possibly remainders from comet impacts (Treiman et al., 2004 [339]). 

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