Geological periods 23

The approach proposed to check the preservation of isotopic signals in fossil vertebrate bones and teeth is appropriate not only for Pleistocene cold and temperate areas, but also during geological periods before the... 

Formations from all geologic periods have been used for deep-well injection, but Paleozoic rocks are used for most injection zones (53%), followed by Tertiary-age formations (39%). Older Paleozoic rocks have been more frequently used for injection primarily because they tend to be more deeply buried. However, the more recent Tertiary-age Gulf Coast sediments are also very thick, and most injection in rocks of this age takes place there. 

If we are to describe evolution of the geological/biological ecosystem then we must have a way of estimating the time of appearance of various physical and chemical objects, including organisms. The best method we have of dating depends on studies of minerals. The so-called geological periods (Table 1.8), have to be obtained... 

Hadean A geological period of time from the formation of the Earth lasting for 800 million years, characterised by huge bombardment of the young planet. 

Urey, H. C., Cometary Collisions and Geological Periods, Nature 242, 32, 1973. 

For definitions of units, chemical composition of minerals, chemical formulae of molecules and time spans of geologic periods, see the Appendices. 

Labile markers are stable for shorter geological periods after diagenetic preservation. Group 2 compounds are stable for longer geologic periods. 

Geologic period Pb/U (g/g) Millions of years Today s accepted value... 

There are three significant possible effects when radiation interacts with matter (5,6). First, the radiation can interact with the nucleus and induce radioactivity as in the case of neutrons. Second, displacement of atoms can occur. This has happened in a number of uranium- and thorium-containing minerals over geological periods. The outstanding example is zircon, which can contain over 10% Th and 2% U. The internal bombardment from these materials and their decay products over geological periods produces low or metamict zircon, where the disorder gives an amorphous state having a low density. 

COAL. Containing more than 50% (weight) and 70% (volume) of carbonaceous material, including Inherent moisture, coal is a readily combustible rock. Coal was formed from the compaction and induration of variously altered plant remains similar lo those found in peal. Coal was formed during earlier geological periods, the process of formation acting slowly over extremely long periods of lime. Coal is not a uniform substance, but reflects the conditions of its formation. These include ... 

Coal Formation in the United States. It is postulated that coal formed in the U.S. during three major geological periods. 

From initial deposition and burial under overlying sedimentary materials through succeeding geological periods, coal beds are continually subject to the action of ground water. Thus, some coal beds have developed a system of essentially vertical fractures—thin cracks, often filled with coatings of pyrite. calcile. kaolinite and other minerals deposited from ground water. Impurities from these veins lower the quality of the coal. 

Cretaceous A geologic period that lasted from about 144-65 million years ago. 

Coal deposits, usually called beds or seams, can range from fractions of an inch to hundreds of feet in thickness. Coals are found in all geologic periods from Silurian through Quaternary, but the earliest commercially important coals are found in rocks of Mississippian age (Carboniferous in Europe). Coals generally... 

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