Evolution geological periods 21

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... 

Figure 2.3 The basic patterns of species evolution according to phyletic gradualism (left) and punctuated equilibria (right). In the last model, horizontal lines indicate that speciations took place in geologically brief periods, and the fact that letters do not change along vertical lines signifies that species remained unchanged for long geological periods of time.

The principal geological periods into which earth history has been divided (Table 1.1) have been established on the basis of the evolution of life forms recorded by fossils found in the successive... 

On a larger scale, landscape development reflects those mechanisms that expose bedrock, weather it, and transport the weathering products away. Present and past tectonism, geology, climate, soils, and vegetation are all important to landscape evolution. These factors often operate in tandem to produce characteristic landforms that presumably integrate the effects of both episodic and continuous processes over considerable periods of time. 

The geological sciences are involved in studying the naturally occurring materials of the earth and solar system (i) to understand the fimdamental processes of crustal formation on earth and solar system evolution, and (2) to evaluate the crustal materials of potential economic value to man. Prior to the 1930 s, analyses were carried out exclusively using classical analytical techniques, with detection limits on the order of o.oi-o.i % (mass fraction). The number of elements contained in any sample could be as extensive as the periodic table, but very few of these could be determined. The development of instrumental techniques revolutionized the analysis of geochemical samples, beginning in the 1930 s. 

Table 1.1 Atimefine of evolution demonstrates the tremendous expanse of geologic time compared to the period since humans evolved. The indicated times of evolutionary events are subject to change as new information is found. ...

The atmosphere, ocean, and biosphere leave their record in sedimentary rocks. It is likely that this record reflects both secular and cyclic evolutionary processes. The cyclic processes involve chemical mass transfer of materials in and out of global reservoirs like the atmosphere, ocean, and sedimentary rocks. If inputs and outputs of these reservoirs are nearly balanced so that over long periods of geologic time the mass and composition of the reservoirs remain constant, a quasi-steady state is maintained. Hand-in-hand with this cyclicity go changes in Earth s surface environment reflecting secular evolution of the planet, an aging process. 

Therefore the model of Chase and Perry, in which the geologic and isotopic data can be reconciled and which gives a quantitative estimate of the evolution, seems to be rather sound. Naturally, periodic fluctuations of S O caused by mass deposition of chemogenic carbonates, silicates, and silica in individual geologic epochs, and also by temperature variations, cannot be ruled out. 

Typical BIF are metamorphosed chemogenic cherty iron sediments, deposition of which was typical only of the Precambrian and ceased in subsequent geologic epochs. The formation of these rocks reflects a certain stage in the irreversible process of evolution of the Earth s crust, atmosphere, hydrosphere and biosphere. The period of intensive deposition apparently was preceded by a long period of accumulation of dissolved iron and silica in the waters of the original sedimentary basins. 

Whether a hydrocarbon accumulation that is no longer replenished from the source rock will persist through extended periods of geological time basically depends on the type of trap, the type of accumulated hydrocarbon and the geological and associated hydrodynamic evolution of the sedimentary basin since entrapment. 

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