Earth geological history

The early period of the Earth s history, known geologically as the Hadean, is associated with huge bombardment of the surface of the planet by meteors and comets. The sequence of events in the Earth s formation is shown in Figure 7.3, starting with the Hadean. Any volatile materials on the surface of dust grains or planetesimals deposited on the Earth will be removed and become part of the atmosphere, or more generally the volatile component inventory of the planet. 

Magma types and their sources in the Earth s history. 2006. Moscow IGEM RAS. Parfenov, L.M., Popeko, L.I., Tomurtogoo, O. 1999. Problems of tectonics of Mongol-Okhotsk orogenic belt. Geology of the Pacific Ocean, 18, 24-43. 

Geochemists study chemical processes on and in the Earth as well as meteorites and samples from the other planetary bodies. In geochemical kinetics, chemical kinetic principles are applied to Earth sciences. Many theories in geochemical kinetics are from chemical kinetics, but the unique nature of Earth sciences, especially the inference of geological history, requires development of theories that are specific for geochemical kinetics. 

A popular method used to date rocks is the potassium-argon method. Potassium is abundant in rocks such as feldspars, hornblendes, and micas. The K-Ar method has been used to date the Earth and its geologic formations. It has also been applied to determine magnetic reversals that have taken place throughout the Earth s history. Another method used in geologic dating is the rubidium-strontium, Rb-Sr, method. Some of the oldest rocks on Earth have been dated with this method, providing evidence that the Earth is approximately 5 billion years old. The method has also been used to date moon rocks and meteorites. 

Global warming pressure groups would have the world believe that catastrophic changes in the earth s climate will occur without drastic limitations of carbon dioxide emissions—this in spite of the fact that the carbon dioxide levels in the earth s atmosphere have been much higher than today s for much of geological history. For example, as documented by the work of Berner,13 atmospheric carbon dioxide concentrations were some five 15... 

These are significant activities, that occur repeatedly over many cycles. According to Yariv and Cross during the geologic history of the earth more than 70% of weath-... 

Thinking about the Earth A History of Ideas in Geology (London Athlone, 1996). 

In their attempts to establish the geological history of the earth, geologists have made extensive use of radioactivity. For example, since 29 U decays to the stable 2gfPb nuclide, the ratio of Pb to fU in a rock can, under favorable circumstances, be used to estimate the age of the rock. 

On the basis of the data obtained Chukhrov et al. (1977) assume that in all epochs of the geologic history of the Earth, including the Proterozoic, iron was supplied to the sedimentary basins chiefly in the form of ferrihydrite, which either was converted to hematite (in the absence of organic matter) or was reduced by organic matter during diagenesis to siderite and iron silicates, as was assumed in the works by Strakhov (1960) and Plaksenko (1966). 

The problem of the formation of the Precambrian banded iron-formations (BIF), repeatedly the subject of discussion, continues to be pressing. The present interest in it is explained not only by the ever-increasing importance of iron cherts as economic ores, but also by the special position they occupy in the geologic history of the Earth. 

It is likely that the ancient crust of Mars is more mafic than the Earth s continental crust. Pervasive andesite may signal crustal fractionation, but the identity and significance of andesitic rocks is disputed. The martian crust is relatively more voluminous than the Earth s cmst, perhaps because it is not recycled. The cmst is characterized by high concentrations of incompatible hthophile elements, but fractionations are not as extreme as in terrestrial continental cmst, which has experienced repeated partial melting events over a protracted geologic history. 

SNC meteorites (Harper et al., 1995 Borg et al., 1997). This isotopic anomaly requires early differentiation of mantle and crust. Because hafnium and mngsten fractionated into silicate and metal, respectively, the short-lived Hf- W system can be used to determine that martian core formation occurred within —13 milhon years of the planet s accretion (Kleine et al., 2002 Yin et al., 2002). Correlation between Nd and isotope anomalies, as well as the initial Os/ Os ratios for martian meteorites (Brandon et al., 2000), indicate synchronous differentiation of core, mantle, and cmst (Figure 14). On Earth, core formation took substantially longer, convection has stirred the mantle sufficiently to erase any evidence of early isotopic heterogeneity, and cmst formation continues throughout geologic history. 

Harte B., Cox K. G., and Gurney J. J. (1975) Petrography and geological history of upper mantle xenoliths from the Matsoku kimberlite pipe. Phys. Chem. Earth 9, 477-506. 

Oceanic plateaus represent overthickened areas of oceanic crust (10-35 km), which appear to have formed as a result of decompression melting of a large mantle plume head, often (although not always) within 1 -2 Ma. Geological and geochemical evidence suggests that oceanic plateaus have formed throughout a considerable period of Earth s history. 

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