Origin and evolution of the Earth

The planets of our solar system probably formed from a disc-shaped cloud of hot gases, the remnants of a stellar supernova. Condensing vapours formed solids that coalesced into small bodies (planetesimals), and accretion of these built the dense inner planets (Mercury to Mars). The larger outer planets, being more distant from the sun, are composed of lower-density gases, which condensed at much cooler temperatures. 

As the early Earth accreted to something like its present mass some 4.5 billion years ago, it heated up, mainly due to the radioactive decay of unstable isotopes (Box 1.1) and partly by trapping kinetic energy from planetesimal impacts. This heating melted iron and nickel (Ni) and their high densities allowed them to sink to the centre of the planet, forming the core. Subsequent cooling allowed 

Elements are made from atoms—the smallest particle of an element that can take part in chemical reactions. Atoms have three main components protons, neutrons and electrons. Protons are positively charged, with a mass similar to that of the hydrogen atom. Neutrons are uncharged and of equal mass to protons. Electrons are about 1/1836 the mass of protons, with a negative charge of equal value to the (positive) charge of protons. 

Atoms are electrically neutral because they have an equal number (Z) of protons and electrons. Z is known as the atomic number and it characterizes the chemical properties of the element. 

The atomic weight of an atom is defined by its mass number and most of the mass is present in the nucleus. 

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Stevenson D.J., in Origin and Evolution of the Earth s Earliest Biosphere An Interdisciplinary Study, (ed. J.W. Schopf), Princeton Univ. Press, 1983, to be published. 

McDougall I. and Honda M. (1998) Primordial solar gas component in the Earth consequences for the origin and evolution of the Earth and its atmosphere. In The Earth s Mantle Composition, Structure, and Evolution (ed. 1. Jackson). Cambridge University Press, Cambridge, pp. 159-187. 

Jordan, T. H. 1981. Continents as a chemical boundary layer. In The Origin and Evolution of the Earth s Continental Crust. Transactions of the Royal Society of London, London, 301, 359-373. 

EUer JM, Kitchen N (2004) Hydrogen isotope evidence for the origin and evolution of the carbonaceous chondrites. Geochim Cosmochim Acta 68 1395—1411 EUer JM, Schauble E (2004) in earth s atmosphere. Geochim Cosmochim Acta 68 ... 

Margulis, L. Matthews, C. Haselton, A. Environmental Evolution. Effects of the Origin and Evolution of Planet Earth-, The MIT Press Cambridge. MA, 2000. 

The composition of the Earth s core is a fundamental issue in the study of the Earth. It is directly linked to the volatile element budget of the bulk Earth, the conditions and mechanisms of core formation, the nature and dynamics of coremantle interaction, and the origin and evolution of the geomagnetic field. 

The near solar-like Ne isotope compositions, the high Ar/ Ar ratios, and the non-atmospheric Xe/ Xe and Xe/ Xe in oceanic basalts also provide basic clues on the origin and evolution of the atmosphere. The atmosphere appears to have formed within the first 50-70 Ma of Earth s history, probably coincident with the period of terrestrial core formation (Halliday and Lee 1999). 

The Precambrian banded iron formations are huge, flat accumulations, ( V 500 km across and V 500 m thick) mainly of silica and iron minerals arranged in bands, present in the Precambrian cores of all continents They are the world s main ore of iron. The consensus is that they formed by precipitation out of shallow water bodies at earth s surface temperatures, and that somehow their origin appears to be tied to the composition and evolution of the earth s early atmosphere. Beyond this, everything else is controversial How did such extreme chemical winnowing take place over whole basins up to hundreds of kilometers across ... 

Lammer et al., 2008 [192] discussed the origin and evolution of Venus , Earth s, Mars and Titan s atmospheres from the time when the active young Sun arrived at the Zero-Age-Main-Sequence. Thermal and various nonthermal atmospheric escape processes influenced the evolution and isotope fractionation of the atmospheres and water inventories of the terrestrial planets efficiently. 

O Hara MJ (1968) The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4 69-133 O Nions RK, McKenzie D (1993) Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil Trans Royal Soc 342 65-77 Oversby V, Gast PW (1968) Lead isotope compositions and uranium decay series disequilibrium in reeent volcanic rocks. Earth Planet Sci Lett 5 199-206... 

Chyba CF, Sagan C (1997) Comets as a Source of Prebiotic Organic Molecules for the Early Earth. In Thomas PI, Chyba CF, Me Kay CP (Eds.) Comets and the Origin and Evolution of Life. Springer, Berlin Heidelberg New York, p 147 Chyba CF (2005) Science 308 962 de Bergh C (1993) Orig Life Evol Biosphere 23 12... 

C. De Duve, Vital Dust. The Origin and Evolution of Life on Earth, Perseus Books Group, 1995. 

Atmospheres are a natural consequence of the origin and evolution of planets. If planets are of sufficient size, they may have captured some nebular gas while they formed. Accretionary and radioactive heating can also release gases that were brought into the planet in solid carriers. The atmospheres of Venus, Earth, and Mars are composed of the same gases (C02, N2, H20, 02), but in markedly different amounts and proportions, reflecting their different evolutionary histories. For example, the rise of life on Earth... 

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