The first 800 million years: Environmental models for early earth

Abstract

Space exploration has changed our views not only on the properties of celestial bodies and the interplanetary medium but also our perspective on the formation of such bodies, including the Earth. However, on few points do the new hetegonic insights approach certainty. More appropriately, they can be said to raise physically meaningful questions and to decrease the degrees of freedom allowable in any given scenario, which necessarily extends into the early history of the planetary crust, ocean and atmosphere. An attempt is made here to outline the basic schemes envisaged in modern studies of the origin of the Earth and the ramification of consequences for its early evolution that currently appear allowable and supported by observation.

The Astrobiology Primer v2.0

“…Also, the temperatures postulated for the actual origin of life vary, some hypotheses favoring a hot environment (Miller and Lazcano, 1995), others favoring a cold environment (Bada and Lazcano, 2002). The average temperature on prebiotic Earth may have been higher than it is today (Arrhenius, 1987), but this is a topic of current debate. Given the lower luminosity of the young Sun and uncertainties about the abundance of greenhouse gases and continental area at the time, it is also possible that Earth cooled down relatively quickly to lower temperatures after its formation (Sleep et al , 2001; Rosing et al , 2010; Pope et al , 2012).…”

Chemical remanent magnetization in synthetic magnetite

“…In its structure, alternating divalent and trivalent iron ions are separated and surrounded by hydroxyl ions, forming sheets separated by interlayers of negatively charged ions and water molecules (Figure 1). The mineral is metastable and slowly decays by electron transfer from the ferrous ions, with attendant decomposition of water to molecular hydrogen [Schrauzer and Guth, 1976;Arrhenius, 1987]. This topotactic transformation results in ferroferric spinel (magnetite).…”

Mixed-valence hydroxides as bioorganic host minerals

“…This is further enhanced by photochemical oxidation of the solid (Schrauzer and Guth, 1976;Arrhenius, 1987), similar to the reaction described for dissolved Fe 2÷ and [Fe(OH)2] ° (Cairns-Smith, 1982;Braterman et al, 1983;Mauzerall and Borowska, 1988). The conversion of green rust to magnetite is rapid in the presence of cyanide ion, and less rapid when ferrocyanide ion is introduced in the interlayer; both the ferroferricyanide product and the ferrocyanide substituted green rust could, in the Archean ocean, have formed reservoirs of concentrated cyanide of potential significance for production of hydrogen cyanide oligomers and derivatives such as nitrogen bases .…”

“…One m e m b e r of this group, Fe(2)Fe(3) hydroxide, is represented in nature by the green rust minerals and by their alteration products, magnetite and iron silicates. Because of the special significance of the Fe(2)Fe(3) h y d r o x i d e complexes in A r c h e a n ocean sedimentation (Arrhenius, 1984(Arrhenius, , 1986(Arrhenius, , 1987 and in reactions involving cyanides, p h o s p h a t e s and aldehydes, these ferroferric members o f the p y r o a u r i t e family o f minerals are being investigated in further detail and are discussed in a separate paper. A n extended study o f the interaction of…”