A cool early Earth

Valley, John W.; Peck, William H.; King, Elizabeth M.; Wilde, Simon A.

doi:10.1130/0091-7613(2002)030<0351:acee>2.0.co;2

Cited by 415 publications

(171 citation statements)

References 21 publications

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“…The presence and composition of the zircons also implies a surrounding rock from which it formed that was not as mafic as basalt, but rather more continental in nature, such as might have differentiated from the mantle in a tectonic setting equivalent to present-day Iceland (Valley et al 2002), in which large basaltic islands (submerged or exposed) enclosed small granitic masses (Halliday 2004a).…”

Section: Conditions In the Hadean With Respect To The Origin Of Lifementioning

confidence: 99%

Physical conditions on the early Earth

Lunine

2006

Phil. Trans. R. Soc. B

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The formation of the Earth as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions of these objects, facilitated by the gravitational perturbations associated with Jupiter. The Earth's inventory of water and organic molecules may have come from diverse sources, not more than 10% roughly from comets, the rest from asteroidal precursors to chondritic bodies and possibly objects near Earth's orbit for which no representative class of meteorites exists today in laboratory collections. The final assembly of the Earth included a catastrophic impact with a Mars-sized body, ejecting mantle and crustal material to form the Moon, and also devolatilizing part of the Earth. A magma ocean and steam atmosphere (possibly with silica vapour) existed briefly in this period, but terrestrial surface waters were below the critical point within 100 million years after Earth's formation, and liquid water existed continuously on the surface within a few hundred million years. Organic material delivered by comets and asteroids would have survived, in part, this violent early period, but frequent impacts of remaining debris probably prevented the continuous habitability of the Earth for one to several hundred million years. Planetary analogues to or records of this early time when life began include Io (heat flow), Titan (organic chemistry) and Venus (remnant early granites).

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Section: Conditions In the Hadean With Respect To The Origin Of Lifementioning

confidence: 99%

Physical conditions on the early Earth

Lunine

2006

Phil. Trans. R. Soc. B

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“…Evidence from ancient zircon minerals indicates that the Earth attained clement surface conditions within about 150 million years of the first solids condensing in the solar system (Valley et al 2002), perhaps less than 100 million years after the Moon-forming impact (Touboul et al 2007). Here I show that a water ocean may be obtained within that time period on the Earth (and similarly for super-Earths) through two primary mechanisms: First, enrichment of water in a solidifying magma ocean to the point that excess water is extruded onto the Earth's surface at the end of silicate mineral solidification.…”

Section: Introductionmentioning

confidence: 99%

Formation of early water oceans on rocky planets

Elkins-Tanton

2010

Astrophys Space Sci

103

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Terrestrial planets, with silicate mantles and metallic cores, are likely to obtain water and carbon compounds during accretion. Here I examine the conditions that allow early formation of a surface water ocean (simultaneous with cooling to clement surface conditions), and the timeline of degassing the planetary interior into the atmosphere. The greatest fraction of a planet's initial volatile budget is degassed into the atmosphere during the end of magma ocean solidification, leaving only a small fraction of the original volatiles to be released into the atmosphere through later volcanism. Rocky planets that accrete with water in their bulk mantle have two mechanisms for producing an early water ocean: First, if they accrete with at least 1 to 3 mass% of water in their bulk composition, liquid water may be extruded onto the planetary surface at the end of magma ocean solidification. Second, at initial water contents as low as 0.01 mass% or lower, during solidification a massive supercritical fluid and steam atmosphere is produced that collapses into a water ocean upon cooling. The low water contents required for this process indicate that rocky super-Earth exoplanets may be expected to commonly produce water oceans within tens to hundreds of millions of years of their last major accretionary impact, through collapse of their atmosphere.

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“…The oldest known terrestrial rocks are represented by the gneisses outcropping in Amitsoˆq and Isua (Greenland) that are dated between 3.82 and 3.85 Ga and by small enclaves of older (4.03 Ga) gneisses in Acasta, Canada (Martin, 2001). An older formation age of 4.4 Ga has been measured in the cores of a few detrital zircon crystals recovered from Jack Hill (Australia) Valley et al, 2002). On Earth, the period comprised between the end of the accretion and the first occurrence of terrestrial rocks is commonly referred to as the Hadean Eon (Harland et al, 1989).…”

Section: Discussion Of Zircon Datamentioning

confidence: 99%

“…Moreover, if the elevated mass accretion documented in the period around 3.9 Ga is considered to be the tail end of an extended period of collisions, the whole Moon should have accreted at about 4.1 Ga instead of 4.5 Ga (Ryder, 2002;Koeberl, 2004). On Earth, the oxygen isotopic signature (d 18 O) of the oldest known zircons (4.4 Ga) indicates formation temperatures compatible with the existence of liquid water (Valley et al, 2002). This argument seems contradictory with an extended period of intense collisions.…”

Section: Discussion Of Zircon Datamentioning

confidence: 99%

4. Building of a Habitable Planet

et al. 2006

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Abstract. Except the old Jack Hills zircon crystals, it does not exit direct record of the first 500 Ma of the Earth history. Consequently, the succession of events that took place during this period is only indirectly known through geochemistry, comparison with other telluric planets, and numerical modelling. Just after planetary accretion several episodes were necessary in order to make life apparition and development possible and to make the Earth surface habitable. Among these stages are: the core differentiation, the formation of a magma ocean, the apparition of the first atmosphere, oceans and continents as well as the development of magnetic field and of plate tectonics. In the same time, Earth has been subject to extraterrestrial events such as the Late Heavy Bombardment (LHB) between 3.95 and 3.8 Ga. Since 4.4-4.3 Ga, the conditions for pre-biotic chemistry and appearance of life were already met (liquid water, continental crust, no strong meteoritic bombardment, etc...). This does not mean that life existed as early, but this demonstrates that all necessary conditions assumed for life development were already present on Earth.

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A cool early Earth

Cited by 415 publications

References 21 publications

Physical conditions on the early Earth

Physical conditions on the early Earth

Formation of early water oceans on rocky planets

4. Building of a Habitable Planet

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