Surface temperatures during the early Hadean period were extremely high
the verdict
CONTESTED
contested - evenly split
refutedsupported
the weight of evidence
3 sources for · 3 against
Scientific literature presents conflicting evidence regarding Hadean surface temperatures, with some sources pointing to cold or clement surface environments while others indicate high thermal budgets and magma oceans.
Geochemical analysis of zircons older than 4 billion years, found in Early Archean metasediments at Jack Hills, Western Australia, provide insights into the nature of Hadean Earth. Oxygen isotopes have been interpreted as indicating that protoliths of magmas from which Hadean zircons crystallized were formed in the presence of water at or near Earth’s surface. Apparent crystallization temperatures of Hadean zircons cluster at 680 °C. Given the low porosity expected in rocks under anatectic conditions, dehydration melting of micas as the principal source of the melts from which these zircons crystallized can be ruled out. Instead, a regulated mechanism producing near minimum-melting conditions during the Hadean is inferred. Combined, these results have been interpreted to reflect chemical weathering and sediment cycling in the presence of liquid water shortly after Earth accretion. 176Hf/177Hf ratios of Hadean Jack Hills zircons show large heterogeneities indicating a major differentiation of the silicate Earth by 4.50 Ga. A possible consequence of this differentiation is the formation of continental crust of similar order to the present. Studies of mineral inclusions within Hadean zircons indicate their crystallization from hydrous, granitoid magmas at pressures greater than 6 kbars, implying low near-surface geothermal gradients which in turn suggests their origin in underthrust environments. Given general agreement that life could not have emerged until liquid water appeare
Abstract Constraining the surface environment of the early Earth is essential for understanding the origin and evolution of life. The release of cations from silicate weathering depends on climatic temperature and pCO2, and such cations sequester CO2 into carbonate minerals in or on the seafloor, providing a stabilizing feedback on climate. Previous studies have suggested that this carbonate‐silicate cycle can keep the early Earth's surface temperature moderate by increasing pCO2 to compensate for the faint young Sun. However, the Hadean Earth experienced a high meteorite impactor flux, which produced ejecta that is easily weathered by carbonic acid. In this study, we estimated the histories of surface temperature and ocean pH during the Hadean and early Archean using a new model that includes the weathering of impact ejecta, empirically justified seafloor weathering, and ocean carbonate chemistry. We find that relatively low pCO2 and surface temperatures are probable during the Hadean, for example, at 4.3 Ga, log10(pCO2) (in bar) is −2.21−2.54+3.01 [2σ] and temperature is 259.2−14.4+84.1 [2σ] K. Such a low pCO2 would result in a circumneutral to basic pH of seawater, for example, 7.90−1.69+1.21 [2σ] at 4.3 Ga. A probably cold and alkaline marine environment is associated with a high impact flux. Hence, if there was an interval of an enhanced impact flux, that is, Late Heavy Bombardment, similar conditions may have existed in the early Archean. Therefore, if the origin of lif
Mobile-lid tectonics is a first-order feature characterizing the modern Earth, yet its origins remain enigmatic due to a scarcity of ancient terrestrial materials. Detrital zircons provide the most complete archive of Earth’s early crust and preserve the only record extending beyond ~4.0 Ga. Here, we combine U XANES oxybarometry with U-Pb and trace element analysis to investigate the igneous cores and metamorphic rims of Hadean–Archean zircon from the Jack Hills, Australia. Igneous cores record consistent, moderately oxidized magma conditions (FMQ-1 to +1), challenging notions of a highly redu
Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. The first crust was mafic and it internally melted repeatedly to produce the felsic rocks that crystallized the Jack Hills zircons. This crust was destabilized during late heavy bombardment. Plate tectonics probably started soon after and had produced voluminous continental crust by the mid Archean, but ocean volumes were sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites to host the earliest living communities and for the evolution of key enzymes. Evidence from the Isua Belt, Greenland, suggests life was present by 3.8 Gya, and by the mid-Archean, the geological record both in the Pilbara in Western Australia and the Barberton Greenstone Belt in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By the late Archean, oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.
Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt, and granite, ∼1300, ∼1120, and ∼950 °C, respectively. At less than half their T solidi, rocky materials existed as thin lithospheric slabs in the near-surface Hadean Earth. Stagnant-lid convection may have occurred initially but was at least episodi
Abstract During Solar System condensation, the early Earth formed through planetesimal accretion, including collision of a Mars-sized asteroid. These processes rapidly increased the overall thermal budget and partial fusion of the planet. Aided by heat supplied by radioactivity and infall of the Fe-Ni core, devolatilization and chemical-density stratification attended planetary growth. After the thermal maximum at ∼4.4 Ga, terrestrial temperatures gradually declined as an early Hadean magma ocean solidified. By ∼4.3–4.2 Ga, H2O oceans + a dense CO2-rich atmosphere blanketed the terrestrial surface. Near-surface temperatures had fallen well below the low-P solidi of dry peridotite, basalt, and granite, ∼1300, ∼1120, and ∼950 °C, respectively. At less than half their melting T, rocky materials existed as thin lithospheric platelets in the surficial Hadean Earth. Upper mantle stagnant-lid convection may have operated locally, but was rapidly overwhelmed by heat build-up-induced asthenospheric circulation, rifting and subduction, because massive heat transfer required vigorous mantle overturn in the early, hot planet. Bottom-up mantle overturn, involving abundant plume ascent, brought deep-seated heat to the surface. It decreased over time as cooling, plate enlargement, and top-down plate descent increased. Thickening, lateral extension, and contraction typified the post-Hadean lithosphere. Geologic evolutionary stages included: (a) ∼4.5–4.4 Ga, the magma ocean solidified, genera
Everything we examined (7) — 6 independent sources
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