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Milestones in Early Evolution

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Abstract

During much of its early history Earth was dominated by an oxygen -poor, CO2+CO+methane -rich atmosphere, with several thousand to tens of thousands ppm CO2, inducing high-temperature low-pH acid ocean waters, extending beyond submarine fumaroles. Compensation of the low early solar radiation by the high greenhouse gas levels and the low albedo due to low continent/ocean ratio allowed presence of liquid water at the surface. The high water temperature resulted in little sequestration of CO2 accumulated in the atmosphere from episodic volcanism, impact cratering , metamorphic release of CO2, dissociation of methane from sediments and microbial activity. The low-oxygen levels of the Archaean hydrosphere limited marine life to extremophile cyanobacteria and, locally, photosynthesizing stromatolites, with limited release of oxygen about 3.5–3.4 Ga. Temperatures declined with the development of continental cratons and recycling of crustal material through the mantle in the Proterozoic and the Phanerozoic, including lowering of oceanic salinity due to sequestering of evaporite deposits in continental settings. Microbial methanogenesis involves reactions of CO2 with H2 or acetate (CH3CO 2 ) produced from fermentation of photosynthetically produced organic matter. An overall increase with time in δ18O, shown by terrestrial sediments, reflects a long term recycling of cold crustal materials through the mantle. Long-term cooling of the atmosphere and hydrosphere was related to an overall intermittent temporal decline in atmospheric CO2, as shown by plant leaf pores. An abrupt disappearance of positive sulphur (MIF-S ) anomalies at ~2.45 Ga suggests atmospheric enrichment in oxygen and development of an ozone layer related to progressive photosynthesis by algal activity. The origin of banded iron formations is interpreted in terms of microbial oxidation of ferrous (Fe+2) to ferric (Fe+3) iron under oxygen -poor atmospheric and hydrospheric conditions on the early Earth and direct chemo-lithotropic or photo-ferrotropic oxidation of ferrous to ferric iron. A biological significance of dolomite is corroborated by experimental studies that indicate precipitation of low-temperature dolomite in sedimentary systems and interstices of pillow lava under unoxidizing conditions and microbial mediation.

Orbits

When my being spirals inwards

Thoughts in my brain keep whirling

Intelligent mind-spinning electrons

Flee rotating black holes’ fatal pull

Eject energy torches light years away

Call me to pray amidst a stone haven circle

I scan the sky for the night-sailing moon

Circling Earthan ecliptic plane’s pilgrim

Live child of the Sun’s stony rings

Tells me a future already carved

In magical rings of galactic cathedrals

The Milky Way’s slow turning wheel

That somewhere, sometime

A new life cycle will sprout.

(Andrew Glikson)

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Notes

  1. 1.

    BioMed Central Public Release: 26-Jan-2004. Oxygen triggered the evolution of complex life forms. https://www.eurekalert.org/pub_releases/2004-01/bc-ott012204.php.

  2. 2.

    Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

  3. 3.

    Organic-sedimentary structures predominantly accreted by sediment trapping, binding and/or in situ precipitation as a result of the growth and metabolic activities of benthic, principally prokaryotic, micro-organisms .

  4. 4.

    For the early Earth, models of stellar evolution predict a solar energy input to the climate system which is about 25% lower than today. This would result in a completely frozen world over the first two billion years in the history of our planet, if all other parameters controlling Earth’s climate had been the same. Yet there is ample evidence for the presence of liquid surface water and even life in the Archean (3.8–2.5 billion years before present), so some effect (or effects ) must have been compensating for the faint young Sun. A wide range of possible solutions have been suggested and explored during the last four decades, with most studies focusing on higher concentrations of atmospheric greenhouse gases like carbon dioxide, methane or ammonia .

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Correspondence to Andrew Y. Glikson .

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Glikson, A.Y. (2019). Milestones in Early Evolution. In: From Stars to Brains: Milestones in the Planetary Evolution of Life and Intelligence. Springer, Cham. https://doi.org/10.1007/978-3-030-10603-4_2

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