Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earth

Ershov, B.G.

Автор: Ershov Boris G.
Журнал: Precambrian Research
Том: 406
Год издания: 2024
Издательство: Elsevier BV
Местоположение издательства: Netherlands
Номер статьи: 107400
DOI: 10.1016/j.precamres.2024.107400
Аннотация: The long-lived (billions of years) 40K, 235U, 238U, and 232Th isotopes have a high energy capacity and represent a potent internal source of energy. Together with the external action of the Sun, the natural radioactivity was apparently an important component of evolution of the early Earth and development of Earth’s life. The decay of isotopes initiated radiation chemical reactions involving water, which were accompanied by the formation of hydrogen and oxygen and the transformation of Earth’s inorganic matter into organic compounds, including prebiotic molecules. Water radiolysis in the Earth’s crust continuously produces H2, which is now considered as the main electron donor (food) for microorganisms several kilometers below the Earth’s surface. Here we calculate the initial radioactivity of the early Earth’s crust from the relative abundances of elements and dynamics of variation of the radioactivity and energy release upon the decay of particular radioactive isotopes. The energy released upon the decay of heavy 235U, 238U, and 232Th throughout the existence of the Earth (4.6 billion years) was 4.5 × 1030 J, while the energy released upon the decay of 40K was approximately 1.0 × 1030 J. The energy release per year during the first billion years decreased from 3.0 × 1021 J to 1.5 × 1021 J for heavy isotopes and from 0.70 × 1021 J to 0.45 × 1021 J for 40K. Over the last billion years, the energy decreased approximately threefold. Analysis of the data on the radiation chemical formation of hydrogen in the wet components of the Earth’s crust (cements, zeolites, geopolymers, and other) and bottom sediments indicates that hydrogen is formed upon direct action of radiation on water in yields characteristic of pure water. According to calculations, over the past 4 billion years, approximately 1.7 × 1022 M of hydrogen was formed. Furthermore, ~93 % of H2 was due to the decay of uranium and thorium, while the contribution of 40K did not exceed 7 %. The global rate of hydrogen formation in the Earth’s crust is ~ 1.5 × 1012 mol per year. A mechanism involving ionic and radical products of water radiolysis was proposed to describe the formation of prebiotic molecules (amino acids, sugars, etc.) from carbon-, nitrogen-, and sulfur-containing inorganic compounds.
Добавил в систему: Ершов Борис Григорьевич

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Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earthстатья