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Archean kerogen as a new tracer of atmospheric evolution : Implications for dating the widespread nature of early life

Bekaert, D.V. ; Broadley, M.W. ; Delarue, F. ; Avice, G. ; Robert, F. ; Marty, B., Science Advances

Archean kerogen as a new tracer of atmospheric evolution : Implications for dating the widespread nature of early life

Bekaert, D.V. ; Broadley, M.W. ; Delarue, F. ; Avice, G. ; Robert, F. ; Marty, B.

Science Advances, 2018, 4 :eaar2091

Abstract :

Understanding the composition of the Archean atmosphere is vital for unraveling the origin of volatiles and the environmental conditions that led to the development of life. The isotopic composition of xenon in the Archean atmosphere has evolved through time by mass-dependent fractionation from a precursor comprising cometary and solar/chondritic contributions (referred to as U-Xe). Evaluating the composition of the Archean atmosphere is challenging because limited amounts of atmospheric gas are trappedwithinminerals during their formation.Weshow that organicmatter, known to be efficient at preserving large quantities of noble gases, can be used as a new archive of atmospheric noble gases. Xe isotopes in a kerogen isolated fromthe 3.0–billion year–old FarrelQuartzite (Pilbara Craton, Western Australia) are mass fractionated by 9.8 ± 2.1 per mil (‰) (2s) per atomic mass unit, in line with a progressive evolution toward modern atmospheric values. Archean atmospheric Xe signatures in kerogens open a new avenue for following the evolution of atmospheric composition through time. The degree of mass fractionation of Xe isotopes relative to the modern atmosphere can provide a time stamp for dating Archean kerogens and therefore narrowing the time window for the diversification of early life during the Archean eon.

Voir en ligne : http://dx.doi.org/DOI:10.1126/sciad...




publié lundi 19 mars 2018