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La evidencia de isótopos de azufre para una atmósfera arqueana óxica

Hiroshi Ohmoto¹, Yumiko Watanabe, Hiroaki Ikemi

¹NASA Astrobiology Institute and Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. ohmoto@geosc.psu.edu

|August 25, 2006

Resumen

Los isótopos de azufre independientes de la masa (MIF-S) están ausentes en las antiguas rocas australianas, lo que desafía la idea de una atmósfera oxigenada temprana. Este hallazgo sugiere que los orígenes de MIF-S pueden no depender únicamente de la química atmosférica.

Área de la Ciencia:

La geoquímica es la geoquímica.
Geología de Isótopos Geología de Isótopos.
Las paleoatmósferas.

Sus antecedentes:

Se pensó que la fraccionamiento independiente de masa de isótopos de azufre (MIF-S) en rocas de más de 2.400 millones de años indicaba una atmósfera anóxica.
La ausencia de MIF-S en rocas más jóvenes apoyó una transición a una atmósfera óxica, atribuida a la fotólisis UV del dióxido de azufre.

Objetivo del estudio:

Para investigar la presencia y el origen de MIF-S en antiguas rocas sedimentarias.
Reevaluar el vínculo entre MIF-S y los niveles de oxígeno atmosférico durante la era Arqueana.

Principales métodos:

Análisis de isótopos de azufre en secciones de aproximadamente 100 m de sedimentos lacustres de 2,76-Gyr.
Análisis de isótopos de azufre en pizarras marinas de 2,92 años de antigüedad del Cratón Pilbara, Australia Occidental.

Principales resultados:

Se detectó la ausencia de MIF-S tanto en los antiguos sedimentos lacustres como en las pizarras marinas.
Este hallazgo contrasta con la presencia esperada de MIF-S en rocas de esta edad basada en modelos anteriores.

Conclusiones:

El registro geológico de MIF-S puede requerir reinterpretación.
Las posibles explicaciones incluyen la fluctuación de los niveles de oxígeno de Archaean, la actividad volcánica que influye en MIF-S, o procesos diagenéticos no fotoquímicos que crean MIF-S independientemente de la química atmosférica.

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