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Evidencia de camas masivas de siderita para una atmósfera rica en CO2 antes de hace aproximadamente 1.800 millones de
Hiroshi Ohmoto1, Yumiko Watanabe, Kazumasa Kumazawa
1Astrobiology Research Center of the NASA Astrobiology Institute and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA. ohmoto@geosc.psu.edu
Nature
|May 28, 2004
Resumen
Tierra temprana de la Tierra temprana.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Paleoclimatología Paleoclimatología
- Los estudios de la Tierra temprana estudian la Tierra.
Sus antecedentes:
- La Tierra temprana probablemente requirió gases de efecto invernadero para mantener los océanos líquidos debido al menor flujo solar.
- El metano ha sido hipotetizado como un gas de efecto invernadero clave antes de hace 2.2 mil millones de años.
- Esta hipótesis se basó en la ausencia de siderita en los paleosols, lo que sugiere un bajo nivel de dióxido de carbono atmosférico.
Objetivo del estudio:
- Reevaluar el papel del metano y el dióxido de carbono en el mantenimiento de los primeros océanos líquidos de la Tierra.
- Para investigar las restricciones geológicas sobre la composición atmosférica.
Principales métodos:
- Análisis termodinámicos multidimensionales.
- Examen de la evidencia geológica, específicamente los paleosolos y los lechos ricos en siderita.
- Análisis de las proporciones de isótopos de carbono en secuencias sedimentarias.
Principales resultados:
- La ausencia de siderita en los paleosols no restringe de manera confiable los niveles de dióxido de carbono atmosférico.
- La formación de siderita depende del oxígeno y el pH del suelo, favoreciendo los minerales férricos en suelos bien aireados.
- La siderita se ha formado constantemente en el subsuelo, en ambientes anaeróbicos a lo largo de la historia geológica.
- Los abundantes lechos de siderita en secuencias anteriores a 1.800 millones de años indican un dióxido de carbono atmosférico significativamente más alto (>100 veces los niveles actuales).
Conclusiones:
- El dióxido de carbono solo, sin metano significativo, podría haber proporcionado un efecto invernadero suficiente para los océanos líquidos de la Tierra temprana.
- Los niveles de CO2 atmosférico de la Tierra primitiva eran sustancialmente más altos de lo que se había deducido previamente de la ausencia de siderita en los paleosolos.
- Las altas concentraciones de CO2 probablemente llevaron a más lluvia ácida y aguas oceánicas en la Tierra temprana.
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