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Reevaluar la primera aparición de los eucariotas y las cianobacterias
Birger Rasmussen1, Ian R Fletcher, Jochen J Brocks
1Department of Applied Geology, Curtin University of Technology, Kent Street, Bentley, Western Australia 6102, Australia. B.Rasmussen@curtin.edu.au
Nature
|October 25, 2008
Resumen
Un nuevo análisis de las antiguas pizarras de esquisto australianas desafía la evidencia temprana de la fotosíntesis oxigenada. Los biomarcadores que anteriormente se pensaba que indicaban cianobacterias y eucariotas hace 2.700 millones de años ahora se consideran contaminantes, rechazando las primeras evidencias fósiles.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- La paleobiología es la paleobiología.
- Geología Geología Geología.
Sus antecedentes:
- La fotosíntesis oxigenada alteró profundamente la química de la Tierra, lo que llevó al aumento del oxígeno atmosférico y a las edades de hielo.
- La evidencia previa para la fotosíntesis oxigenada temprana (hace 2.7 Gyr) se basó en biomarcadores en esquisto australiano, lo que sugiere eucariotas y cianobacterias.
Objetivo del estudio:
- Reevaluar el origen indígena de los biomarcadores en las pizarras de esquisto australianas de 2,7 años de antigüedad.
- Determinar la edad real de los primeros eucariotas y cianobacterias basándose en pruebas fósiles fiables.
Principales métodos:
- Medidas in situ del isótopo de carbono (13C/12C) del pirobitumo y el querógeno a escala micrométrica.
- Análisis de las pizarras metamorfoseadas del Cratón Pilbara, Australia, incluidas muestras que anteriormente producían biomarcadores.
Principales resultados:
- El querógeno y el pirobitumen indígenas están significativamente agotados en 13C, lo que indica que son isotópicamente más ligeros que los hidrocarburos previamente extraídos.
- Las proporciones de 13C/12C son inconsistentes con un origen indígena para los biomarcadores encontrados en las pizarras.
- Los biomarcadores se introdujeron después del metamorfismo (aprox. 2.2 Gyr hace), invalidando su uso como evidencia de la vida arcaica.
Conclusiones:
- La evidencia fósil más antigua para los eucariotas es ahora 1.781.68 Gyr hace, y para las cianobacterias es de aproximadamente. Hace 2.15 años.
- El estudio elimina la evidencia de la fotosíntesis oxigenada hace 2.7 Gyr.
- Esto revisa nuestra comprensión de la línea de tiempo entre la aparición de las cianobacterias y el aumento del oxígeno atmosférico.
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