ID 57034
Author
Ota, Tsutomu Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University
Aihara, Yuhei Department of Earth and Planetary Sciences, Kyushu University
Kiyokawa, Shoichi Department of Earth and Planetary Sciences, Kyushu University
Tanaka, Ryoji Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University
Nakamura, Eizo Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Planetary Materials, Okayama University
Abstract
The RNA World hypothesis requires the synthesis of RNA to allow the emergence of life on Earth. Hydrothermal systems have been proposed as potential candidates for constructing complex biomolecules. However, in order to successfully form RNA, it is necessary to stabilize ribose, a RNA carbohydrate component. Borate has been found to stabilize ribose. Therefore, boron rich hydrothermal systems are important environments concerning the origin of life on Earth.
The 3.2-Ga Dixon Island Formation of the West Pilbara Superterrane, Western Australia, is a volcano-sedimentary sequence. The Formation represents a Mesoarchean pelagic hydrothermal system, which formed adjacent to an immature island arc. Fine-grained tourmaline, in addition to biogenic carbonaceous matter and spherulitic and tubular bacteriomorphs, are found in black chert. A boron-rich environment was responsible for the formation of these deposits. To explore the implications of such a boron enriched environment on microbial activity, modes of occurrence and chemical compositions of the tourmaline were examined.
The tourmaline is schorl or dravite of the alkali tourmaline group and the boron isotope compositions range in δ11B from -7.3 to +2.6‰. The tourmaline occurs in microcrystalline quartz matrix of black chert veins that cross cut a volcanic unit and also in a bedded black chert, which overlays the volcanic unit. The volcanic unit contains highly altered zones with hydrothermal veins. The associated lithologic and stratigraphic features suggest that the black chert veins were the conduits for upward moving hydrothermal fluids, which reached the sea floor. Subsequently, the volcanic unit was covered by organic matter-rich cherty sediments that in part were fed, and/or altered, by the hydrothermal fluids.
These results suggest that the origin of boron enrichment to form Dixon Island tourmaline is not the associated sedimentary mineral assemblage, which includes diagenetic clay, low-grade metamorphic mica, and organic matter. Instead, the tourmaline was directly precipitated from hydrothermal fluid, enriched in boron. Furthermore, the hydrothermal fluids had already concentrated the boron, in the Mesoarchean pelagic system, prior to the apex of organic matter production and microbial activity. Our findings support a hypothesis that the boron-enriched hydrothermal environment aided the survival and evolution of early life.
Keywords
Mesoarchean
Hydrothermal system
Early life
Boron
Tourmaline
Note
This fulltext will be available in Nov 2021
Published Date
2019-11
Publication Title
Precambrian Research
Volume
volume334
Publisher
Elsevier
Start Page
105475
ISSN
03019268
NCID
AA00780095
Content Type
Journal Article
language
英語
OAI-PMH Set
岡山大学
File Version
author
DOI
Related Url
isVersionOf https://doi.org/10.1016/j.precamres.2019.105475