Special Issue "Early Earth Environments and Biospheric Evolution"

A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Biogeosciences".

Deadline for manuscript submissions: closed (30 September 2018)

Special Issue Editor

Guest Editor
Dr. Christophe Thomazo

MCF Géochimie, Université de Bourgogne, France
Website | E-Mail
Interests: biogeochemical cycles; mineral-microorganisms interactions; early life on Earth environment; isotopic biosignatures; isotopes geochemistry

Special Issue Information

Dear Colleagues,

In the last few decades, the field of Geobiology, which aims at deciphering the interactions between the physical Earth and biosphere, largely developed and many exciting breakthroughs have been made in our understanding of the co-evolution of life and Earth-driving mechanisms.

This Special Issue of Geosciences invites contributions on latest insights from the Precambrian rock records and modern analogues to decipher interactions between early life and Earth systems.

Studies based on biogeochemical proxies, such as, but not limited to, C, N, S and Fe isotopes, specific compound biomarkers, as well as fossil morphology (microfossils, biomats), batch culture experiments and fossilization experiments, which can improve our understanding of biosignatures of Precambrian metabolisms and their temporal evolution in interactions with Earth surficial reservoirs (i.e., atmosphere, oceans and continental land masses) are encouraged. We also welcome contributions using micro- to nano-scale analyses looking for biogenicity of earliest life traces and discussing the nature of their host environments. Additionally, geochemical box models and numerical approaches applied to Precambrian surficial geobiological co-evolution are welcomed.

It is recommended that authors approach the Guest Editor at an early stage before submission in order to confirm the appropriateness of their potential contributions.

Dr. Christophe Thomazo
Guest Editor

Manuscript Submission Information

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Keywords

  • Early Life
  • Precambrian
  • Geobiology
  • Geochemistry
  • Earth system
  • Microfossils
  • Biomarkers
  • Stable isotopes
  • Great oxygenation event
  • Cyanobacteria

Published Papers (2 papers)

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Research

Open AccessArticle Plant Tissue Decay in Long-Term Experiments with Microbial Mats
Geosciences 2018, 8(11), 387; https://doi.org/10.3390/geosciences8110387
Received: 30 August 2018 / Revised: 17 October 2018 / Accepted: 19 October 2018 / Published: 25 October 2018
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Abstract
The sequence of decay in fern pinnules was tracked using the species Davallia canariensis. Taphonomic alterations in the sediment–water interface (control tanks) and in subaqueous conditions with microbial mats were compared. The decay sequences were similar in control and mat tanks; in [...] Read more.
The sequence of decay in fern pinnules was tracked using the species Davallia canariensis. Taphonomic alterations in the sediment–water interface (control tanks) and in subaqueous conditions with microbial mats were compared. The decay sequences were similar in control and mat tanks; in both cases, pinnules preserved the shape throughout the four-month experience. However, the quality and integrity of tissues were greater in mats. In control tanks, in which we detected anoxic and neutral acid conditions, the appearance of a fungal–bacterial biofilm promoted mechanical (cell breakage and tissue distortions) and geochemical changes (infrequent mineralizations) on the external and internal pinnule tissues. In mats, characterized by stable dissolved oxygen and basic pH, pinnules became progressively entombed. These settings, together with the products derived from mat metabolisms (exopolymeric substances, proteins, and rich-Ca nucleation), promoted the integrity of external and internal tissues, and favored massive and diverse mineralization processes. The experience validates that the patterns of taphonomic alterations may be applied in fossil plants. Full article
(This article belongs to the Special Issue Early Earth Environments and Biospheric Evolution)
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Open AccessArticle Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions
Geosciences 2018, 8(8), 298; https://doi.org/10.3390/geosciences8080298
Received: 1 July 2018 / Revised: 17 July 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
Cited by 2 | PDF Full-text (1027 KB) | HTML Full-text | XML Full-text
Abstract
One of the prior current astrobiological tasks is revealing the limits of microbial resistance to extraterrestrial conditions. Much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the Earth. The aim of this research was [...] Read more.
One of the prior current astrobiological tasks is revealing the limits of microbial resistance to extraterrestrial conditions. Much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the Earth. The aim of this research was to study the impact of accelerated electrons (~1 MeV) as component of space radiation on microbial communities in their natural habitat—the arid soil and ancient permafrost, and also on the pure bacterial cultures that were isolated from these ecotopes. The irradiation was carried out at low pressure (~0.01 Torr) and low temperature (−130 °C) to simulate the conditions of Mars or outer space. High doses of 10 kGy and 100 kGy were used to assess the effect of dose accumulation in inactive and hypometabolic cells, depending on environmental conditions under long-term irradiation estimated on a geological time scale. It was shown that irradiation with accelerated electrons in the applied doses did not sterilize native samples from Earth extreme habitats. The data obtained suggests that viable Earth-like microorganisms can be preserved in the anabiotic state for at least 1.3 and 20 million years in the regolith of modern Mars in the shallow subsurface layer and at a 5 m depth, respectively. In addition, the results of the study indicate the possibility of maintaining terrestrial like life in the ice of Europa at a 10 cm depth for at least ~170 years or for at least 400 thousand years in open space within meteorites. It is established that bacteria in natural habitat has a much higher resistance to in situ irradiation with accelerated electrons when compared to their stability in pure isolated cultures. Thanks to the protective properties of the heterophase environment and the interaction between microbial populations even radiosensitive microorganisms as members of the native microbial communities are able to withstand very high doses of ionizing radiation. Full article
(This article belongs to the Special Issue Early Earth Environments and Biospheric Evolution)
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