Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record

A morphogram for silica-witherite biomorphs and its application to microfossil identification in the early earth rock record

Geobiology ◽

10.1111/gbi.12278 ◽

2018 ◽

Vol 16 (3) ◽

pp. 279-296 ◽

Cited By ~ 24

Author(s):

J. Rouillard ◽

J.-M. García-Ruiz ◽

J. Gong ◽

M. A. van Zuilen

Keyword(s):

Early Earth ◽

Rock Record

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Organic biomorphs may be better preserved than microorganisms in early Earth sediments

Geology ◽

10.1130/g48152.1 ◽

2021 ◽

Author(s):

Christine Nims ◽

Julia Lafond ◽

Julien Alleon ◽

Alexis S. Templeton ◽

Julie Cosmidis

Keyword(s):

Early Life ◽

Colloidal Silica ◽

Early Earth ◽

Correct Identification ◽

Precambrian Rock ◽

Geochemical Conditions ◽

Organic Composition ◽

Siliceous Rocks ◽

Rock Record ◽

Life On Earth

The Precambrian rock record contains numerous examples of microscopic organic filaments and spheres, commonly interpreted as fossil microorganisms. Microfossils are among the oldest traces of life on Earth, making their correct identification crucial to our understanding of early evolution. Yet, spherical and filamentous microscopic objects composed of organic carbon and sulfur can form in the abiogenic reaction of sulfide with organic compounds. Termed organic biomorphs, these objects form under geochemical conditions relevant to the sulfidic environments of early Earth. Furthermore, they adopt a diversity of morphologies that closely mimic a number of microfossil examples from the Precambrian record. Here, we tested the potential for organic biomorphs to be preserved in cherts; i.e., siliceous rocks hosting abundant microbial fossils. We performed experimental silicification of the biomorphs along with the sulfur bacterium Thiothrix. We show that the original morphologies of the biomorphs are well preserved through encrustation by nano-colloidal silica, while the shapes of Thiothrix cells degrade. Sulfur diffuses from the interior of both biomorphs and Thiothrix during silicification, leaving behind empty organic envelopes. Although the organic composition of the biomorphs differs from that of Thiothrix cells, both types of objects present similar nitrogen/carbon ratios after silicification. During silicification, sulfur accumulates along the organic envelopes of the biomorphs, which may promote sulfurization and preservation through diagenesis. Organic biomorphs possessing morphological and chemical characteristics of microfossils may thus be an important component in Precambrian cherts, challenging our understanding of the early life record.

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Experimental fossilisation of viruses from extremophilic Archaea

Biogeosciences ◽

10.5194/bg-8-1465-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 1465-1475 ◽

Cited By ~ 19

Author(s):

F. Orange ◽

A. Chabin ◽

A. Gorlas ◽

S. Lucas-Staat ◽

C. Geslin ◽

...

Keyword(s):

Origin Of Life ◽

Extreme Environments ◽

Early Earth ◽

Sulfolobus Islandicus ◽

Viral Particles ◽

Rock Record ◽

Extremophilic Microorganisms ◽

The Origin Of Life ◽

Pyrococcus Abyssi

Abstract. The role of viruses at different stages of the origin of life has recently been reconsidered. It appears that viruses may have accompanied the earliest forms of life, allowing the transition from an RNA to a DNA world and possibly being involved in the shaping of tree of life in the three domains that we know presently. In addition, a large variety of viruses has been recently identified in extreme environments, hosted by extremophilic microorganisms, in ecosystems considered as analogues to those of the early Earth. Traces of life on the early Earth were preserved by the precipitation of silica on the organic structures. We present the results of the first experimental fossilisation by silica of viruses from extremophilic Archaea (SIRV2 – Sulfolobus islandicus rod-shaped virus 2, TPV1 – Thermococcus prieurii virus 1, and PAV1 – Pyrococcus abyssi virus 1). Our results confirm that viruses can be fossilised, with silica precipitating on the different viral structures (proteins, envelope) over several months in a manner similar to that of other experimentally and naturally fossilised microorganisms. This study thus suggests that viral remains or traces could be preserved in the rock record although their identification may be challenging due to the small size of the viral particles.

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