How to Detect Organic Life From the Hadean

Possible Biosphere-Lithosphere Interactions Preserved in Igneous Zircon and Implications for Hadean Earth

Authors:

Dustin et al

Abstract:

Granitoids are silicic rocks that make up the majority of the continental crust, but different models arise for the origins of these rocks. One classification scheme defines different granitoid types on the basis of materials involved in the melting/crystallization process. In this end-member case, granitoids may be derived from melting of a preexisting igneous rock, while other granitoids, by contrast, are formed or influenced by melting of buried sedimentary material. In the latter case, assimilated sedimentary material altered by chemical processes occurring at the near surface of Earth—including biological activity—could influence magma chemical properties. Here, we apply a redox-sensitive calibration based on the incorporation of Ce into zircon crystals found in these two rock types, termed sedimentary-type (S-type) and igneous-type (I-type) granitoids. The ∼400 Ma Lachlan Fold Belt rocks of southeastern Australia were chosen for investigation here; these rocks have been a key target used to describe and explore granitoid genesis for close to 50 years. We observe that zircons found in S-type granitoids formed under more reducing conditions than those formed from I-type granitoids from the same terrain. This observation, while reflecting 9 granitoids and 289 analyses of zircons from a region where over 400 different plutons have been identified, is consistent with the incorporation of (reduced) organic matter in the former and highlights one possible manner in which life may modify the composition of igneous minerals. The chemical properties of rocks or igneous minerals may extend the search for ancient biological activity to the earliest period of known igneous activity, which dates back to ∼4.4 billion years ago. If organic matter was incorporated into Hadean sediments that were buried and melted, then these biological remnants could imprint a chemical signature within the subsequent melt and the resulting crystal assemblage, including zircon.

Molecular Fossils Found From the Early Cambrian, China

Molecular fossils extracted from the Early Cambrian section in the Three Gorges area, South China

Authors:

Yamada et al

Abstract:

Environmental investigation of the Early Cambrian is assessed through molecular fossils based from three core samples drilled in the Three Gorges area, South China. The core samples record environmental information dating from the earliest part of the Early Cambrian to nearly the end of the Early Cambrian, making this investigation unique from previous investigations because a more far-reaching temporal record is assessed. This record includes unusually high abundance of longer chain n-alkanes (LCA) around nC27, having been recognized in the earliest Cambrian strata. Based on no odd–even preference of the LCA and comparisons to hydrocarbons in cultured cells of microorganisms, the LCA may be derived from hydrocarbons of sulfate reducing bacteria. On the other hand, a phototrophic origin of the SCA is supported by a clear positive correlation with pristane. The relative abundance of LCA to SCA increased in the earliest Cambrian, suggesting predominance of sulfate reducers against phototrophs. This LCA abundance with simultaneous decrease of pristane/phytane may indicate a euxinic condition, where sulfate reducers remineralize organic carbon in the water column. This is consistent with the concomitant decrease of the δ13Ccarb value probably due to a massive reoxidation of organic carbon. The inferred reducing condition is further supported by the enhanced appearance of squalane that could be derived from an Archeal lipid. Our results suggest the euxinia of the Yangtze platform in the earliest Cambrian that may relate to the emergence of the large nektonic animals which require sufficient level of free oxygen.

Frasnian Devonian Fossil Yields 70 Different Steroids, Setting Record for Oldest Organic Molecular Fossils Found

Curtin University PhD candidate Ines Melendez says the lipids are 380 million years old, or about 250 million years older than what had been the oldest known find of its kind.

"This is the first detailed molecular study … on a carbonate concretion from the Devonian Reef," she says.

Her supervisor, Professor Kliti Grice, says the fossil was originally a crustacean that died in the oceans around the time of the Devonian mass-extinctions (more than 360 million years ago).

It fed on smaller organisms in the oxygenated upper layer of water, and when it died it sank into a lower layer of anoxic water.

"Sulfate reducers degrade that organic matter anerobically, yielding hydrogen sulfide utilised in photosynthesis by organisms called Chlorobi at the interface between the oxygenated and anoxic layers," Prof Grice says.

Ms Melendez says these microbes then formed a community around the dead crustacean.

"There was so much organic matter that they didn't degrade everything," she says.

"The conditions helped these organisms to start to precipitate carbonate—whatever was left was encapsulated inside and wasn't used any more.

"In that way the concretion kept growing."

She analysed the fossil, finding molecules of 70 different steroids.

link.

Studying Precambrian Proteins

Modern proteins exhibit an impressive degree of structural diversity, which has been well characterized, but very little is known about how and when over the course of evolution 3D protein structures arose.

In a study published by Cell Press August 8 in Structure, researchers resurrected 4-billion-year-old Precambrian proteins in the laboratory and gained novel insights into protein evolution by analyzing their X-ray crystal structures. This method has revealed a remarkable degree of structural similarity among proteins since life first evolved on this planet, and it represents a powerful and novel approach to explore the evolution of protein structures.

"So far, attempts to understand protein structure evolution have been based on the comparison between structures of modern proteins. This is equivalent to trying to understand the evolution of birds by comparing several living birds," says senior study author Jose Sanchez-Ruiz of the University of Granada. "But it is most useful to study fossils so that changes over evolutionary time are apparent. Our approach comes as close as possible to 'digging up' fossil protein structures."

In a recent study, Sanchez-Ruiz and his collaborators constructed a phylogenetic tree of protein sequences by analyzing the amino acid sequences of thioredoxins—proteins found in organisms from the three domains of life, including bacteria, archaea and eukaryotes. Using this phylogenetic tree, they were able to resurrect Precambrian proteins in the laboratory and characterize their features.

Early Cambrian Molecular Fossils Recovered

Molecular fossils extracted from the Early Cambrian section in the Three Gorges area, South China

Authors:

1. Kentaro Yamada (a)
2. Yuichiro Ueno (a, b)
3. Keita Yamada (c)
4. Tsuyoshi Komiya (d)
5. Jian Han (e)
6. Degan Shu (e)
7. Naohiro Yoshida (b, c)
8. Shigenori Maruyama (a, b)

Affiliations:

a. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

b. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

c. Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta Midori-ku Yokohama, 226-8502, Japan

d. Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan

e. Department of Geology and Key Laboratory for Continental Dynamics, Northwest University, Xi’an 710069, China

Abstract:

Environmental investigation of the Early Cambrian is assessed through molecular fossils based from three core samples drilled in the Three Gorges area, South China. The core samples record environmental information dating from the earliest part of the Early Cambrian to nearly the end of the Early Cambrian, making this investigation unique from previous investigations because a more far-reaching temporal record is assessed. This record includes unusually high abundance of longer chain n-alkanes (LCA) around nC27, having been recognized in the earliest Cambrian strata. Based on no odd-even preference of the LCA and comparisons to hydrocarbons in cultured cells of microorganisms, the LCA may be derived from hydrocarbons of sulfate reducing bacteria. On the other hand, a phototrophic origin of the SCA is supported by a clear positive correlation with pristane. The relative abundance of LCA to SCA increased in the earliest Cambrian, suggesting predominance of sulfate reducers against phototrophs. This LCA abundance with simultaneous decrease of pristane/phytane may indicate a euxinic condition, where sulfate reducers reminreralize organic carbon in the water column. This is consistent with the concomitant decrease of the δ13Ccarb value probably due to a massive reoxidation of organic carbon. The inferred reducing condition is further supported by the enhanced appearance of squalane that could be derived from an Archaeal lipid. Our results suggest the euxinia of the Yantze platform in the earliest Cambrian that may relate to the emergence of the large nektonic animals which require sufficient level of free oxygen.