Preservation and Distributions of Covalently Bound Polyaromatic Hydrocarbons in Ancient Biogenic Kerogens and Insoluble Organic Macromolecules

The likelihood of finding pristine molecular biosignatures preserved in Earth's oldest rocks or on other planetary bodies is low, and new approaches are needed to assess the origins of highly altered and recalcitrant organic matter. In this study, we aim to understand the distributions and systematics of preservation of ancient polycyclic aromatic hydrocarbons (PAHs), as both free hydrocarbons and bound within insoluble macromolecules. We report the distributions of bound PAHs generated by catalytic hydropyrolysis from ancient biogenic kerogens and from insoluble organic matter (IOM) in high-temperature carbonaceous residues from pyrobitumens and synthetic coke. For biogenic kerogens, the degree of thermal maturity exerts the primary control on the preservation and distributions of the major five-ring and six-ring PAH compounds. This holds for both Precambrian and Phanerozoic rocks, thus source variation in primary biogenic organic matter inputs does not exert the major control on bound PAH. The IOM samples, predominantly residues from hydrocarbon cracking at high temperatures, preserve a bound PAH profile significantly distinct from ancient biogenic kerogens and characterized by an absence of perylene and higher abundance of large-ring condensed PAHs. Covalently bound PAH profiles offer promise as "last resort" molecular biosignatures for aiding the astrobiological search for ancient life.

Ediacara biota flourished in oligotrophic and bacterially dominated marine environments across Baltica

Middle-to-late Ediacaran (575–541 Ma) marine sedimentary rocks record the first appearance of macroscopic, multicellular body fossils, yet little is known about the environments and food sources that sustained this enigmatic fauna. Here, we perform a lipid biomarker and stable isotope (δ¹⁵N_total and δ¹³C_TOC) investigation of exceptionally immature late Ediacaran strata (<560 Ma) from multiple locations across Baltica. Our results show that the biomarker assemblages encompass an exceptionally wide range of hopane/sterane ratios (1.6–119), which is a broad measure of bacterial/eukaryotic source organism inputs. These include some unusually high hopane/sterane ratios (22–119), particularly during the peak in diversity and abundance of the Ediacara biota. A high contribution of bacteria to the overall low productivity may have bolstered a microbial loop, locally sustaining dissolved organic matter as an important organic nutrient. These oligotrophic, shallow-marine conditions extended over hundreds of kilometers across Baltica and persisted for more than 10 million years.

The environments and food sources that sustained Ediacara biota 575-541 million years ago remain unclear. Here, the authors perform lipid biomarker and isotopic analyses on biota fossil-containing Ediacaran strata from Baltica and propose the presence of a microbial loop bolstered by bacteria.

Why don't we use vitamin E in dermatology?

OBJECTIVE

To review the possible uses of topical and systemic tocopherols as therapy for skin conditions in light of the widespread use of vitamin E by patients.

DATA SOURCES

Index Medicus was searched for articles published from 1922 (when vitamin E was discovered) to 1966 (the beginning of MEDLINE). MEDLINE was searched for articles in English and French on vitamin E or tocopherol in relation to dermatology. Additional original articles were identified from the reference lists of the review articles.

STUDY SELECTION

Only well-designed controlled studies were accepted; anecdotes and open studies are cited for completeness and as direction for future research.

DATA SYNTHESIS

There was some weak or conflicting evidence that vitamin E is of value in yellow nail syndrome, vibration disease, epidermolysis bullosa, cancer prevention, claudication, cutaneous ulcers, and collagen synthesis and wound healing. It was of no use in atopic dermatitis, dermatitis herpetiformis, psoriasis, subcorneal pustular dermatosis, porphyrias and skin damage induced by ultraviolet light.

CONCLUSIONS

After 44 years of research there is still scant proof of vitamin E's effectiveness in treating certain dermatologic conditions. Further research in well-designed controlled trials is needed to clarify vitamin E's role.

Cutis marmorata telangiectatica congenita: long-term follow-up, review of the literature, and report of a case in conjunction with congenital hypothyroidism

Cutis marmorata telangiectatica congenita is an uncommon, generally congenital, cutaneous condition. The major skin findings are persistent, fixed cutis marmorata, telangiectasia, and phlebectasia; often, there is associated skin atrophy and ulceration as well. Significantly, two-thirds of patients have other congenital anomalies, although often minor ones. We report a series of eight children with cutis marmorata telangiectatica congenita, including one with associated congenital hypothyroidism, a relationship that has never before been noted.

Dermatology in a war zone: a Persian Gulf experience

The clinical experience of two US Army dermatologists during the recent Gulf War (Operation Desert Shield/Storm) are presented with comparison with dermatologic experience in previous wars and in civilian practice.