Thematic Articles

Virtual Archaeology of Altered Paintings: Multiscale Chemical Imaging Tools

By , , and | February, 2016

Understanding how painted works of art were constructed, layer-by-layer, requires a range of macroscopic and microscopic X-ray and infrared-based analytical methods. Deconstructing complex assemblies of paints horizontally across a picture and vertically through it provides insight into the detailed production process of the art work and on the painting techniques and styles of its maker. The unwanted chemical transformations that some paint pigments undergo are also detectable; these changes can alter the paint’s optical properties. Understanding the chemistry behind such paint degradation gives conservators vital clues to counter these effects and is an invaluable asset in protecting these cultural artifacts for future generations.

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The Earth Sciences from the Perspective of an Art Museum

By , and | February, 2016

The scientific investigation of works of art has an essential role in understanding museum collections and is fundamental in establishing successful conservation and restoration strategies. In the multidisciplinary environment of museums, scientists work with conservators and curators not only to more profoundly understand works of art but to better preserve them, and this often involves using analytical techniques borrowed from different disciplines of Earth sciences (e.g. mineralogy, geochemistry, and petrology). Two case studies – the stones of Angkor (Cambodia) and a blue paint mineral pigment – demonstrate how the Earth sciences are helping to identify, determine provenance, and conserve a broad spectrum of works of art. The impact on archaeological and art historical scholarship is substantial.

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Geochronology Beyond Radiocarbon: Optically Stimulated Luminescence Dating of Palaenvironments and Archaeological Sites

By and | February, 2016

This article reviews optically stimulated luminescence (OSL) dating as used on Quaternary sediments and for archaeological dating. The underlying physics is summarized and the laboratory method itself is described. Examples of OSL dating illustrate its use in palaeoenvironmental and archaeological contexts, although problems associated with the technique are also addressed. Finally, we discuss long-range variants of OSL that may help date deposits currently considered too old for OSL to be applied.

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Application of Geophysical Methods to Cultural Heritage

By , and | February, 2016

Archaeological geophysics is a vital part of exploring and documenting cultural heritage. Three of the most commonly used techniques are magnetometry, resistivity, and ground penetrating radar. These methods help archaeological geophysicists to unravel the complexity of many archaeological sites, including urban ones, old buildings, and built structures of cultural importance. However, local factors, such as constraints on time, local environment, pre-existing available information, and budgets, all contribute to a given site requiring unique geophysical surveying strategies. Four Spanish-based, but generally applicable, case studies will illustrate key geophysical strategy types for particular local archaeological conditions.

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The Contribution of Geoscience to Cultural Heritage Studies

By and | February, 2016

This issue of Elements celebrates the diverse contributions that the Earth sciences have made to characterizing, interpreting, conserving, and valorizing cultural heritage. Archaeometry and conservation science are connected to the geosciences at different levels. Earth scientists possess a profound perception of the complexity of natural materials, they have the necessary knowledge of the ancient and recent geological and physico-chemical processes acting on natural materials and on the artifacts produced by human activities, and they master most of the techniques useful to investigate our common heritage. Therefore, Earth scientists can greatly contribute towards a better understanding and preservation of our past.

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Emerging Frontiers in Geomicrobiology

By and | December, 2015

The interdisciplinary field of geomicrobiology and microbial geochemistry (GMG) has provided surprising insights into microbial function and preservation in diverse environments. The emerging frontiers in GMG are driven by recent discoveries in material sciences, economic geology, human health, and paleontology. The length-scales and mechanisms by which organisms can transfer electrons are being redefined, which have implications ranging from the formation of ore deposits to microbial function in the human body. Pathways of biomineralization are a critical control for many fossilization processes. Microbiologically produced materials also exhibit great potential for technological and medical applications.

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Emerging Biogeochemical Views of Earth’s Ancient Microbial Worlds

By , and | December, 2015

Microbial processes dominate geochemical cycles at and near the Earth’s surface today. Their role was even greater in the past, with microbes being the dominant life form for the first 90% of Earth’s history. Most of their metabolic pathways originated billions of years ago as both causes and effects of environmental changes of the highest order, such as the first accumulation of oxygen in the oceans and atmosphere. Microbial processes leave behind diverse geochemical fingerprints that can remain intact for billions of years. These rock-bound signatures are now steering our understanding of how life coevolved with the environments on early Earth and are guiding our search for life elsewhere in the universe.

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Cryptic Cross-Linkages Among Biogeochemical Cycles: Novel Insights from Reactive Intermediates

By , and | December, 2015

The biogeochemical cycling of major and minor elements in the ocean has direct bearing on the health of the planet and its inhabitants. Reactive intermediates, of both chemical and biological origin, are emerging as important players in these biogeochemical cycles. Due to their rapid production and consumption, these reactive intermediates are short-lived and typically in low concentration. Involvement of these “invisible” species in biogeochemistry may therefore be hidden, or cryptic, with no obvious lingering chemical signature. Here, we highlight reactive intermediates of the oxygen, manganese, and sulfur cycles and how these intermediates are involved in cryptic cross-linkages between marine biogeochemical cycles of global importance.

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Omic Approaches to Microbial Geochemistry

By and | December, 2015

The past two decades have witnessed an explosion of DNA sequencing technologies that provide unprecedented insights into genome sequences­—the blueprints of life on Earth. Although initially driven by biomedical research, this revolution offers exciting opportunities in Earth sciences. Analyzing genomes and other biomolecules (“omic” methods) within environmental samples provides new vistas of microbial geochemistry. However, the massive amount of data produced can be hard to decipher, and the resources and infrastructure to train and support geoscientists in omics approaches are lacking. This article summarizes some of the opportunities and challenges in the applications of omic approaches to geochemical problems.

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Principles of Geobiochemistry

By and | December, 2015

The basic premise of geobiochemistry is that life emerged on Earth where there were opportunities for catalysis to expedite the release of chemical energy in water–rock–organic systems. In this framework, life is a planetary response to the dilemma that cooling decreases the rates of abiotic processes to the point that chemical energy becomes trapped. Catalysis via metabolism releases the trapped energy, and life benefits by capturing some of the energy released. Out of necessity, biochemical processes have geochemical origins, and geobiochemistry asserts that these origins can be revealed by mapping reaction mechanisms onto deep time. We propose five principles that should help guide research in the emerging field of geobiochemistry.

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Geomicrobiology and Microbial Geochemistry

By and | December, 2015

Geomicrobiology and microbial geochemistry (GMG) investigates the interaction between Earth, environmental systems, and microbial life. Microbes shape their geochemical surroundings through their metabolic and growth needs and thereby exert significant geochemical and mineralogical control on their local environments. In turn, local geochemical conditions dictate what metabolic processes are possible. These mutual influences mean that microbial evolution has occurred in concert with changing geosphere conditions and that microbes have driven major shifts in ocean, continent and atmospheric chemistry. If one wishes to understand element cycling in any system containing water, one must realize that microbes are critical to the story.

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