Carbon — Beautiful, Essential, Deadly

The unique physical chemistry of carbon confers an extraordinary ability to form molecules that are variously beautiful (think diamond), essential (think living cells), and toxic (think greenhouse gas). Nowhere is this split personality more evident than in the enigmatic igneous clan of kimberlites, the topic for this issue of Elements. No one who has set eyes on a cut diamond, especially the delicate pink stones from soon-to-close Argyle Mine in Western Australia (see photo to the right), can fail to be awestruck at Nature’s capacity for beauty. Kimberlite magmas that bring diamonds to the surface are carbon-fuelled, whether by methane through a complex series of redox melting reactions (see Foley et al. 2019 this issue p. 393), or by carbon dioxide exsolving from kimberlite melt at sub-crustal depths and propelling it explosively to the surface (see Russell et al. 2019 this issue p. 405). We have yet to witness a kimberlite erupt – the last known eruption, in Tanzania, was ten thousand years ago – but we can be fairly sure that the greenhouse gas delivery of a single kimberlite pipe in full flow was pretty substantial. For kimberlites, carbon is both passenger and propellant.

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Celebration of the Periodic Table

The periodic table of chemical elements is one of the most significant achievements in science because it arranges the 118 known elements in a deceptively simple pattern that reveals their properties. So how did this “Rosetta Stone of Nature” originate?

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Weathering: Earth’s Inexorable Millstone

Mere centuries from now, almost every physical object you’ve bought or wrought will have disappeared from the face of the Earth. Nature’s forces will conspire to erase your archeological record. Unless you live in a stone manor, the foundations of your home will gradually crumble due to carbonic acid seeping into hairline cracks. Soil will migrate and turn over, shifting and consuming whatever objets d’art now grace your yard. Oxidation and sunlight will yellow and crack exposed plastic and paper. And everywhere, always, a teeming horde of plant roots, invertebrates, moles, and their microbial friends and relations will disaggregate and eat whatever they can. In the blink of a geological eye, almost your entire archaeological record will very likely be buried, broken down, and swept away.

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Hail Hephaestus, Interdisciplinary Deity!

The Aegean region of the Eastern Mediterranean can claim, with good reason, to be a cradle of modern civilisation and scholarship. As we learn in this issue of Elements, the Aegean is also home to some extraordinary geology, including Santorini Volcano whose Late Bronze Age eruption presaged (but did not actually cause, we learn on p. 185) the demise of the mighty Minoan dynasty on Crete. The so-called Minoan eruption was one of many eruptions from Aegean volcanoes that took place under the watchful eye of the Ancient Greek gods, not least Hephaestus, god of fire and son of Zeus.

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Does Earth Still Offer Discoveries?

Imagine a geoscientist who begins his career as a mine surveyor but who quickly realizes that this was too small a field for him. So, he decides to take field trips, which last many years, to remote parts of the Earth. What our geoscientist discovers includes nothing less than the interactions between topography and climate, the alignment of volcanoes along zones of earthquake activity and at great depth, and three-quarters of all known plant species. Returning home, our geoscientist does not rest. Instead, he lets the world know of his spectacular discoveries. He becomes a prolific writer who publishes an immense number of articles and books, all the while discussing the implications of his findings in a dozen or more detailed letters a day with colleagues around the world.

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Mineralogical Revelations From Space Odysseys

Sir Arthur C. Clarke (1917–2008), perhaps best known for the 1968 book and film 2001: A Space Odyssey, once stated that “The only way of discovering the limits of the possible is to venture a little way past them into the impossible.” As you enjoy this issue of Elements on planet Mercury, think about the remarkable achievement of sending a spacecraft to Mercury, the closest planet to the Sun.

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The Irony of Iron — Life’s Major Trace Element

All organisms, from lowly microbes to higher forms of life (including humans), need iron. Yet there is irony to iron. Despite being the second most abundant element in the Earth, it is not readily available for consumption. Earth owes this irony to the combined effects of geodynamics and biology. The early segregation of iron into the Earth’s core relegated iron to “only” the fourth most abundant element in the crust. About 2.3 billion years ago, a complex interplay between photosynthesis and redox changes in Earth’s mantle allowed the buildup of free atmospheric oxygen. Today, there is a sufficient supply of photosynthetic oxygen to convert all iron at the Earth’s surface and in its surface waters, including seawater, into its ferric [Fe(III)] form. This ferric form is barely soluble, making it hard to access by organisms. Ironically, life itself made iron a ‘trace element’.

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The “Plasticene” Epoch?

This issue of Elements explores the fascinating realm of deep-ocean deposits that have the potential to provide society with many of the raw mineral resources required to meet the world’s growing needs. While raw materials have always, and always will, play a critical role in meeting these demands, materials made by humans have also become increasingly important, expanding in concert along with the world’s population, industry, and resource use. Most notably, plastics, which are synthetic organic polymers derived from fossil hydrocarbons, have become an indispensable part of our material world because of their remarkable number of uses and versatility. Plastic bottles, bags, credit cards, scotch tape, pipes, toys, to name a few, form part of our everyday life. Not surprisingly, the global production of plastic has increased from 2 metric tons (Mt) in 1950 to 380 Mt in 2015 (Geyer et al. 2017). By 2050, Geyer et al. (2017) estimate that roughly 12,000 Mt of plastic waste will be in the natural environment. This is a staggering amount, enough to cover the entire surface of the Earth in a thin layer of plastic! With the growing abundance of plastic, the potential for preservation in the rock record increases. What impact will synthetic materials like plastic have on future deposits in the Earth – will there be a “Plasticene Epoch”?

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Ethically Sourced Metals

The Central Andes is a land of llamas, salt flats and majestic volcanic peaks. It is one of most remote places on Earth and arguably the driest. In a not unconnected way, the Central Andes is also home to the world’s largest copper mines. The unique combination of magmas, tectonics and climate, described in this issue of Elements, has conspired to create hydrothermal ore deposits that provide a third of the world’s copper and a quarter of its molybdenum.

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The Making of Great Wine

As we set up the publication schedule for each year, the principal editors of Elements try to ensure that the journal maintains enough diversity to hold the interest of you, our readers. In this context, we sometimes accept proposals for issues on very well-known mainstream subjects (such as layered intrusions) which we think can usefully be updated and summarised at a good level. We also try, however, to bring you subjects which are outside the mainstream yet still can be grouped loosely within the areas of geochemistry, mineralogy and petrology. That is how we categorise the current issue dealing with the environmental aspects of making high-quality wine.

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