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Posts Tagged ‘August 2019’

v15n4 People in the News

Professor Donald Bruce Dingwell, Director of the Department of Earth and Environmental Sciences at the University of Munich (Germany), has been awarded the Volcanology and Igneous Petrology (VIP) Career Achievement Award from the Geological Association of Canada (GAC) for his lifelong contributions to volcanology and igneous petrology.

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Book Review — Clays in the Critical Zone

The Earth’s oldest rocks are those which formed in the time interval 3.0–4.0 billion years ago in the mid- to early Archaean Eon. Traces of anything even earlier, which would be from the Hadean (>4.0 billion years ago), are fragmental and preserved only in detrital zircon grains and in the isotopic memory of now long-extinct isotope systems. The time interval 3.0–4.0 billion years ago is a crucial stage in Earth history, for this is when the first continents formed, when life began, and was a time during which tectonic processes were quite different from modern (Phanerozoic) plate tectonics due to the different thermal state of the young Earth.

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The Apollo Sample Collection: 50 Years Of Solar System Insight

The Apollo program was the seminal moment in modern human history and the crowning technological achievement of the 20th century. In addition to the obvious historical, cultural, and technological significance of the Apollo program, scientific results from the Apollo lunar samples have had a lasting impact on a range of scientific fields, none more so than on the fields of planetary science and cosmochemistry. Over the past five decades, studies of these lunar samples have yielded significant insights into planetary bodies throughout the solar system. Despite the Apollo samples being a static collection, recent and ongoing studies continue to make new significant discoveries. Here, we will discuss the collection, curation, and study of the Apollo lunar samples and look forward to some expected new developments in the coming years.

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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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Palaeoweathering: How Do Weathering Rates Vary with Climate?

A feedback between Earth surface weathering and climate is thought to be fundamental in maintaining Earth’s habitability over long timescales, but investigating this control in the modern world is difficult. The geologic record of cycles between glacial and interglacial conditions of the last 2.6 million years allows us to study weathering feedback in action. A suite of mineral, element and isotope proxies have been applied to address how weathering rates have varied over glacial cycles. Despite evidence for substantial local changes, the emerging answer at a global scale seems to be, “not very much”.

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Combating Climate Change Through Enhanced Weathering of Agricultural Soils

Rising levels of atmospheric carbon dioxide (CO2) are driving increases in global temperatures. Enhanced weathering of silicate rocks is a CO2 removal technology that could help mitigate anthropogenic climate change. Enhanced weathering adds powdered silicate rock to agricultural lands, accelerating natural chemical weathering, and is expected to rapidly draw down atmospheric CO2. However, differences between enhanced and natural weathering result in significant uncertainties about its potential efficacy. This article summarizes the research into enhanced weathering and the uncertainties of enhanced weathering due to the key differences with natural weathering, as well as future research directions.

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Breaking it Down: Mechanical Processes in the Weathering Engine

Since land plants emerged from swampy coastlines over 400 million years ago, they have played a fundamental role in shaping the Earth system. Roots and associated fungi increase rock weathering rates, providing access to nutrients, while altering atmospheric CO2. As soils weather, the dissolution of primary minerals forces plants to rely on recycling and atmospheric deposition of rock-derived nutrients. Thus, for many terrestrial ecosystems, weathering ultimately constrains primary production (carbon uptake) and decomposition (carbon loss). These constraints are most acute in agricultural systems, which rely on mined fertilizer rather than the recycling of organic material to maintain production. Humans now mine similar amounts of some elements as weather out of rocks globally. This increase in supply has myriad environmental consequences.

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How Plants Enhance Weathering and How Weathering is Important to Plants

Since land plants emerged from swampy coastlines over 400 million years ago, they have played a fundamental role in shaping the Earth system. Roots and associated fungi increase rock weathering rates, providing access to nutrients, while altering atmospheric CO2. As soils weather, the dissolution of primary minerals forces plants to rely on recycling and atmospheric deposition of rock-derived nutrients. Thus, for many terrestrial ecosystems, weathering ultimately constrains primary production (carbon uptake) and decomposition (carbon loss). These constraints are most acute in agricultural systems, which rely on mined fertilizer rather than the recycling of organic material to maintain production. Humans now mine similar amounts of some elements as weather out of rocks globally. This increase in supply has myriad environmental consequences.

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The Goldilocks Planet? How Silicate Weathering Maintains Earth “Just Right”

Earth’s climate is buffered over long timescales by a negative feedback between atmospheric CO2 level and surface temperature. The rate of silicate weathering slows as the climate cools, causing CO2 to increase and warming the surface through the greenhouse effect. This buffering system has kept liquid water stable at Earth’s surface, except perhaps during certain ‘Snowball Earth’ episodes at the beginning and end of the Proterozoic. A similar stabilizing feedback is predicted to occur on rocky planets orbiting other stars if they share analogous properties with Earth, most importantly an adequate (but not overly large) abundance of water and a mechanism for recycling carbonate rocks into CO2. Periodic oscillations between globally glaciated and ice-free climates may occur on planets with weak stellar insolation and/or slow volcanic outgassing rates. Most silicate weathering is thought to occur on the continents today, but seafloor weathering (and reverse weathering) may have been equally important earlier in Earth’s history.

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