Carbon in the Core: Its Influence on the Properties of Core and Mantle

Wood, Bernard J.; Li, Jie; Shahar, Anat

doi:10.2138/rmg.2013.75.8

Cited by 120 publications

(116 citation statements)

References 92 publications

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“…It is not precisely known how much of which elements the core contains besides Fe and Ni, but the most likely suspects are C, S, O, and Si, because they are common and abundant elements in the Sun and in planets and are known to form alloys with Fe at high pressure and temperature. 83 A conservative estimate is that the Fe-Ni alloy in the core contains about 0.2% by weight carbon. Because the mass of the core is 2 × 10 12 Gt, it therefore contains about 4 billion GtC, which constitutes about 90% of the Earth's carbon (and 1 million Figure 5.…”

Section: The Natural Carbon Cycle(s)mentioning

confidence: 99%

Sustainable carbon emissions: The geologic perspective

DePaolo

2015

MRS Energy & Sustainability

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Discussion of climate change usually focuses on the rise of Earth's global average surface temperature. Because of the variability in temperature-daily, weekly, seasonal, annual, decadal-and the seemingly small temperature rise 15 (about 1 °C) recorded so far, global surface temperature increase is diffi cult to appreciate for many people. 61 The more dramatic effects of warming-melting glaciers and sea ice-are happening in high latitude regions where few people live. The observed temperature increase is itself misleading; although seemingly modest, it is an underestimate of the effect, because the temperature will continue to rise based on the current greenhouse gas content of the atmosphere and the projected continued emissions. The temperature rise to date is only a fraction of that already programmed into the Earth system. 15 , 59 The root cause of climate change is what could be called "carbon cycle change." To change climate, the amount of carbon dioxide and other so-called greenhouse gases in the atmosphere needs to change. 7 , 61 , 67 , 71 To change the amount of CO 2 in the atmosphere, there must be a change in the way carbon is transferred among the various forms and places it exists in and on the Earth. The movement of carbon between storage "reservoirs" on the Earth, including the atmosphere, is complicated and still under investigation. 15 , 34 , 77 This study is an attempt to present a simplifi ed version of the carbon cycle, to place the current discussions of climate change in a geological perspective and provide an entry point for those wishing to ABSTRACT Current issues with carbon emissions need to be understood in terms of natural geologic processes that move carbon on the Earth. Comparison of modern emissions with the norms and extremes of natural processes emphasizes the enormity of the current challenge, and also the reason there are uncertainties about the future effects. Reaching sustainable emissions in the future can be viewed as a need to systematically reduce the carbon intensity of energy production.Achieving sustainable carbon emissions requires understanding of Earth's natural carbon cycles. Geologic processes move carbon in large quantities between Earth reservoirs, including in and out of the deeper reaches of the planet, and regulate Earth's surface temperature within a narrow range suitable for life for the past 3-4 billion years. There have been large changes in atmospheric CO 2 in the geologic past; the largest to offset changes in the brightness of the Sun. Atmospheric CO 2 has been much higher in the past, but not since humans evolved. Geologic processes act slowly, even during times in the geologic past regarded as examples of catastrophic climate change. In contrast, over the past 100 years, Earth's carbon cycles have undergone revolutionary change as a result of a greatly accelerated transfer of carbon from geologic storage to the atmosphere . Today, about 98% of the movement of carbon out of geologic reservoirs (coal-, oil-, and gas-bearing sedimentary rocks and l...

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Section: The Natural Carbon Cycle(s)mentioning

confidence: 99%

Sustainable carbon emissions: The geologic perspective

DePaolo

2015

MRS Energy & Sustainability

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“…The first one is the single stage model or equilibrium model, in which chemical equilibrium between the core and the mantle is thought to be achieved at certain P-T conditions at the base of the magma ocean (Li and Agee, 1996;Righter, 2011 The second endmember mode is the continuous core formation model (Wood et al, 2006(Wood et al, , 2013. In this model, Earth accretion and the delivery of coreforming metal occur in small steps of 1 % mass with constant metal/silicate ratio.…”

Section: Resultsmentioning

confidence: 99%

“…In each step the metal equilibrates with the silicate magma ocean, and it remains chemically isolated once it segregates in the core. The fractionation of light element isotopes in this model can best be described by the Rayleigh distillation model (Wood et al, 2013;Horita and Polyakov, 2015) (Fig. 3).…”

Section: Resultsmentioning

confidence: 99%

Nitrogen isotope fractionation during terrestrial core-mantle separation

Li¹,

Marty²,

Shcheka³

et al. 2016

Geochem. Persp. Let.

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doi: 10.7185/geochemlet.1614The origin and evolution of the terrestrial nitrogen remains largely unresolved. In order to understand the potential influence of core-mantle separation on terrestrial nitrogen evolution, experiments were performed at 1.5 to 7.0 GPa and 1600 to 1800 °C to study nitrogen isotope fractionation between coexisting liquid Fe-rich metal and silicate melt. The results show that the metal/silicate partition coefficient of nitrogen D N metal/silicate ranges from 1 to 150 and the nitrogen isotope fractionation d15 N metal-silicate is −3.5 ± 1.7 ‰. Calculations show that the bulk Earth is more depleted in d 15 N than the present-day mantle, and that the presentday mantle d 15 N of −5 ‰ could be derived from an enstatite chondrite composition via terrestrial core-mantle separation, with or without the addition of carbonaceous chondrites. These results strongly support the notion that enstatite chondrites may be a main component from which the Earth formed and a main source of the terrestrial nitrogen. Moreover, in the deep reduced mantle, the Fe-rich metal phase may store most of the nitrogen, and partial melting of the coexisting silicates may generate oceanic island basalts (OIBs) with slightly positive d15 N values.

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“…During the differentiation into core and mantle, this carbon could partly be dissolved in the core material, leaving a mantle depleted in carbon. This is derived from recent studies that found that the outer core of Earth may contain some carbon at the 1% weight level (Nakajima et al 2015;Wood et al 2013). 6.…”

Section: Carbon Content Of Planetesimalsmentioning

confidence: 99%

Spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals

Gail

Trieloff

2017

A&A

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Context. A high fraction of carbon bound in solid carbonaceous material is observed to exist in bodies formed in the cold outskirts of the solar nebula, while bodies in the region of terrestrial planets contain only very small mass fractions of carbon. Most of the solid carbon component is lost and converted into CO during the spiral-in of matter as the Sun accretes matter from the solar nebula. Aims. We study the fate of the carbonaceous material that entered the proto-solar disc by comparing the initial carbon abundance in primitive solar system material and the abundance of residual carbon in planetesimals and planets in the asteroid belt and the terrestrial planet region. Methods. We constructed a model for the composition of the pristine carbonaceous material from observational data on the composition of the dust component in comets and of interplanetary dust particles and from published data on pyrolysis experiments. This material entered the inner parts of the solar nebula during the course of the build-up of the proto-sun by accreting matter from the proto-stellar disc. Based on a one-zone evolution model of the solar nebula, we studied the pyrolysis of the refractory and volatile organic component and the concomitant release of hydrocarbons of high molecular weight under quiescent conditions of disc evolution, while matter migrates into the central parts of the solar nebula. We also studied the decomposition and oxidation of the carbonaceous material during violent flash heating events, which are thought to be responsible for the formation of chondrules. To do this, we calculated pyrolysis and oxidation of the carbonaceous material in temperature spikes that were modeled according to cosmochemical models for the temperature history of chondrules. Results. We find that the complex hydrocarbon components of the carbonaceous material are removed from the disc matter in the temperature range between 250 and 400 K, but the amorphous carbon component survives to temperatures of 1200 K. Without efficient carbon destruction during flash-heating associated with chondrule formation, the carbon abundance of terrestrial planets, except for Mercury, would be of several percent and not as low as it is found in cosmochemical studies. Chondrule formation seems to be a crucial process for the carbon-poor composition of the material of terrestrial planets.

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Carbon in the Core: Its Influence on the Properties of Core and Mantle

Cited by 120 publications

References 92 publications

Sustainable carbon emissions: The geologic perspective

Sustainable carbon emissions: The geologic perspective

Nitrogen isotope fractionation during terrestrial core-mantle separation

Spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals

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