Venus’ light slab hinders its development of planetary-scale subduction and habitability

Abstract Terrestrial planets Venus and Earth have similar sizes, masses, and bulk compositions, but only Earth developed planetary-scale plate tectonics. Plate tectonics generates weatherable fresh rocks and transfers surface carbon back to Earth’s interior, which provides a long-term climate feedback, serving as a thermostat to keep Earth a habitable planet. Yet Venus shares a few common features with early Earth, such as stagnant-lid tectonics and the possible early development of a liquid ocean. Given all these similarities with early Earth, why would Venus fail to develop global-scale plate tectonics? In this study, we explore solutions to this problem by examining Venus’ slab densities under hypothesized subduction-zone conditions. Our petrologic simulations show that eclogite facies may be reached at greater depths on Venus than on Earth, and Venus’ slab densities are consistently lower than Earth’s. We suggest that the lack of sufficient density contrast between the high-pressure metamorphosed slab and mantle rocks may have impeded self-sustaining subduction. Although plume-induced crustal downwelling exists on Venus, the dipping of Venus’ crustal rocks to mantle depth fails to transition into subduction tectonics. As a consequence, the supply of fresh silicate rocks to the surface has been limited. This missing carbon sink eventually diverged the evolution of Venus’ surface environment from that of Earth.

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The long-term climate evolution and planetary habitability – Onset timing of the plate tectonics in early Earth

10.5194/egusphere-egu2020-9209 ◽

2020 ◽

Author(s):

Takashi Nakagawa

Keyword(s):

Plate Tectonics ◽

Planetary System ◽

Early Earth ◽

Volcanic Degassing ◽

Deep Mantle ◽

Onset Timing ◽

Climate Evolution ◽

Plate Subduction ◽

Volatile Cycling

The plate tectonics is an essential geophysical/geological process on the deep mantle water and carbon cycling, which may also control the long-term climate evolution because the volcanic degassing induced by the plate subduction seems to change the atmospheric condition. However, as suggested by the geological evidence on the onset timing of the plate tectonics in early Earth, which is modeled by the transition from the stagnant lid tectonics to the plate subduction, this timing may have great uncertainty. Here, two questions are addressed: 1. How can the deep mantle volatile cycling would be affected by the onset timing of the plate tectonics in the planetary system evolution?; 2. As a result of the successful scenario of the deep mantle volatile cycling explained for the observational constraints of the subduction flux of the water and carbon, how can the climate evolution be responded as a function of the history of the deep mantle volatile cycling such as the subduction flux? To address these questions, a simplified model of whole planetary system evolution based on the thermal history computation of the silicate mantle coupled with the energy balance climate evolution and deep mantle volatile is used with controlling both heat transfer and volatile cycling associated with the transition between stagnant lid and plate tectonics.&#160;The main result indicates that plate tectonics may be essential for the mild and stable climate that allows having liquid water over billions of years of the time scale. This is because a sufficient amount of volcanic degassing can be found for the vigorous plate tectonics rather than the stagnant lid state to get the long-term mild climate. For the stagnant lid state, the snowball limit cycle can be found. Thus, the vigorous plate motion may contribute to stabilizing the warm climate.&#160;To find out the constraint on the present-day surface environment, the transition timing from the stagnant lid to the vigorous plate subduction for explaining the present-day amount of volatiles and their subduction flux would range from 1 to 3 Ga. And, around 5 to 10 ocean masses of the water in the total planetary system is required so that the deep mantle melting should be continuously found to supply the volatile component to the atmosphere associated with the plate subduction, which is worked for the reducing the melting temperature of the silicate mantle. However, the subduction flux for finding the mild climate is one to two orders of magnitude larger than the expected from the geological constraint &#8211; 1012 to 1013 kg/yr as well as some difficulty for explaining the global sea-level change. In the presentation, some improvements on including the big storage capacity of the volatiles in the mantle transition zone will be provided for giving a better understanding of both the deep mantle volatile cycle and climate evolution in the plate-mantle evolution system.

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A CO2 greenhouse efficiently warmed the early Earth and decreased seawater 18O/16O before the onset of plate tectonics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2023617118 ◽

2021 ◽

Vol 118 (23) ◽

pp. e2023617118

Author(s):

Daniel Herwartz ◽

Andreas Pack ◽

Thorsten J. Nagel

Keyword(s):

Plate Tectonics ◽

Isotope Composition ◽

Oxygen Isotopic Composition ◽

Early Earth ◽

Time Interval ◽

Hot Climate ◽

Oxygen Isotopic ◽

Low Degrees ◽

Chemical Sediments

The low 18O/16O stable isotope ratios (δ18O) of ancient chemical sediments imply ∼70 °C Archean oceans if the oxygen isotopic composition of seawater (sw) was similar to modern values. Models suggesting lower δ18Osw of Archean seawater due to intense continental weathering and/or low degrees of hydrothermal alteration are inconsistent with the triple oxygen isotope composition (Δ’17O) of Precambrian cherts. We show that high CO2 sequestration fluxes into the oceanic crust, associated with extensive silicification, lowered the δ18Osw of seawater on the early Earth without affecting the Δ’17O. Hence, the controversial long-term trend of increasing δ18O in chemical sediments over Earth’s history partly reflects increasing δ18Osw due to decreasing atmospheric pCO2. We suggest that δ18Osw increased from about −5‰ at 3.2 Ga to a new steady-state value close to −2‰ at 2.6 Ga, coinciding with a profound drop in pCO2 that has been suggested for this time interval. Using the moderately low δ18Osw values, a warm but not hot climate can be inferred from the δ18O of the most pristine chemical sediments. Our results are most consistent with a model in which the “faint young Sun” was efficiently counterbalanced by a high-pCO2 greenhouse atmosphere before 3 Ga.

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Pedogenic processes and the drying of Mars

10.31223/x5ng9j ◽

2021 ◽

Author(s):

Adrian Broz ◽

Lucas Silva

Keyword(s):

Liquid Water ◽

Plate Tectonics ◽

Soil Formation ◽

Global Scale ◽

Recycle Water ◽

Definition Of ◽

Pedogenic Processes ◽

Biological Component ◽

Critical Process

New insights from Mars suggest crustal hydration contributed to the long-term drying of the planet. Three to four billion years ago, hydration of the Martian crust could have resulted from precipitation-driven surface weathering of mafic sediments, which on Earth leads to pedogenesis, i.e., the formation of soil. Although soil has been traditionally defined by its biological component, growing evidence of global scale soil formation on a presumably lifeless Mars suggests abiotic pedogenesis was a critical process early in the planet’s history. Using a recently updated definition of soil as leverage, we argue that pedogenic processes could have consumed large amounts of Mars’ exchangeable liquid water. Since there is no evidence of plate tectonics to liberate and recycle water from hydrated pedogenic minerals on Mars, the global formation of soil billions of years ago could have contributed to the irreversible desiccation of the planet.

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Modelling long-term blanket peatland development in eastern Scotland

10.5194/bg-2019-230 ◽

2019 ◽

Author(s):

Ward Swinnen ◽

Nils Broothaerts ◽

Gert Verstraeten

Keyword(s):

Dynamic Equilibrium ◽

Carbon Sink ◽

Regional Climate ◽

Global Scale ◽

Growth Potential ◽

Peat Bogs ◽

Peatland Development ◽

Spatially Distributed ◽

Blanket Peatlands

Abstract. Blanket peatlands constitute a rare ecosystem on a global scale but is the most important peatland type on the British Isles. Most long-term peatland development models have focussed on peat bogs and high-latitude regions. Here, we present a spatially-explicit hillslope model to simulate long-term blanket peatland development along complex hillslope topographies. To calibrate the model, the peatland architecture was reconstructed along 56 hillslope transects in the headwaters of the river Dee (633 km2) in eastern Scotland, resulting in a dataset of 866 soil profile descriptions. The application of the calibrated model using local pollen-based land cover and regional climate reconstructions over the last 12,000 years shows that the early-Holocene peatland development is largely driven by a temperature increase. An increase in woodland cover only has a slight positive effect on the peat growth potential contradicting the hypothesis that blanket peatland developed as a response to deforestation. Both the hillslope measurements and the model simulations demonstrate that the blanket peatland cover in the study area is highly variable both in extent and peat thickness stressing the need for spatially distributed peatland modelling. At the landscape scale, blanket peatlands were an important atmospheric carbon sink during the period 9.5 ka–6 ka BP. However, during the last six thousand years, the blanket peatlands are in a state of dynamic equilibrium with minor changes in the carbon balance.

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The142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2006950117 ◽

2020 ◽

Vol 117 (26) ◽

pp. 14738-14744 ◽

Cited By ~ 1

Author(s):

Eugenia Hyung ◽

Stein B. Jacobsen

Keyword(s):

Plate Tectonics ◽

Early Earth ◽

Solar System Formation ◽

Crustal Rocks ◽

Stirring Rate ◽

Mid Ocean Ridge ◽

Stirring Time ◽

Ocean Ridge ◽

Island Basalt ◽

4.1 Ga

Early silicate differentiation events for the terrestrial planets can be traced with the short-lived146Sm-142Nd system (∼100-My half-life). Resulting early Earth-produced142Nd/144Nd variations are an excellent tracer of the rate of mantle mixing and thus a potential tracer of plate tectonics through time. Evidence for early silicate differentiation in the Hadean (4.6 to 4.0 Ga) has been provided by142Nd/144Nd measurements of rocks that show both higher and lower (±20 ppm) values than the present-day mantle, demonstrating major silicate Earth differentiation within the first 100 My of solar system formation. We have obtained an external 2σ uncertainty at 1.7 ppm for142Nd/144Nd measurements to constrain its homogeneity/heterogeneity in the mantle for the last 2 Ga. We report that most modern-day mid-ocean ridge basalt and ocean island basalt samples as well as continental crustal rocks going back to 2 Ga are within 1.7 ppm of the average Earth142Nd/144Nd value. Considering mafic and ultramafic compositions, we use a mantle-mixing model to show that this trend is consistent with a mantle stirring time of about 400 My since the early Hadean. Such a fast mantle stirring rate supports the notion that Earth’s thermal and chemical evolution is likely to have been largely regulated by plate tectonics for most of its history. Some young rocks have142Nd/144Nd signatures marginally resolved (∼3 ppm), suggesting that the entire mantle is not equally well homogenized and that some silicate mantle signatures from an early differentiated mantle (>4.1 Ga ago) are preserved in the modern mantle.

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Chilling Out

10.1093/oso/9780198717867.003.0010 ◽

2018 ◽

Author(s):

Roy Livermore

Keyword(s):

Plate Tectonics ◽

Volcanic Eruptions ◽

Atmospheric Temperature ◽

Ocean Currents ◽

Mountain Ranges ◽

Continental Rifts ◽

Earth’S Climate ◽

The One ◽

Tectonic Forces

The Earth’s climate changes naturally on all timescales. At the short end of the spectrum—hours or days—it is affected by sudden events such as volcanic eruptions, which raise the atmospheric temperature directly, and also indirectly, by the addition of greenhouse gases such as water vapour and carbon dioxide. Over years, centuries, and millennia, climate is influenced by changes in ocean currents that, ultimately, are controlled by the geography of ocean basins. On scales of thousands to hundreds of thousands of years, the Earth’s orbit around the Sun is the crucial influence, producing glaciations and interglacials, such as the one in which we live. Longer still, tectonic forces operate over millions of years to produce mountain ranges like the Himalayas and continental rifts such as that in East Africa, which profoundly affect atmospheric circulation, creating deserts and monsoons. Over tens to hundreds of millions of years, plate movements gradually rearrange the continents, creating new oceans and destroying old ones, making and breaking land and sea connections, assembling and disassembling supercontinents, resulting in fundamental changes in heat transport by ocean currents. Finally, over the very long term—billions of years—climate reflects slow changes in solar luminosity as the planet heads towards a fiery Armageddon. All but two of these controls are direct or indirect consequences of plate tectonics.

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A systemic socio-ecological recovery from Covid-19

Global Social Policy ◽

10.1177/14680181211019166 ◽

2021 ◽

pp. 146801812110191

Author(s):

William Hynes

Keyword(s):

Financial Economic ◽

Global Scale ◽

Economic Approach ◽

Short Term ◽

Current Crisis ◽

Policy Alternatives ◽

Economic Thinking ◽

Emergency Measures ◽

Ecological Recovery

New economic thinking and acting through a systemic approach could outline policy alternatives to tackle the global-scale systemic challenges of financial, economic, social and environmental emergencies, and help steer our recovery out of the current crisis. A systemic recovery requires an economic approach that balances several factors - markets and states, efficiency and resilience, growth and sustainability, national and global stability, short-term emergency measures and long-term structural change. To achieve this, we need to think beyond our policy silos, comprehend our interconnections, and build resilience into our systems.

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Innovatory role of nanomaterials as bio-tools for treatment of cancer

Reviews in Inorganic Chemistry ◽

10.1515/revic-2020-0015 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Khuram Shahzad Ahmad ◽

Muntaha Talat ◽

Shaan Bibi Jaffri ◽

Neelofer Shaheen

Keyword(s):

Cancer Treatment ◽

Cancer Therapeutics ◽

Physicochemical Characteristics ◽

Global Scale ◽

Current Review ◽

Anti Cancer ◽

Different Types ◽

Cancerous Cells

AbstractConventional treatment modes like chemotherapy, thermal and radiations aimed at cancerous cells eradication are marked by destruction pointing the employment of nanomaterials as sustainable and auspicious materials for saving human lives. Cancer has been deemed as the second leading cause of death on a global scale. Nanomaterials employment in cancer treatment is based on the utilization of their inherent physicochemical characteristics in addition to their modification for using as nano-carriers and nano-vehicles eluted with anti-cancer drugs. Current work has reviewed the significant role of different types of nanomaterials in cancer therapeutics and diagnostics in a systematic way. Compilation of review has been done by analyzing voluminous investigations employing ERIC, MEDLINE, NHS Evidence and Web of Science databases. Search engines used were Google scholar, Jstore and PubMed. Current review is suggestive of the remarkable performance of nanomaterials making them candidates for cancer treatment for substitution of destructive treatment modes through investigation of their physicochemical characteristics, utilization outputs and long term impacts in patients.

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Shared socioeconomic pathways for climate change research in Finland: co-developing extended SSP narratives for agriculture

Regional Environmental Change ◽

10.1007/s10113-020-01734-2 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Heikki S. Lehtonen ◽

Jyrki Aakkula ◽

Stefan Fronzek ◽

Janne Helin ◽

Mikael Hildén ◽

...

Keyword(s):

Climate Change ◽

National Level ◽

Global Scale ◽

Change Scenario ◽

Policy Makers ◽

Climate Change Research ◽

Food And Agriculture ◽

Agriculture And Food ◽

Farm Subsidies

AbstractShared socioeconomic pathways (SSPs), developed at global scale, comprise narrative descriptions and quantifications of future world developments that are intended for climate change scenario analysis. However, their extension to national and regional scales can be challenging. Here, we present SSP narratives co-developed with stakeholders for the agriculture and food sector in Finland. These are derived from intensive discussions at a workshop attended by approximately 39 participants offering a range of sectoral perspectives. Using general background descriptions of the SSPs for Europe, facilitated discussions were held in parallel for each of four SSPs reflecting very different contexts for the development of the sector up to 2050 and beyond. Discussions focused on five themes from the perspectives of consumers, producers and policy-makers, included a joint final session and allowed for post-workshop feedback. Results reflect careful sector-based, national-level interpretations of the global SSPs from which we have constructed consensus narratives. Our results also show important critical remarks and minority viewpoints. Interesting features of the Finnish narratives compared to the global SSP narratives include greater emphasis on environmental quality; significant land abandonment in SSPs with reduced livestock production and increased plant-based diets; continued need for some farm subsidies across all SSPs and opportunities for diversifying domestic production under scenarios of restricted trade. Our results can contribute to the development of more detailed national long-term scenarios for food and agriculture that are both relevant for local stakeholders and researchers as well as being consistent with global scenarios being applied internationally.

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Broken Worlds: Towards an Archaeology of the Shatter Zone

Journal of Archaeological Method and Theory ◽

10.1007/s10816-021-09520-y ◽

2021 ◽

Author(s):

Ben Raffield

Keyword(s):

Eighteenth Century ◽

Global Scale ◽

Physical Geography ◽

Trigger Factors ◽

Eastern Woodlands ◽

Term Change ◽

Anthropological Research ◽

Historic Change

AbstractIn recent years, archaeological studies of long-term change and transformation in the human past have often been dominated by the discussion of dichotomous processes of ‘collapse’ and ‘resilience’. These discussions are frequently framed in relatively narrow terms dictated by specialist interests that place an emphasis on the role of single ‘trigger’ factors as motors for historic change. In order to address this issue, in this article I propose that the study of the ‘shatter zone’—a term with origins in physical geography and geopolitics that has been more recently harnessed in anthropological research—has the potential to facilitate multi-scalar, interdisciplinary analyses of the ways in which major historical changes unfold across both space and time, at local, regional, and inter-regional levels. This article unpacks the concept of the shatter zone and aligns this with existing archaeological frameworks for the study of long-term adaptive change. I then situate these arguments within the context of recent studies of colonial interaction and conflict in the Eastern Woodlands of North America during the sixteenth to eighteenth century. The study demonstrates how a more regulated approach to the shatter zone has the potential to yield new insights on the ways in which populations mitigate and react to instability and change while also facilitating comparative studies of these processes on a broader, global scale.

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