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Höning D, Spohn T. Land Fraction Diversity on Earth-like Planets and Implications for Their Habitability. ASTROBIOLOGY 2023; 23:372-394. [PMID: 36848252 DOI: 10.1089/ast.2022.0070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
A balanced ratio of ocean to land is believed to be essential for an Earth-like biosphere, and one may conjecture that plate-tectonics planets should be similar in geological properties. After all, the volume of continental crust evolves toward an equilibrium between production and erosion. If the interior thermal states of Earth-sized exoplanets are similar to those of Earth-a straightforward assumption due to the temperature dependence of mantle viscosity-one might expect a similar equilibrium between continental production and erosion to establish, and hence a similar land fraction. We show that this conjecture is not likely to be true. Positive feedback associated with the coupled mantle water-continental crust cycle may rather lead to a manifold of three possible planets, depending on their early history: a land planet, an ocean planet, and a balanced Earth-like planet. In addition, thermal blanketing of the interior by the continents enhances the sensitivity of continental growth to its history and, eventually, to initial conditions. Much of the blanketing effect is, however, compensated by mantle depletion in radioactive elements. A model of the long-term carbonate-silicate cycle shows the land and the ocean planets to differ by about 5 K in average surface temperature. A larger continental surface fraction results both in higher weathering rates and enhanced outgassing, partly compensating each other. Still, the land planet is expected to have a substantially dryer, colder, and harsher climate possibly with extended cold deserts in comparison with the ocean planet and with the present-day Earth. Using a model of balancing water availability and nutrients from continental crust weathering, we find the bioproductivity and the biomass of both the land and ocean planets to be reduced by a third to half of those of Earth. The biosphere on these planets might not be substantial enough to produce a supply of free oxygen.
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Affiliation(s)
- Dennis Höning
- Potsdam-Institute for Climate Impact Research, Potsdam, Germany
| | - Tilman Spohn
- International Space Science Institute, Bern, Switzerland
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Way MJ, Ostberg C, Foley BJ, Gillmann C, Höning D, Lammer H, O’Rourke J, Persson M, Plesa AC, Salvador A, Scherf M, Weller M. Synergies Between Venus & Exoplanetary Observations: Venus and Its Extrasolar Siblings. SPACE SCIENCE REVIEWS 2023; 219:13. [PMID: 36785654 PMCID: PMC9911515 DOI: 10.1007/s11214-023-00953-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 01/11/2023] [Indexed: 06/18/2023]
Abstract
Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.
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Affiliation(s)
- M. J. Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA
- Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Colby Ostberg
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521 USA
| | - Bradford J. Foley
- Department of Geosciences, Pennsylvania State University, University Park, PA USA
| | - Cedric Gillmann
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005 USA
| | - Dennis Höning
- Potsdam Institute for Climate Impact Research, Potsdam, Germany
- Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
| | - Joseph O’Rourke
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA
| | - Moa Persson
- Institut de Recherche en Astrophysique et Planétologie, Centre National de la Recherche Scientifique, Université Paul Sabatier – Toulouse III, Centre National d’Etudes Spatiales, Toulouse, France
| | | | - Arnaud Salvador
- Department of Astronomy and Planetary Science, Northern Arizona University, Box 6010, Flagstaff, AZ 86011 USA
- Habitability, Atmospheres, and Biosignatures Laboratory, University of Arizona, Tucson, AZ USA
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - Manuel Scherf
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
- Institute for Geodesy, Technical University, Graz, Austria
| | - Matthew Weller
- Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 USA
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Chen J, Jiang H, Tang M, Hao J, Tian M, Chu X. Venus' light slab hinders its development of planetary-scale subduction. Nat Commun 2022; 13:7647. [PMID: 36496413 PMCID: PMC9741584 DOI: 10.1038/s41467-022-35304-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 11/24/2022] [Indexed: 12/13/2022] Open
Abstract
Terrestrial planet Venus has a similar size, mass, and bulk composition to Earth. Previous studies proposed that local plume-induced subduction existed on both early Earth and Venus, and this prototype subduction might initiate plate tectonics on Earth but not on Venus. In this study, we simulate the buoyancy of submerged slabs in a hypothesized 2-D thermo-metamorphic model. We analyze the thermal state of the slab, which is then used for calculating density in response to thermal and phase changes. The buoyancy of slab mantle lithosphere is primarily controlled by the temperatures and the buoyancy of slab crust is dominated by metamorphic phase changes. Difference in the eclogitization process contributes most to the slab buoyancy difference between Earth and Venus, which makes the subducted Venus' slab consistently less dense than Earth's. The greater chemical buoyancy on Venus, acting as a resistance to subduction, may have impeded the transition into self-sustained subduction and led to a different tectonic regime on Venus. This hypothesis may be further tested as more petrological data of Venus become available, which will further help to assess the impact of petro-tectonics on the planet's habitability.
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Affiliation(s)
- Junxing Chen
- grid.17063.330000 0001 2157 2938Department of Earth Science, University of Toronto, Toronto, Ontario M5S 3B1 Canada
| | - Hehe Jiang
- grid.17063.330000 0001 2157 2938Department of Earth Science, University of Toronto, Toronto, Ontario M5S 3B1 Canada ,grid.9227.e0000000119573309State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
| | - Ming Tang
- grid.11135.370000 0001 2256 9319Key Laboratory of Orogenic Belt and Crustal Evolution, MOE; School of Earth and Space Science, Peking University, Beijing, 100871 China
| | - Jihua Hao
- grid.59053.3a0000000121679639Deep Space Exploration Laboratory/CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026 China
| | - Meng Tian
- grid.5734.50000 0001 0726 5157Center for Space and Habitability, Universität Bern, Bern, 3012 Switzerland
| | - Xu Chu
- grid.17063.330000 0001 2157 2938Department of Earth Science, University of Toronto, Toronto, Ontario M5S 3B1 Canada
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Graham RJ, Lichtenberg T, Pierrehumbert RT. CO 2 Ocean Bistability on Terrestrial Exoplanets. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2022; 127:e2022JE007456. [PMID: 36589718 PMCID: PMC9787872 DOI: 10.1029/2022je007456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 09/26/2022] [Accepted: 09/29/2022] [Indexed: 06/17/2023]
Abstract
Cycling of carbon dioxide between the atmosphere and interior of rocky planets can stabilize global climate and enable planetary surface temperatures above freezing over geologic time. However, variations in global carbon budget and unstable feedback cycles between planetary sub-systems may destabilize the climate of rocky exoplanets toward regimes unknown in the Solar System. Here, we perform clear-sky atmospheric radiative transfer and surface weathering simulations to probe the stability of climate equilibria for rocky, ocean-bearing exoplanets at instellations relevant for planetary systems in the outer regions of the circumstellar habitable zone. Our simulations suggest that planets orbiting G- and F-type stars (but not M-type stars) may display bistability between an Earth-like climate state with efficient carbon sequestration and an alternative stable climate equilibrium where CO2 condenses at the surface and forms a blanket of either clathrate hydrate or liquid CO2. At increasing instellation and with ineffective weathering, the latter state oscillates between cool, surface CO2-condensing and hot, non-condensing climates. CO2 bistable climates may emerge early in planetary history and remain stable for billions of years. The carbon dioxide-condensing climates follow an opposite trend in pCO2 versus instellation compared to the weathering-stabilized planet population, suggesting the possibility of observational discrimination between these distinct climate categories.
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Affiliation(s)
- R. J. Graham
- Atmospheric, Oceanic and Planetary PhysicsDepartment of PhysicsUniversity of OxfordOxfordUK
| | - Tim Lichtenberg
- Atmospheric, Oceanic and Planetary PhysicsDepartment of PhysicsUniversity of OxfordOxfordUK
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Sakuraba H, Kurokawa H, Genda H, Ohta K. Numerous chondritic impactors and oxidized magma ocean set Earth's volatile depletion. Sci Rep 2021; 11:20894. [PMID: 34686749 PMCID: PMC8536732 DOI: 10.1038/s41598-021-99240-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 09/22/2021] [Indexed: 11/22/2022] Open
Abstract
Earth’s surface environment is largely influenced by its budget of major volatile elements: carbon (C), nitrogen (N), and hydrogen (H). Although the volatiles on Earth are thought to have been delivered by chondritic materials, the elemental composition of the bulk silicate Earth (BSE) shows depletion in the order of N, C, and H. Previous studies have concluded that non-chondritic materials are needed for this depletion pattern. Here, we model the evolution of the volatile abundances in the atmosphere, oceans, crust, mantle, and core through the accretion history by considering elemental partitioning and impact erosion. We show that the BSE depletion pattern can be reproduced from continuous accretion of chondritic bodies by the partitioning of C into the core and H storage in the magma ocean in the main accretion stage and atmospheric erosion of N in the late accretion stage. This scenario requires a relatively oxidized magma ocean (\documentclass[12pt]{minimal}
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\begin{document}$$f_{{\mathrm{O}}_2}$$\end{document}fO2 at the iron-wüstite buffer), the dominance of small impactors in the late accretion, and the storage of H and C in oceanic water and carbonate rocks in the late accretion stage, all of which are naturally expected from the formation of an Earth-sized planet in the habitable zone.
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Affiliation(s)
- Haruka Sakuraba
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan.
| | - Hiroyuki Kurokawa
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
| | - Hidenori Genda
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
| | - Kenji Ohta
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
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Thermodynamic and Energetic Limits on Continental Silicate Weathering Strongly Impact the Climate and Habitability of Wet, Rocky Worlds. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/1538-4357/ab9362] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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7
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Uncertainty Quantification in Planetary Thermal History Models: Implications for Hypotheses Discrimination and Habitability Modeling. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/1538-4357/ab822b] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Kump LR. Prolonged Late Permian-Early Triassic hyperthermal: failure of climate regulation? PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20170078. [PMID: 30177562 PMCID: PMC6127386 DOI: 10.1098/rsta.2017.0078] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 06/11/2018] [Indexed: 05/06/2023]
Abstract
The extreme warmth associated with the mass extinction at the Permian-Triassic boundary was likely produced by a rapid build-up of carbon dioxide in the atmosphere from the eruption and emplacement of the Siberian Traps. In comparison to another hyperthermal event, the Palaeocene-Eocene Thermal Maximum, the Permian-Triassic event, while leaving a similar carbon isotope record, likely had larger amounts of CO2 emitted and did not follow the expected time scale of climate recovery. The quantities and rates of CO2 emission likely exhausted the capacity of the long-term climate regulator associated with silicate weathering. Failure was enhanced by slow rock uplift and high continentality associated with the supercontinental phase of global tectonics at the time of the Siberian Traps eruption.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.
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Affiliation(s)
- Lee R Kump
- Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA
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9
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Lenardic A. The diversity of tectonic modes and thoughts about transitions between them. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20170416. [PMID: 30275163 PMCID: PMC6189555 DOI: 10.1098/rsta.2017.0416] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/09/2018] [Indexed: 05/18/2023]
Abstract
Plate tectonics is a particular mode of tectonic activity that characterizes the present-day Earth. It is directly linked to not only tectonic deformation but also magmatic/volcanic activity and all aspects of the rock cycle. Other terrestrial planets in our Solar System do not operate in a plate tectonic mode but do have volcanic constructs and signs of tectonic deformation. This indicates the existence of tectonic modes different from plate tectonics. This article discusses the defining features of plate tectonics and reviews the range of tectonic modes that have been proposed for terrestrial planets to date. A categorization of tectonic modes relates to the issue of when plate tectonics initiated on Earth as it provides insights into possible pre-plate tectonic behaviour. The final focus of this contribution relates to transitions between tectonic modes. Different transition scenarios are discussed. One follows classic ideas of regime transitions in which boundaries between tectonic modes are determined by the physical and chemical properties of a planet. The other considers the potential that variations in temporal evolution can introduce contingencies that have a significant effect on tectonic transitions. The latter scenario allows for the existence of multiple stable tectonic modes under the same physical/chemical conditions. The different transition potentials imply different interpretations regarding the type of variable that the tectonic mode of a planet represents. Under the classic regime transition view, the tectonic mode of a planet is a state variable (akin to temperature). Under the multiple stable modes view, the tectonic mode of a planet is a process variable. That is, something that flows through the system (akin to heat). The different implications that follow are discussed as they relate to the questions of when did plate tectonics initiate on Earth and why does Earth have plate tectonics.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.
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Affiliation(s)
- A Lenardic
- Department of Earth Science, Rice University, Houston, TX 77251-1892, USA
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Foley BJ. The dependence of planetary tectonics on mantle thermal state: applications to early Earth evolution. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20170409. [PMID: 30275160 PMCID: PMC6189558 DOI: 10.1098/rsta.2017.0409] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 07/24/2018] [Indexed: 05/23/2023]
Abstract
For plate tectonics to operate on a planet, mantle convective forces must be capable of forming weak, localized shear zones in the lithosphere that act as plate boundaries. Otherwise, a planet's mantle will convect in a stagnant lid regime, where subduction and plate motions are absent. Thus, when and how plate tectonics initiated on the Earth is intrinsically tied to the ability of mantle convection to form plate boundaries; however, the physics behind this process are still uncertain. Most mantle convection models have employed a simple pseudoplastic model of the lithosphere, where the lithosphere 'fails' and develops a mobile lid when stresses in the lithosphere reach the prescribed yield stress. With pseudoplasticity high mantle temperatures and high rates of internal heating, conditions relevant for the early Earth, impede plate boundary formation by decreasing lithospheric stresses, and hence favour a stagnant lid for the early Earth. However, when a model for shear zone formation based on grain size reduction is used, early Earth thermal conditions do not favour a stagnant lid. While lithosphere stress drops with increasing mantle temperature or heat production rate, the deformational work, which drives grain size reduction, increases. Thus, the ability of convection to form weak plate boundaries is not impeded by early Earth thermal conditions. However, mantle thermal state does change the style of subduction and lithosphere mobility; high mantle temperatures lead to a more sluggish, drip-like style of subduction. This 'sluggish lid' convection may be able to explain many of the key observations of early Earth crust formation processes preserved in the geologic record. Moreover, this work highlights the importance of understanding the microphysics of plate boundary formation for assessing early Earth tectonics, as different plate boundary formation mechanisms are influenced by mantle thermal state in fundamentally different ways.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.
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Affiliation(s)
- Bradford J Foley
- Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA
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Foley BJ, Smye AJ. Carbon Cycling and Habitability of Earth-Sized Stagnant Lid Planets. ASTROBIOLOGY 2018; 18:873-896. [PMID: 30035642 DOI: 10.1089/ast.2017.1695] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Models of thermal evolution, crustal production, and CO2 cycling are used to constrain the prospects for habitability of rocky planets, with Earth-like size and composition, in the stagnant lid regime. Specifically, we determine the conditions under which such planets can maintain rates of CO2 degassing large enough to prevent global surface glaciation but small enough so as not to exceed the upper limit on weathering rates provided by the supply of fresh rock, a situation which would lead to runaway atmospheric CO2 accumulation and an inhospitably hot climate. The models show that stagnant lid planets with initial radiogenic heating rates of 100-250 TW, and with total CO2 budgets ranging from ∼10-2 to 1 times Earth's estimated CO2 budget, can maintain volcanic outgassing rates suitable for habitability for ≈1-5 Gyr; larger CO2 budgets result in uninhabitably hot climates, while smaller budgets result in global glaciation. High radiogenic heat production rates favor habitability by sustaining volcanism and CO2 outgassing longer. Thus, the results suggest that plate tectonics may not be required for establishing a long-term carbon cycle and maintaining a stable, habitable climate. The model is necessarily highly simplified, as the uncertainties with exoplanet thermal evolution and outgassing are large. Nevertheless, the results provide some first-order guidance for future exoplanet missions, by predicting the age at which habitability becomes unlikely for a stagnant lid planet as a function of initial radiogenic heat budget. This prediction is powerful because both planet heat budget and age can potentially be constrained from stellar observations. Key Words: Exoplanets-Habitability-Stagnant lid tectonics-Carbon cycle-Volcanism. Astrobiology 18, 873-896.
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Affiliation(s)
- Bradford J Foley
- Department of Geosciences, Pennsylvania State University, University Park , Pennsylvania
| | - Andrew J Smye
- Department of Geosciences, Pennsylvania State University, University Park , Pennsylvania
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Constraining the climate and ocean pH of the early Earth with a geological carbon cycle model. Proc Natl Acad Sci U S A 2018; 115:4105-4110. [PMID: 29610313 PMCID: PMC5910859 DOI: 10.1073/pnas.1721296115] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The climate and ocean pH of the early Earth are important for understanding the origin and early evolution of life. However, estimates of early climate range from below freezing to over 70 °C, and ocean pH estimates span from strongly acidic to alkaline. To better constrain environmental conditions, we applied a self-consistent geological carbon cycle model to the last 4 billion years. The model predicts a temperate (0–50 °C) climate and circumneutral ocean pH throughout the Precambrian due to stabilizing feedbacks from continental and seafloor weathering. These environmental conditions under which life emerged and diversified were akin to the modern Earth. Similar stabilizing feedbacks on climate and ocean pH may operate on earthlike exoplanets, implying life elsewhere could emerge in comparable environments. The early Earth’s environment is controversial. Climatic estimates range from hot to glacial, and inferred marine pH spans strongly alkaline to acidic. Better understanding of early climate and ocean chemistry would improve our knowledge of the origin of life and its coevolution with the environment. Here, we use a geological carbon cycle model with ocean chemistry to calculate self-consistent histories of climate and ocean pH. Our carbon cycle model includes an empirically justified temperature and pH dependence of seafloor weathering, allowing the relative importance of continental and seafloor weathering to be evaluated. We find that the Archean climate was likely temperate (0–50 °C) due to the combined negative feedbacks of continental and seafloor weathering. Ocean pH evolves monotonically from 6.6−0.4+0.6 (2σ) at 4.0 Ga to 7.0−0.5+0.7 (2σ) at the Archean–Proterozoic boundary, and to 7.9−0.2+0.1 (2σ) at the Proterozoic–Phanerozoic boundary. This evolution is driven by the secular decline of pCO2, which in turn is a consequence of increasing solar luminosity, but is moderated by carbonate alkalinity delivered from continental and seafloor weathering. Archean seafloor weathering may have been a comparable carbon sink to continental weathering, but is less dominant than previously assumed, and would not have induced global glaciation. We show how these conclusions are robust to a wide range of scenarios for continental growth, internal heat flow evolution and outgassing history, greenhouse gas abundances, and changes in the biotic enhancement of weathering.
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Krissansen-Totton J, Catling DC. Constraining climate sensitivity and continental versus seafloor weathering using an inverse geological carbon cycle model. Nat Commun 2017; 8:15423. [PMID: 28530231 PMCID: PMC5458154 DOI: 10.1038/ncomms15423] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 03/27/2017] [Indexed: 11/09/2022] Open
Abstract
The relative influences of tectonics, continental weathering and seafloor weathering in controlling the geological carbon cycle are unknown. Here we develop a new carbon cycle model that explicitly captures the kinetics of seafloor weathering to investigate carbon fluxes and the evolution of atmospheric CO2 and ocean pH since 100 Myr ago. We compare model outputs to proxy data, and rigorously constrain model parameters using Bayesian inverse methods. Assuming our forward model is an accurate representation of the carbon cycle, to fit proxies the temperature dependence of continental weathering must be weaker than commonly assumed. We find that 15–31 °C (1σ) surface warming is required to double the continental weathering flux, versus 3–10 °C in previous work. In addition, continental weatherability has increased 1.7–3.3 times since 100 Myr ago, demanding explanation by uplift and sea-level changes. The average Earth system climate sensitivity is K (1σ) per CO2 doubling, which is notably higher than fast-feedback estimates. These conclusions are robust to assumptions about outgassing, modern fluxes and seafloor weathering kinetics. The influence of tectonics, continental weathering, and seafloor weathering in the geological carbon cycle remain unclear. Here, the authors develop a new carbon cycle model and, through comparison with proxy data, critically evaluate the influence of these components on carbon fluxes since 100 Ma.
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Affiliation(s)
- Joshua Krissansen-Totton
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, Washington 98195-1310, USA
| | - David C Catling
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, Washington 98195-1310, USA
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Future climate forcing potentially without precedent in the last 420 million years. Nat Commun 2017; 8:14845. [PMID: 28375201 PMCID: PMC5382278 DOI: 10.1038/ncomms14845] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Accepted: 02/06/2017] [Indexed: 11/08/2022] Open
Abstract
The evolution of Earth's climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm-2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm-2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth's long-term habitability. Humanity's fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.
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Komacek TD, Abbot DS. EFFECT OF SURFACE-MANTLE WATER EXCHANGE PARAMETERIZATIONS ON EXOPLANET OCEAN DEPTHS. THE ASTROPHYSICAL JOURNAL 2016; 832:54. [PMID: 30705445 PMCID: PMC6350802 DOI: 10.3847/0004-637x/832/1/54] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a "waterworld." On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. Here we explore how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady state after ~2 Gyr. Using these steady states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (≳0.3% of total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.
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Affiliation(s)
- Thaddeus D Komacek
- Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, Tucson, AZ, USA
| | - Dorian S Abbot
- Department of the Geophysical Sciences, University of Chicago, Chicago, IL, USA
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Abbot DS. ANALYTICAL INVESTIGATION OF THE DECREASE IN THE SIZE OF THE HABITABLE ZONE DUE TO A LIMITED CO 2 OUTGASSING RATE. THE ASTROPHYSICAL JOURNAL 2016; 827:117. [PMID: 30504962 PMCID: PMC6267982 DOI: 10.3847/0004-637x/827/2/117] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The habitable zone concept is important because it focuses the scientific search for extraterrestrial life and aids the planning of future telescopes. Recent work has shown that planets near the outer edge of the habitable zone might not actually be able to stay warm and habitable if CO2 outgassing rates are not large enough to maintain high CO2 partial pressures against removal by silicate weathering. In this paper, I use simple equations for the climate and CO2 budget of a planet in the habitable zone that can capture the qualitative behavior of the system. With these equations I derive an analytical formula for an effective outer edge of the habitable zone, including limitations imposed by the CO2 outgassing rate. I then show that climate cycles between a snowball state and a warm climate are only possible beyond this limit if the weathering rate in the snowball climate is smaller than the CO2 outgassing rate (otherwise stable snowball states result). I derive an analytical solution for the climate cycles including a formula for their period in this limit. This work allows us to explore the qualitative effects of weathering processes on the effective outer edge of the habitable zone, which is important because weathering parameterizations are uncertain.
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Affiliation(s)
- Dorian S Abbot
- Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
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SCALING THE EARTH: A SENSITIVITY ANALYSIS OF TERRESTRIAL EXOPLANETARY INTERIOR MODELS. ACTA ACUST UNITED AC 2016. [DOI: 10.3847/0004-637x/819/1/32] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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