Abstract
Seismic images of Earth’s interior have revealed two continent-sized anomalies with low seismic velocities, known as the large low-velocity provinces (LLVPs), in the lowermost mantle1. The LLVPs are often interpreted as intrinsically dense heterogeneities that are compositionally distinct from the surrounding mantle2. Here we show that LLVPs may represent buried relics of Theia mantle material (TMM) that was preserved in proto-Earth’s mantle after the Moon-forming giant impact3. Our canonical giant-impact simulations show that a fraction of Theia’s mantle could have been delivered to proto-Earth’s solid lower mantle. We find that TMM is intrinsically 2.0–3.5% denser than proto-Earth’s mantle based on models of Theia’s mantle and the observed higher FeO content of the Moon. Our mantle convection models show that dense TMM blobs with a size of tens of kilometres after the impact can later sink and accumulate into LLVP-like thermochemical piles atop Earth’s core and survive to the present day. The LLVPs may, thus, be a natural consequence of the Moon-forming giant impact. Because giant impacts are common at the end stages of planet accretion, similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
All data and parameters are available in the main text or the supplementary materials. The data that support the findings of this study are also available at https://doi.org/10.6084/m9.figshare.24013776.v1. Source data are provided with this paper.
Code availability
The author’s modified 2D Citcom code used in this study is available from https://figshare.com/projects/Yuan_Li_2022_NG/129185. The GIZMO code is made available at http://www.tapir.caltech.edu/~phopkins/Site/GIZMO.html. SWIFT is publicly available at http://swiftsim.com. WoMa is publicly available at https://github.com/srbonilla/WoMa, or the Python module can be installed directly with pip (https://pypi.org/project/woma/).
References
Garnero, E. J., McNamara, A. K. & Shim, S. H. Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle. Nat. Geosci. 9, 481–489 (2016).
Labrosse, S., Hernlund, J. W. & Coltice, N. A crystallizing dense magma ocean at the base of the Earth’s mantle. Nature 450, 866–869 (2007).
Canup, R. M. & Asphaug, E. Origin of the Moon in a giant impact near the end of the Earth’s formation. Nature 412, 708–712 (2001).
Kokubo, E. & Ida, S. Orbital evolution of protoplanets embedded in a swarm of planetesimals. Icarus 114, 247–257 (1995).
Cameron, A. G. W. & Ward, W. R. The origin of the Moon. Abstr. Lunar Planet. Sci. Conf. 7, 120–122 (1976).
Ringwood, A. E. Volatile and siderophile element geochemistry of the Moon: a reappraisal. Earth Planet. Sci. Lett. 111, 537–555 (1992).
Nie, N. X. & Dauphas, N. Vapor drainage in the protolunar disk as the cause for the depletion in volatile elements of the Moon. Astrophys. J. 884, L48 (2019).
Lee, C. T. A. et al. Upside-down differentiation and generation of a primordial lower mantle. Nature 463, 930–933 (2010).
Christensen, U. R. & Hofmann, A. W. Segregation of subducted oceanic crust in the convecting mantle. J. Geophys. Res. 99, 19867–19884 (1994).
Williams, C. D., Mukhopadhyay, S., Rudolph, M. L. & Romanowicz, B. Primitive helium is sourced from seismically slow regions in the lowermost mantle. Geochem. Geophys. Geosyst. 20, 4130–4145 (2019).
Mukhopadhyay, S. Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101–104 (2012).
Desch, S. J. & Robinson, K. L. A unified model for hydrogen in the Earth and Moon: no one expects the Theia contribution. Chemie der Erde 79, 125546 (2019).
Pepin, R. O. & Porcelli, D. Origin of noble gases in the terrestrial planets. Rev. Mineral. Geochem. 47, 191–246 (2002).
Burke, K., Steinberger, B., Torsvik, T. H. & Smethurst, M. A. Plume generation zones at the margins of large low shear velocity provinces on the core–mantle boundary. Earth Planet. Sci. Lett. 265, 49–60 (2008).
Will, P., Busemann, H., Riebe, M. E. I. & Maden, C. Indigenous noble gases in the Moon’s interior. Sci. Adv. 8, 1–9 (2022).
Stewart, S. et al. The shock physics of giant impacts: key requirements for the equations of state. AIP Conf. Proc. 2272, 080003 (2020).
Kegerreis, J. A., Eke, V. R., Massey, R. J., Sandnes, T. D. & Teodoro, L. F. A. Immediate origin of the Moon as a post-impact satellite. Astrophys. J. Lett. 937, L40 (2022).
Deng, H. et al. Enhanced mixing in Giant Impact simulations with a new Lagrangian method. Astrophys. J. 870, 127 (2019).
Deng, H. et al. Primordial Earth mantle heterogeneity caused by the Moon-forming Giant Impact? Astrophys. J. 887, 211 (2019).
Cottaar, S. & Lekic, V. Morphology of seismically slow lower-mantle structures. Geophys. J. Int. 207, 1122–1136 (2016).
Kegerreis, J. A. et al. Planetary giant impacts: convergence of high-resolution simulations using efficient spherical initial conditions and SWIFT. Mon. Not. R. Astron. Soc. 487, 5029–5040 (2019).
Deguen, R., Landeau, M. & Olson, P. Turbulent metal–silicate mixing, fragmentation, and equilibration in magma oceans. Earth Planet. Sci. Lett. 391, 274–287 (2014).
Dauphas, N., Burkhardt, C., Warren, P. H. & Fang-Zhen, T. Geochemical arguments for an Earth-like Moon-forming impactor. Philos. Trans. R. Soc. A 372, 20130244 (2014).
Pahlevan, K., Stevenson, D. J. & Eiler, J. M. Chemical fractionation in the silicate vapor atmosphere of the Earth. Earth Planet. Sci. Lett. 301, 433–443 (2011).
Meier, M. M. M., Reufer, A. & Wieler, R. On the origin and composition of Theia: constraints from new models of the Giant Impact. Icarus 242, 316–328 (2014).
Robinson, K. L. et al. Water in evolved lunar rocks: evidence for multiple reservoirs. Geochim. Cosmochim. Acta 188, 244–260 (2016).
Connolly, J. A. D. Computation of phase equilibria by linear programming: a tool for geodynamic modeling and its application to subduction zone decarbonation. Earth Planet. Sci. Lett. 236, 524–541 (2005).
Connolly, J. A. D. The geodynamic equation of state: what and how. Geochem. Geophys. Geosyst. 10, 1–19 (2009).
Stixrude, L. & Lithgow-Bertelloni, C. Thermodynamics of mantle minerals – II. Phase equilibria. Geophys. J. Int. 184, 1180–1213 (2011).
Nakajima, M. & Stevenson, D. J. Melting and mixing states of the Earth’s mantle after the Moon-forming impact. Earth Planet. Sci. Lett. 427, 286–295 (2015).
Gurnis, M. The effects of chemical density differences on convective mixing in the Earth’s mantle. J. Geophys. Res., Solid Earth 91, 11407–11419 (1986).
Tackley, P. J. in The Core‐Mantle Boundary Region (eds Gurnis, M., Wysession, M. E., Knittle, E. & Buffet, B. A.) 231–253 (American Geophysical Union, 1998).
Nakagawa, T., Tackley, P. J., Deschamps, F. & Connolly, J. A. D. The influence of MORB and harzburgite composition on thermo-chemical mantle convection in a 3-D spherical shell with self-consistently calculated mineral physics. Earth Planet. Sci. Lett. 296, 403–412 (2010).
Gu, T., Li, M., McCammon, C. & Lee, K. K. M. Redox-induced lower mantle density contrast and effect on mantle structure and primitive oxygen. Nat. Geosci. 9, 723–727 (2016).
Yuan, Q. & Li, M. Instability of the African large low-shear-wave-velocity province due to its low intrinsic density. Nat. Geosci. 15, 334–339 (2022).
McNamara, A. K. & Zhong, S. Thermochemical structures beneath Africa and the Pacific Ocean. Nature 437, 1136–1139 (2005).
O’Neill, C., Marchi, S., Zhang, S. & Bottke, W. Impact-driven subduction on the Hadean Earth. Nat. Geosci. 10, 793–797 (2017).
Hernlund, J. W. & Houser, C. On the statistical distribution of seismic velocities in Earth’s deep mantle. Earth Planet. Sci. Lett. 265, 423–437 (2008).
Lei, W. et al. Global adjoint tomography – model GLAD-M25. Geophys. J. Int. 223, 1–21 (2020).
Elkins-Tanton, L. T. Magma oceans in the inner Solar System. Annu. Rev. Earth Planet. Sci. 40, 113–139 (2012).
Abe, Y. Thermal and chemical evolution of the terrestrial magma ocean. Phys. Earth Planet. Inter. 1, 27–39 (1997).
Solomatov, V. S. in Treatise on Geophysics 1st edn, Vol. 9 (ed. Schubert, G.) 91–119 (Elsevier, 2007).
Maurice, M. et al. Onset of solid-state mantle convection and mixing during magma ocean solidification. J. Geophys. Res., Planets 122, 577–598 (2017).
Boukaré, C. E., Parmentier, E. M. & Parman, S. W. Timing of mantle overturn during magma ocean solidification. Earth Planet. Sci. Lett. 491, 216–225 (2018).
Labrosse, S., Morison, A., Deguen, R. & Alboussière, T. Rayleigh–Bénard convection in a creeping solid with melting and freezing at either or both its horizontal boundaries. J. Fluid Mech. 846, 5–36 (2018).
Agrusta, R. et al. Mantle convection interacting with magma oceans. Geophys. J. Int. 220, 1878–1892 (2020).
Morison, A., Labrosse, S., Deguen, R. & Alboussière, T. Timescale of overturn in a magma ocean cumulate. Earth Planet. Sci. Lett. 516, 25–36 (2019).
Becker, T. W., Kellogg, J. B. & O’Connell, R. J. Thermal constraints on the survival of primitive blobs in the lower mantle. Earth Planet. Sci. Lett. 171, 351–365 (1999).
Lock, S. J., Bermingham, K. R., Parai, R. & Boyet, M. Geochemical constraints on the origin of the Moon and preservation of ancient terrestrial heterogeneities. Space Sci. Rev. 216, 1–46 (2020).
Ballmer, M. D., Lourenço, D. L., Hirose, K., Caracas, R. & Nomura, R. Reconciling magma-ocean crystallization models with the present-day structure of the Earth’s mantle. Geochem. Geophys. Geosyst. 18, 2785–2806 (2017).
Maas, C. & Hansen, U. Dynamics of a terrestrial magma ocean under planetary rotation: a study in spherical geometry. Earth Planet. Sci. Lett. 513, 81–94 (2019).
Williams, C. D. & Mukhopadhyay, S. Capture of nebular gases during Earth’s accretion is preserved in deep-mantle neon. Nature 565, 78–81 (2019).
Mundl-Petermeier, A. et al. Temporal evolution of primordial tungsten-182 and 3He/4He signatures in the Iceland mantle plume. Chem. Geol. 525, 245–259 (2019).
Li, M., McNamara, A. K. & Garnero, E. J. Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs. Nat. Geosci. 7, 366–370 (2014).
Mulyukova, E., Steinberger, B., Dabrowski, M. & Sobolev, S. V. Survival of LLSVPs for billions of years in a vigorously convecting mantle: replenishment and destruction of chemical anomaly. J. Geophys. Res., Solid Earth 120, 3824–3847 (2015).
Jackson, M. G. et al. Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling. Proc. Natl Acad. Sci. USA 117, 30993–31001 (2020).
Brown, J. M. & Shankland, T. J. Thermodynamic parameters in the Earth as determined from seismic profiles. Geophys. J. R. Astron. Soc. 66, 579–596 (1981).
Stacey, F. D. A thermal model of the earth. Phys. Earth Planet. Inter. 15, 341–348 (1977).
Canup, R. M., Barr, A. C. & Crawford, D. A. Lunar-forming impacts: high-resolution SPH and AMR-CTH simulations. Icarus 222, 200–219 (2013).
Hosono, N., Saitoh, T. R., Makino, J., Genda, H. & Ida, S. The Giant Impact simulations with density independent smoothed particle hydrodynamics. Icarus 271, 131–157 (2016).
Reinhardt, C. & Stadel, J. Numerical aspects of Giant Impact simulations. Mon. Not. R. Astron. Soc. 467, 4252–4263 (2017).
Ruiz-Bonilla, S. et al. Dealing with density discontinuities in planetary SPH simulations. Mon. Not. R. Astron. Soc. 512, 4660–4668 (2022).
Hosono, N. & Karato, S. The influence of equation of state on the Giant Impact simulations. J. Geophys. Res., Planets 127, 1–18 (2022).
Hosono, N. et al. Unconvergence of very-large-scale Giant Impact simulations. Publ. Astron. Soc. Jpn 69, 1–11 (2017).
Meier, T., Reinhardt, C. & Stadel, J. G. The EOS/resolution conspiracy: convergence in proto-planetary collision simulations. Mon. Not. R. Astron. Soc. 1816, 1806–1816 (2021).
Raskin, C. & Owen, J. M. Examining the accuracy of astrophysical disk simulations with a generalized hydrodynamical test problem. Astrophys. J. 831, 26 (2016).
Gabriel, T. S. J. & Allen-Sutter, H. Dependencies of mantle shock heating in pairwise accretion. Astrophys. J. Lett. 915, L32 (2021).
Frontiere, N., Raskin, C. D. & Owen, J. M. CRKSPH – a conservative reproducing kernel smoothed particle hydrodynamics scheme. J. Comput. Phys. 332, 160–209 (2017).
Rosswog, S. Astrophysical smooth particle hydrodynamics. New Astron. Rev. 53, 78–104 (2009).
Schaller, M. et al. SWIFT: SPH with inter-dependent fine-grained tasking. In Astrophysics Source Code Library, ascl-1805 (2018).
Ruiz-Bonilla, S., Eke, V. R., Kegerreis, J. A., Massey, R. J. &Teodoro, L. F. A. The effect of pre-impact spin on the Moon-forming collision. Mon. Not. R. Astron. Soc. 2870, 2861–2870 (2021).
Canup, R. M. Forming a Moon with an Earth-like composition via a giant impact. Science 338, 1052–1056 (2012).
Hopkins, P. F. A new class of accurate, mesh-free hydrodynamic simulation methods. Mon. Not. R. Astron. Soc. 450, 53–110 (2015).
Thompson, S. L. & Lauson, H. S. Improvements in the Chart D Radiation—Hydrodynamic Code. III. Revised Analytic Equation of State. Sandia Report SC-RR-71 0174 (1972).
Melosh, H. J. A hydrocode equation of state for SiO2. Meteorit. Planet. Sci. 42, 2079–2098 (2007).
Fiquet, G. et al. Melting of peridotite to 140 gigapascals. Science 329, 1516–1518 (2010).
Andrault, D. et al. Solidus and liquidus profiles of chondritic mantle: implication for melting of the Earth across its history. Earth Planet. Sci. Lett. 304, 251–259 (2011).
Abe, Y. in Evolution of the Earth and Planets (eds Takahashi, E., Jeanloz, R. & Rubie, D.) 41–54 (American Geophysical Union, 1993).
Miyazaki, Y. & Korenaga, J. On the timescale of magma ocean solidification and its chemical consequences: 2. Compositional differentiation under crystal accumulation and matrix compaction. J. Geophys. Res., Solid Earth 124, 3399–3419 (2019).
Nomura, R. et al. Spin crossover and iron-rich silicate melt in the Earth’s deep mantle. Nature 473, 199–202 (2011).
Andrault, D. et al. Solid–liquid iron partitioning in Earth’s deep mantle. Nature 487, 354–357 (2012).
Moresi, L. N. & Solomatov, V. S. Numerical investigation of 2D convection with extremely large viscosity variations. Phys. Fluids 7, 2154–2162 (1995).
Farrell, K. A. O. & Lowman, J. P. Emulating the thermal structure of spherical shell convection in plane-layer geometry mantle convection models. Phys. Earth Planet. Inter. 182, 73–84 (2010).
Tackley, P. J. & King, S. D. Testing the tracer ratio method for modeling active compositional fields in mantle convection simulations. Geochem. Geophys. Geosyst. 4, 1–15 (2003).
Schaller, M. et al. Swift: a modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications. Preprint at http://arxiv.org/abs/2305.13380 (2023).
Hirth, G. & Kohlstedt, D. L. Water in the oceanic upper mantle: implications for rheology, melt extraction and the evolution of the lithosphere. Earth Planet. Sci. Lett. 144, 93–108 (1996).
Dziewonski, A. M. & Anderson, D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981).
Acknowledgements
We thank M. Gurnis, D. Stevenson, R. Canup, P. Olson, S. Stewart, M. Zolotov, T. Becker, M. Jackson, S.-H. Shim, D. Grady, R. Shi and S. Yuan for their support, discussions and insights. The numerical models were performed on the Agave cluster at Arizona State University. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This work is supported by National Science Foundation grants EAR-1849949, EAR-1855624 and EAR-2216564. Q.Y. acknowledges support from the O. K. Earl Postdoctoral Fellowship at Caltech. T.S.J.G. recognizes support from the U.S. Geological Survey, Astrogeology Science Center. J.A.K. acknowledges support from a NASA Postdoctoral Program Fellowship, administered by Oak Ridge Associated Universities. Y.M. acknowledges a Stanback Postdoctoral Fellowship from the Caltech Center for Comparative Planetary Evolution. V.R.E. is supported by Science and Technology Facilities Council (STFC) grant ST/T000244/1. The MFM giant-impact simulations were performed on the Piz Daint supercomputer of the Swiss Nation Supercomputing Centre and the local cluster of the Shanghai Astronomical Observatory. The research in this paper made use of the SWIFT open-source simulation code70,85, v.0.9.0. This work used the DiRAC@Durham facility managed by the Institute for Computational Cosmology on behalf of the STFC DiRAC High-Performance Computing Facility (www.dirac.ac.uk). The equipment was funded by capital funding from the Department for Business, Energy and Industrial Strategy via STFC capital grants ST/K00042X/1, ST/P002293/1, ST/R002371/1 and ST/S002502/1, Durham University and STFC operations grant ST/R000832/1. DiRAC is part of the National e-Infrastructure.
Author information
Authors and Affiliations
Contributions
Q.Y. and E.J.G. conceptualized the initial idea. Q.Y., M.M.L. and E.J.G. designed the study. Q.Y. performed and analysed the geodynamic models with supervision from M.M.L. S.J.D. constrained the impact scenario and provided the composition of Theia. B.K. and Q.Y. computed the thermodynamic and seismic calculations. H.P.D., J.A.K. and V.R.E. performed the impact simulations and analysed the results. T.S.J.G. performed independent verifications of the SPH results and consulted on the SPH numerics. Y.M. developed the thermal evolution model. P.D.A. examined the fragmentation, dilution effect and magma mixing associated with the impact. All authors contributed to the writing and editing of the manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature thanks Stéphane Labrosse and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Extended Data Fig. 1 Entropy profile (blue, in Jkg−1K−1) of mantle material in the post-impact Earth for our impact model using the meshless finite mass (MFM) method18.
Extended Data Fig. 2 Phase diagrams of the bulk silicate Earth (a), Theia_1 (b), Theia_2 (c) and Theia_3 (d) with geotherm from ref. 57.
The FeO contents of Theia are 13 wt% (Theia_1), 15 wt% (Theia_2), and 17 wt% (Theia_3), respectively. Phase equilibria were calculated using Perple_X27,28 with thermodynamic data from ref. 29. St: stishovite, Fp: ferropericlase, Ring: ringwoodite, Wad: wadsleyite, Ol: olivine, Cpx: clinopyroxene, Brg: bridgmanite, Gt: garnet, CaPv: davemaoite.
Extended Data Fig. 3 Phase diagrams of the bulk silicate Earth (a), Theia_1 (b), Theia_2 (c) and Theia_3 (d) with geotherm from ref. 58.
The FeO contents of Theia are 13 wt% (Theia_1), 15 wt% (Theia_2), and 17 wt% (Theia_3), respectively. Phase equilibria were calculated using Perple_X27,28 with thermodynamic data from ref. 29. Fp: ferropericlase, Wad: wadsleyite, Ol: olivine, Cpx: clinopyroxene, Brg: bridgmanite, Gt: garnet, CaPv: davemaoite.
Extended Data Fig. 4 Density difference between Theia mantle material and the bulk silicate Earth as a function of pressure.
Extended Data Fig. 5 One numerical experiment showing that dense TMM sinks to the CMB before upper mantle materials mix with lower mantle materials.
a-d, Snapshots of the temperature fields (a, c) and compositional fields (b, d) at 0.00 Myr (a-b) and 27.36 Myr (c-d). At t = 0.00, random TMM blobs are placed in the lower mantle (b). After 27.36 Myr, the TMM blobs reach the CMB (d) whereas there is little mixing between the upper mantle and lower mantle (c).
Supplementary information
Supplementary Video 1
A canonical giant-impact simulation using the MFM method shows the preservation of a mostly solid lower layer in Earth’s mantle after the impact. Model evolution spans 13.1 h after the giant impact, and the entropy unit is MJ K−1 kg−1.
Supplementary Video 2
A canonical giant-impact simulation using the SPH method, highlighting the preservation of a mostly solid lower layer in Earth’s mantle after the impact event. Entropy unit is kJ K−1 kg−1.
Supplementary Video 3
Reference case of a successful mantle convection model showing that the random spheres of solid TMM in the lower layer of Earth’s mantle quickly descend to the lowermost mantle and are later shaped into isolated thermochemical piles (large low-velocity provinces in the models) by mantle convection after Earth’s history.
Supplementary Video 4
Mantle convection in case 2 showing that a less dense TMM will be mostly entrained away in the background mantle.
Supplementary Video 5
Mantle convection in case 3 showing that the 3.5% denser TMM can sink and survive Earth’s 4.5 Gyr convective history.
Supplementary Video 6
Mantle convection in case 4 showing that a TMM with an end-member density of 5% can still sink and survive Earth’s 4.5 Gyr convective history as isolated thermochemical piles.
Supplementary Video 7
Mantle convection in case 5 showing that a half-sized TMM will not be able to survive Earth’s 4.5 Gyr convective history.
Supplementary Video 8
Mantle convection in case 6 showing that a TMM enriched in radioactive elements can sink and survive Earth’s 4.5 Gyr convective history.
Supplementary Video 9
Mantle convection in case 7 showing that a higher temperature-dependent viscosity does not affect our convection results.
Supplementary Video 10
Mantle convection in case 8 showing that a periodic side-boundary condition does not affect our numerical results.
Supplementary Video 11
Mantle convection in case 9 showing that a different initial temperature does not affect our convection results.
Rights and permissions
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
Yuan, Q., Li, M., Desch, S.J. et al. Moon-forming impactor as a source of Earth’s basal mantle anomalies. Nature 623, 95–99 (2023). https://doi.org/10.1038/s41586-023-06589-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41586-023-06589-1
This article is cited by
-
Don’t judge the Moon’s interior by its cover
Nature Geoscience (2024)
-
Strange blobs in Earth’s mantle are relics of a massive collision
Nature (2023)
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.