Published or In Press:

Underlined: Principal Investigator

Bold: Lab Member at the time

Asterisk: Student or post-doc co-author at time of publication



86. Rico, K.I.*, Sheldon, N.D., Kinsman-Costello, L.E., 2020. Associations between redox-sensitive trace metals and microbial communities in a Proterozoic ocean analogue. Geobiology, doi: 10.1111/gbi.12388

85. Hren, M.T., Sheldon, N.D., 2020. Terrestrial microbialites provide constraints on the Mesoproterozoic atmosphere. The Depositional Record, 6(1), 4-20. doi: 10.1002/dept2.79


84. Sheldon, N.D., Smith, S.Y., Stein, R.A.*, Ng, M., 2019, Carbon isotope ecology of gymnosperms and implications for paleoclimatic and paleoecological studies. Global Planetary Change, 103060.

83. Colwyn, D. A., Sheldon, N.D., Maynard, J.B., Gaines, R., Hofmann, A., Wang, X., Gueguen, B., Asael, D., Reinhard, C.T., Planavsky, N.J., 2019. A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic. Geobiology, 17(6), 579-593.

82. Gallagher, T.*, Hren, M.T., Sheldon, N.D., 2019. The effect of soil temperature seasonality on climate reconstructions from paleosols. American Journal of Science, 319(7), 549-581.

81. Stein, R.A.*, Sheldon, N.D., Smith, S.Y., 2019. Rapid response to anthropogenic climate change by Thuja occidentalis: implications for past climate reconstructions and future climate predictions. PeerJ, (in press). doi: tbd.

80. Rico, K.*, Sheldon, N.D., Gallagher, T.*, Chappaz, A., 2019. Redox chemistry and molybdenum burial in a Mesoproterozoic lake. Geophysical Research Letters, 46, 5871-5878. doi: 10.1029/2019GL083316.

79. Tessin, A.*, Schroeder-Adams, C., Elderbak, K., Sheldon, N.D., Hendy, I., 2019, Local versus seaway-wide trends in deoxygenation in the Late Cretaceous Western Interior Seaway: GSA Bulletin, 131, 1017-1030. doi: 10.1130/B32981.1

79. Rico, K.*, Sheldon, N.D., 2019. Nutrient and iron cycling in a modern analogue for the redoxcline of a Proterozoic ocean shelf. Chemical Geology, 511: 42-50. doi: 10.1016/j.chemgeo.2019.02.032

77. Tessin, A.*, Chappaz, A., Hendy, I., & Sheldon, N.D. 2019. Molybdenum speciation as a paleo-redox proxy: A case study from Late Cretaceous Western Interior Seaway black shales. Geology,47(1), 59-62. doi: 10.1130/G45785.1

76. Hyland, E.G.*, Sheldon, N.D., Smith, S.Y., Stromberg, C.A.E., 2019. Late Miocene rise and fall of C4 grasses in the western United States linked to aridification and uplift: GSA Bulletin, 131, (1-2) 224-234. doi: 10.1130/B32009.1


75. Sheldon, N.D., 2018. Using carbon isotope equilibrium to screen pedogenic carbonate oxygen isotopes: implications for paleoaltimetry and paleotectonic studies: Geofluids, 2018(5975801), 1-11. doi: 10.1155/2018/5975801

74. Hyland, E.G., Sheldon, N.D., 2018. Comment on “Paleosol-based paleoclimate reconstruction of the Paleocene-Eocene Thermal Maximum, northern Argentina” by Andrews, E., White, T., del Papa, C. [Palaeogeography, Palaeoclimatology, Palaeoecology 471, 181-195]: Palaeogeography, Palaeoclimatology, Palaeoecology, doi: 10.1016/j.paleo.2017.05.031

73. Hyland, E.G., Huntington, K.W., Sheldon, N.D., Reichgelt, T., 2018, Temperature seasonality in the North American continental interior during the Early Eocene Climatic Optimum: Climate of the Past 14, 1391-1404. doi: 10.5194/cp-14-1391-2018

72. Planavsky, N.J., Cole, D.B.*, Isson, T.T.*, Reinhard, C.T., Crockford, P.W.*, Sheldon, N.D., Lyons, T.W., 2018, A case for low atmospheric oxygen levels during Earth’s middle history: Emerging Topics in Life Sciences 2, 149–159. doi: 10.1042/ETLS20170161


71. Harris, E.B.*, Stromberg, C.A.E., Sheldon, N.D., Smith, S.Y., Vilhena, D., 2017, Vegetation response during the lead-up to the middle Miocene warming event in the Northern Rocky Mountains, USA: Palaeogeography, Palaeoclimatology, Palaeoecology 485, 401–415.  doi: 10.1016/j.paleo.2017.150

70. Tessin, A.*, Bianchi, T.S., Sheldon, N.D., Hendy, I., Hutchings, J., Arnold, T.E., 2017, Organic matter source and thermal maturity within the Late Cretaceous Niobrara Formation, U.S. Western Interior: Marine and Petroleum Geology 86, 812-822. doi: 10.1016/j.marpetgeo.2017.06.041

69. Griffith, D.M.*, Cotton, J.M., Powell, R.J., Sheldon, N.D., Still, C.J. 2017, Multi-century stasis in C3 and C4 grass distributions across the contiguous United States since the industrial revolution: Journal of Biogeography 44, 2564-2574. doi: 10.1111/jbi.13061

68. Gallagher, T.M.*, Sheldon, N.D., Mauk, J.L., Petersen, S.V.*, Gueneli, N.*, and Brocks, J.J., Constraining the thermal history of the North America Midcontinent Rift System using carbonate clumped isotopes and organic thermal maturity indices: Precambrian Research, 294: 53-66. doi: 10.1016/j.precamres.2016.255

67. Kinsman-Costello, L.E.*, Sheik, C.S., Sheldon, N.D., Burton, G.A., Costello, D.M., Marcus, D.*, Den Uyl, P.A.*, Dick, G.J., 2017, Groundwater shapes sediment biogeochemistry and microbial diversity in a submerged Great Lake sinkhole: Geobiology 15, 225-239. doi:10.1116/2017.03.022.

66. Harris, E.B.*, Strömberg, C.A.E., Sheldon, N.D., Smith, S.Y., Ibanez-Mejia, M., 2017, Revised chronostratigraphy and biostratigraphy of the early-middle Miocene Railroad Canyon Section of central-eastern Idaho: GSA Bulletin 129, 1241-1251. doi: 10.1130/B31655.2.

65. Fiorella, R.P.*, Sheldon, N.D., Equable end Mesoproterozoic climate in the absence of high CO2: Geology 45, 231-234. doi: 10.1130/B38682.1

64. Hyland, E.G.*, Sheldon, N.D., Cotton, J.M., 2017, Constraining the EECO: a terrestrial interhemispheric comparison: GSA Bulletin 129, 244–252. doi: 10.1130/B31493.1


63. Peterson, S.V.*, Tabor, C.R.*, Lohmann, K.C., Poulsen, C.J., Meyer, K.W.*, Carpenter, S.J., Erickson, J.M., Matsunaga, K.K.S.*, Smith, S.Y., Sheldon, N.D., 2016, Temperature and salinity of the Late Cretaceous Western Interior Seaway: Geology 44, 903–906, doi: 10.1130/G38311.1

62. Gallagher, T.G.*, Sheldon, N.D., 2016, Combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation: Chemical Geology 435, 79–91. doi: 10.1016/j.chemgeo.2016.04.023

61. Tessin, A.*, Sheldon, N.D., Hendy, I., Chappaz, A., 2016, Iron limitation in the Western Interior Seaway during the late Cretaceous OAE 3 and its role in phosphorus recycling and enhancing organic matter preservation: Earth and Planetary Science Letters 449, 135–144.

60. Mitchell, R.L.*, Sheldon, N.D., 2016, Sedimentary provenance and weathering processes in the 1.1 Ga Midcontinental Rift of the Keweenaw Peninsula, Michigan, USA: Precambrian Research 275, 225–250. doi: 10.1016/j.precamres.2016.01.017

59. Hyland, E.G.*, Sheldon, N.D., 2016, Examining the spatial consistency of paleosol proxies: implications for paleoclimatic and paleoenvironmental reconstructions in terrestrial sedimentary basins: Sedimentology 63, 959-971. doi: 10.1111/sed.12245

58. Retallack, G.J., Gavin, D.G., Davis, E.B., Sheldon, N.D., Erlandson, J.M., Reed, M.H., Bestland, E.A., Roering, J.J., Carson, R.J., and Mitchell, R.B., 2016), Oregon 2100: projected and climatic and ecological changes. University of Oregon Museum of Natural and Cultural History Bulletin, no. 26, p. 1–21.

57. Sheldon, N.D., Grimes, S.T., Hooker, J.J., Collinson, M.E., Bugler, M.J., Hren, M.T., Price, G.D., Sutton, P.A., 2016, Coupling of marine and continental oxygen isotope records during the Eocene-Oligocene transition: GSA Bulletin 128, 502–510. doi: 10.1130/B31315.1


56. Smith, S.Y., Manchester, S.R., Samant, B., Mohabey, D.M., Wheeler, E., Baas, P., Kapgate, D., Srivastava, R., Sheldon, N.D., 2015, Integrating paleobotanical, paleosol, and stratigraphic data to study critical transitions: a case study from the Late Cretaceous-Paleocene of India: Paleontological Society Special Paper 25, pp. 137–167.

55. Chen, S.T.*, Smith, S.Y., Sheldon, N.D., and Strömberg, C.A.E., 2015, Regional-scale variability in the spread of grasslands in the late Miocene: Palaeogeography, Palaeoclimatology, Palaeoecology 437, 42–52. doi:10.1016/j.paleo.2015.07.020

54. Tessin, A.*, Hendy, I.G., Sheldon, N.D., Sageman, B., 2015, Redox controlled preservation of organic matter during “OAE3” within the Western Interior Seaway. Paleoceanography 30, 702-717. doi: 10.1002/2014PA002729

53. Hyland, E.G.*, Sheldon, N.D., Van der Voo, R., Badgley, C.E., Abrajevitch, A., 2015, A new paleoprecipitation proxy based on soil magnetic properties: implications for expanding paleoclimate reconstructions: GSA Bulletin 127, 975–981. doi: 10.1130/B31207.1

52. Cotton, J.M.*, Sheldon, N.D., Hren, M.T., and Gallagher, T.M.*, 2015. Positive feedback drives carbon release from soils to atmosphere during Paleocene/Eocene warming: American Journal of Science 315, 337–361. doi: 10.2475/04.2015.03

51. Hyland, E.G.*, Sheldon, N.D., Cotton, J.M.*, 2015, Terrestrial evidence for a two-stage mid-Paleocene biotic event: Palaeogeography, Palaeoclimatology, Palaeoecology, 417, 371–378. doi:10.1016/j.palaeo.2014.09.031


50. Cotton, J.M.*, Hyland, E.G.*, and Sheldon, N.D., 2014, Multiproxy evidence for tectonic control on the expansion of C4 grasses in northwest Argentina: Earth and Planetary Science Letters 395, 41–50. doi: 10.1016/j.epsl.2014.03.014

49. Sheldon, N.D., Chakrabarti, R., Retallack, G.J., and Smith, R.M.H., 2014, Contrasting geochemical signatures on land from the Middle and Late Permian extinction events: Sedimentology 61, 1812–1829. doi: 10.1111/sed.12117


48. Sheldon, N.D. 2013, Causes and consequences of low atmospheric CO2 levels in the Mesoproterozoic: Chemical Geology 362 , 224-231. doi: 10.1016/j.chemgeo.2013.09.006

47. Cotton, J.M*, Jeffery, M. L.*, and Sheldon, N. D. 2013, Climate controls on soil respired CO2 in the United States: Implications for 21st century chemical weathering rates in temperate and arid ecosystems: Chemical Geology 358, 37-45. Doi: 10.1016/j.chemgeo.08.048

46. Hren, M.*, Sheldon, N.D., Bugler, M.J., Grimes, S.T., Hooker, J.J., Collinson, M.E., and Lohmann, K.C., 2013, Terrestrial cooling in northern Europe during the Eocene-Oligocene transition: Proceedings of the National Academy of Sciences 110, 7562–7567. doi: 10.1073/pnas.1210930110

45. Gallagher, T.M.*, and Sheldon, N.D., 2013, A new paleothermometer for forest paleosols and its implications for Cenozoic climate: Geology 41, 647–650. doi:10.1130/B34074

44. Hyland, E.G.*, Smith, S.Y., Sheldon, N.D., 2013, Representational bias in phytoliths from modern soils of central North America: implications for paleovegetation reconstructions: Palaeogeography, Palaeoclimatology, Palaeoecology 374, 338–348. doi: 10.1016.j.palaeo.2013.01.026

43. Hyland, E.G.*, Sheldon, N.D., and Fan, M., 2013, Continental record of the Early Eocene Climatic Optimum: GSA Bulletin 125, 1338–1348. doi: 10.1130/B30761.1

42. Cotton, J.M.*, and Sheldon, N.D., 2013, Using stable isotopes to teach agricultural sustainability in both high- and low-enrollment courses: Journal of Geoscience Education 61, 59–67 doi: 10.5408/12-309.1

41. Sheldon, N.D., and Tabor, N.J., 2013, Using paleosols to understand paleo-carbon burial: SEPM Special Paper 104 (Eds. S. Driese and L. Nordt), 71–78. doi: 10.2110/sepmsp.104.11

40. Tabor, N., Myers, T., Gulbranson, E., Rasmussen, C., and Sheldon, N.D., 2013, Carbon stable isotope composition of modern calcareous soil profiles in California: implications for CO2 reconstructions from calcareous paleosols: SEPM Special Paper 104 (Eds. S. Driese and L. Nordt), 17–34. doi: 10.2110/sepmsp.104.07

39. Hyland, E.G.*, and Sheldon, N.D., 2013, Coupled CO2-climate response during the Early Eocene Climatic Optimum (Green River Basin, Wyoming, USA): Palaeogeography, Palaeoclimatology, Palaeoecology 369, 125–135. doi: 10.1016/j.palaeo.2012.10.011


38. Sheldon, N.D., 2012, Microbially induced sedimentary structures in the ca. 1100 Ma terrestrial Midcontinent Rift of North America, in, Noffke, N., and Chafetz, H., eds., Microbial Mats in Siliciclastic Systems Through Time: SEPM Special Publication 101, p. 153–162. doi: 10.2110/sepmsp.101.153

37 De la Horra, R., Galán-Abellán, A.B., López-Gómez, J., Sheldon, N.D., Barrenechea, J.F., Luque, F.J., Arche, A., and Benito, M.I., 2012, Paleoenvironmental changes during the continental end-Guadalupian transition at the SE Iberian Ranges, Spain: Global and Planetary Change 94, 46–61. doi: 10.1016/j.gloplacha.2012.06.008

36. Cotton, J.M.*, and Sheldon, N.D. 2012, New constraints on using paleosols to reconstruct atmospheric pCO2: GSA Bulletin 124, 1411–1423. doi:10.1130/B30607.1

35. Miller, L.*, Smith, S.Y., Sheldon, N.D., and Strömberg, C.A.E., 2012, Eocene vegetation dynamics in Montana inferred from a high-resolution phytolith record: GSA Bulletin 124, 1577–1589. doi: 10.1130/B30548.1

34. Hren, M.T.*, and Sheldon, N.D., 2012, Temporal variations in lake water temperature: paleoenvironmental implications of lake carbonate δ18O and temperature records: Earth and Planetary Science Letters 337, 77–84. doi: 10.1016/j.epsl.2012.05.19.

33. Cotton, J.M.*, Sheldon, N.D., and Strömberg, C.A.E., 2012, High-resolution isotopic record of C4 photosynthesis in a Miocene grassland: Palaegeography, Palaeoclimatology, Palaeoecology 337-338, 88–98. doi: 10.1016/j.palaeo.2012.03.035.

32. Voorhies, A.A.*, Biddanda, B., Kendall, S.T., Jain, S.*, Marcus, D.N.*, Nold, S.C., Sheldon, N.D., and Dick, G.J., 2012. Cyanobacterial life at low O2: community genomics and function reveal extremely low diversity and metabolic versatility of a benthic cyanobacterial mat: Geobiology 10, 250–267, doi: 10.1111/j.l472-4669.2012.00322.x

31. Sheldon, N.D., Costa, E.*, Cabrera, L., and Garcés, M., 2012, Continental climatic and weathering response to the Eocene-Oliogocene transition: Journal of Geology 120, 227–236. doi: 10.1086/663984

30. Gutierrez, K.A.*, and Sheldon, N.D., 2012, Paleoenvironmental reconstruction of Middle Jurassic dinosaur habitats of the Vega Formation, Asturias, Spain: GSA Bulletin 124, 596–610. doi: 10.1130/B30285.1


29. Driese, S.G., Jirsa, M.A., Ren, M., Sheldon, N.D., Brantley, S.L., Parker, D., and Schmitz, M., 2011, Neoarchean paleoweathering of tonalite and metabasalt: implications for reconstructions of 2.69 Ga early terrestrial ecosystems and paleoatmospheric chemistry: Precambrian Research 189, 1–17. doi: 10.1016/j.precamres.2011.04.003

28. Retallack, G.J., Sheldon, N.D., Carr, P.F., Fanning, M., Thompson, C.A., Williams, M.L., Jones, B.G., and Hutton, A., 2011, Multiple Early Triassic greenhouse crises impeded recovery from Late Permian mass extinction: Palaeogeography, Palaeoclimatology, Palaeoecology 308, 233–251.doi:10.1016/j.palaeo.2010.09.022


27. Mitchell, R.L.*, and Sheldon, N.D., 2010, ~1100 Ma Sturgeon Falls paleosol revisited: implications for Mesoproterozoic weathering environments and atmospheric CO2 levels: Precambrian Research 183, 738–748. doi: 10.1016/j.precamres.2010.09.003

26. Hamer, J.M.M.*, and Sheldon, N.D., 2010, Neoichnology at lake margins: Sedimentary Geology 228, 319–327. doi: 10.1016/j.sedgeo.2010.06.02

25. Sheldon, N.D., Hamer, J.M.M.*, 2010, Evidence for an early sagebrush ecosystem in the latest Eocene of Montana: Journal of Geology 118, 435–445. doi: 10.1086/652660


24. Hooker, J.J., Grimes, S.T., Mattey, D.P., Collinson, M.E., and Sheldon, N.D., 2009, Refined correlation of the UK Late Eocene – Early Oligocene Solent Group and of its climate history: GSA Special Paper 452, p. 179–196. doi: 10.1130/2009.2452(12)

23. Sheldon, N.D., Mitchell, R.L.*, Collinson, M.E., and Hooker, J.J., 2009, Eocene-Oligocene transition paleoclimatic and paleoenvironmental record from the Isle of Wight (UK): GSA Special Paper 452, p. 249–260. doi: 10.1130/2009.2452(16)

22. Sheldon, N.D., 2009, Non-marine records of climatic change across the Eocene-Oligocene transition: GSA Special Paper 452, p. 241–248. doi: 10.1130/2009.2452(15)

21. Sheldon, N.D., and Tabor, N. J., 2009, Quantitative Paleoenvironmental and Paleoclimatic Reconstruction Using Paleosols: Earth-Science Reviews 95, p. 1-52. doi: 10.1016/j.earscirev.2009.03.004

20. Mitchell, R.L.*, Sheldon, N.D., 2009, Weathering and paleosol formation in the 1.1. Ga Keweenawan Rift: Precambrian Research 168, 271–283. doi: 10.1016/j.precamres.2008.09.013


19. Hamer, J.M.M.*, Sheldon, N.D., and Nichols, G.J., 2007, Global aridity during the Early Miocene? A Terrestrial Paleoclimate Record from the Ebro Basin, Spain: Journal of Geology 115, 601–608. doi: 10.1086/519780

18. Hamer, J.M.M.*, Sheldon, N.D., Nichols, G.J., Collinson, M.E., 2007, Late Oligocene – Early Miocene Palaeosols of Distal Fluvial Systems, Ebro Basin, Spain: Palaeogeography, Palaeoclimatology, Palaeoecology 247, 220–235. doi: 10.1016/j.palaeo.2006.10.016


17. Sheldon, N.D., 2006, Teaching Quantitative Skills and Integrative Thinking in the Earth Sciences Using Object-Oriented Models: Planet, v. 17, p. 44–47. doi: 10.11120/plan.2006.00170044

16. Retallack, G.J., Metzger, C.A.*, Jahren, A.H., Greaver, T.*, Smith, R.M.H., Sheldon, N.D., 2006, Middle-Late Permian mass extinction on land: GSA Bulletin 118, 1398–1411. doi: 10.1130/B26011.1

15. Sheldon, N.D., 2006, Precambrian Paleosols and Atmospheric CO2 Levels: Precambrian Research 147, 148–155. doi: 10.1016/j.precamres.2006.02.004

14. Sheldon, N.D., 2006, Quaternary Glacial-Interglacial Climate Cycles in Hawaii: Journal of Geology 114, 367–376. doi: 10.1086/500993

13. Sheldon, N.D., 2006, Abrupt chemical weathering increase across the Permian-Triassic boundary: Palaeogeography, Palaeoclimatology, Palaeoecology 231, 315–321. doi: 10.1016/j.palaeo.2005.09.001

12. Perez-Huerta, A.*, and Sheldon, N.D., 2006. Pennsylvanian Sea Level Cycles, Nutrient Availability, and Brachiopod Community Structure: Palaeogeography, Palaeoclimatology, Palaeoecology 230, 264–279. doi: 10.1016/j.palaeo.2005.07.020

11. Sheldon, N.D., 2006, Using Paleosols of the Picture Gorge Basalt to Reconstruct the Middle Miocene Climatic Optimum: Paleobios, v. 26 (2), p. 27–36.


10. Sheldon, N.D., 2005, Do red beds indicate paleoclimatic conditions?: A Permian case study: Palaeogeography, Palaeoclimatology, Palaeoecology 228, 305–319. doi: 10.1016/j.palaeo.2005.06.009

9. Retallack, G.J., Jahren, H., Sheldon, N.D., Chakrabarti, R.*, Metzger, C.A.*, and Smith, R.M.H., 2005. The Permian-Triassic boundary in Antarctica: Antarctic Science 17, 241–258.doi: 10.1017/S0954102005002658


8. Sheldon, N.D., and Retallack, G.J., 2004, Regional Paleoprecipitation Records from the Late Eocene and Oligocene of North America: Journal of Geology 112 (4), 487-494. doi: 10.1086/421076


7. Sheldon, N.D., 2003, Pedogenesis and Geochemical Alteration of the Picture Gorge Subgroup, Columbia River Basalt, Oregon: GSA Bulletin 115 (11), 1377–1387. doi: 10.1130/B25223.1

6. Retallack, G.J., Sheldon, N.D., Cogoini, M.*, and Elmore, R.D., 2003, Magnetic susceptibility of early Paleozoic and Precambrian paleosols: Palaeogeography, Palaeoclimatology, Palaeoecology 198, 373–380. doi: 10.1016/S0031-0182(03)00479-6

5. Sheldon, N.D., and Retallack, G.J., 2003, Reply to Huggett and Hesselbo Comment on, Low oxygen levels in earliest Triassic soils: Geology 31, e20–e21. doi: 10.1130/0091-7613-31.1.e21


4. Sheldon, N.D., Retallack, G.J., and Tanaka, S., 2002, Geochemical climofunctions from North America soils and application to paleosols across the Eocene-Oligocene boundary in Oregon: Journal of Geology 110 (6), 687–696. doi: 10.1086/342865

3. Sheldon, N.D., and Retallack, G.J., 2002, Low oxygen levels in earliest Triassic soils: Geology 30 (10), 919–922. doi: 10.1130/0091-7613(2002)0302.0.CO;2


2. Sheldon, N.D., and Retallack, G.J., 2001, Equation for compaction of paleosols due to burial: Geology 29 (3), 247–250. doi: 10.1130/0091-7613(2001)0292.0.CO;2

1. Clyde, W.C., Sheldon, N.D., Koch, P.L., Gunnell, G.F., and Bartels, W.S., 2001, Linking the Wasatchian/Bridgerian Boundary to the Cenozoic Global Climate Optimum: New Magnetostratigraphic and Isotopic Results from South Pass, Wyoming: Palaeogeography, Palaeoclimatology, Palaeoecology 167 (1-2), 175–199. doi: 10.1016/S0031-0182(00)00238-8

Other Refereed Publications (2)

Sheldon, N.D., 2008, Red beds, ed. Vivien Gornitz, Encyclopedia of Paleoclimatology and Ancient Environments, Kluwer Academic Publishers, pp. 871-873.

Sheldon, N.D., 2007, Montana – home of the world’s staple foods?: Planet Earth, v. 6, p. 20–21.