Geir Hestmark

• Hestmark, Geir (2023). A Tale of two Moraines and the Discovery of Ice Ages. Geological Society Special Publication. ISSN 0305-8719. 543(1), p. 295–301. doi: 10.1144/SP543-2022-239. Full text in Research Archive Show summary

  Abstract The discovery of Ice Ages is one of the most revolutionary advances ever made in the Earth sciences. In Norway this discovery was made by Danish–Norwegian geoscientist Jens Esmark and his young student Niels Otto Tank, who on a mountain traverse in early September 1823 observed a number of geomorphological features produced by an extant glacier, and compared these to similar features they had previously noted where glaciers today are absent. Seeing a recent moraine pushed up by an extant glacier they suddenly realized that a big ridge of gravel they had earlier seen at sea-level in Southern Norway had to be an ancient moraine, deposited by a big glacier at a time when the climate was substantially colder than today. The brevity of Esmark's account made the precise location of the site of enlightenment remain a mystery for almost two hundred years until it was rediscovered by the author in 2008. This paper describes the crucial site and its lessons.

• Hestmark, Geir (2021). Proposal to conserve the name Umbilicaria spodochroa (lichenized Ascomycota) with a conserved type and with that spelling. Taxon. ISSN 0040-0262. 70(5), p. 1131–1132. doi: 10.1002/tax.12578. Full text in Research Archive
• Hestmark, Geir (2018). Jens Esmarks mountain-glacier traverse 1823 - the key to his discovery of ice ages. Boreas. ISSN 0300-9483. 47(1), p. 1–10. doi: 10.1111/bor.12260. Full text in Research Archive Show summary

  The discovery of Ice Ages is one of the most revolutionary advances made in the Earth sciences. In 1824 Danish‐Norwegian geoscientist Jens Esmark published a paper stating that there was indisputable evidence that Norway and other parts of Europe had previously been covered by enormous glaciers carving out valleys and fjords, in a cold climate caused by changes in the eccentricity of Earth's orbit. Esmark and his travel companion Otto Tank arrived at this insight by analogous reasoning: enigmatic landscape features they observed close to sea level along the Norwegian coast strongly resembled features they observed in the front of a retreating glacier during a mountain traverse in the summer of 1823. Which glacier they observed up close has however remained a mystery, and thus an essential piece of information in the story of this discovery has been missing. Based on previously unknown archive sources, supplemented by field study, I here identify the key locality as the glacier Rauddalsbreen. This is the northernmost outlet glacier from Jostedalsbreen, the largest glacier in mainland Europe. Here the foreland exposed by glacier retreat since the Little Ice Age maximum around AD 1750 contains a rich collection of glacial deposits and erosional forms. The point of enlightenment is more precisely identified to be a specific moraine and its distal sandur at 61°53′26″N, 7°26′43″E. In memory of Esmark's travel companion who possibly was the first to realise the analogy, it is proposed to name this moraine Otto Tank's Moraine, a pendant to the already famous Esmark Moraine at Forsand by the sea.

• Hestmark, Geir (2017). Tracings of the north of Europe: Robert Chambers in search of the Ice Age. Annals of Science. ISSN 0003-3790. 74(4), p. 262–281. doi: 10.1080/00033790.2017.1390154. Full text in Research Archive
• Hestmark, Geir (2017). Lectotypification of Umbilicaria torrefacta (Lightf.) Schrad. The Lichenologist. ISSN 0024-2829. 49(2), p. 167–169. doi: 10.1017/S0024282916000682. Full text in Research Archive
• Hestmark, Geir (2017). Lectotypification of Umbilicaria leiocarpa (Umbilicariaceae). Graphis Scripta. ISSN 0901-7593. 29(1-2), p. 12–17. doi: 10.1017/s0024282914000589. Full text in Research Archive
• Hestmark, Geir; Lutzoni, Francois & Miadlikowska, Jolanta (2016). Photobiont associations in co-occurring umbilicate lichens with contrasting modes of reproduction in coastal Norway. The Lichenologist. ISSN 0024-2829. 48(5), p. 545–557. doi: 10.1017/S0024282916000232. Full text in Research Archive
• Hestmark, Geir (2016). The lichen genus Umbilicaria in Ecuador. Nordic Journal of Botany (NJB). ISSN 0107-055X. 34(3), p. 257–268. doi: 10.1111/njb.00952. Full text in Research Archive
• Hestmark, Geir & Nordli, Øyvind (2016). Jens Esmark’s Christiania (Oslo) meteorological observations 1816-1838: the first long term continuous temperature record from the Norwegian capital homogenized and analysed. Climate of the Past. ISSN 1814-9324. 12(11), p. 2087–2106. doi: 10.5194/cp-12-2087-2016. Full text in Research Archive Show summary

  In 2010 we rediscovered the complete set of meteorological observation protocols made by Jens Esmark (1762–1839) during his years of residence in the Norwegian capital of Oslo (then Christiania). From 1 January 1816 to 25 January 1839, Esmark at his house in Øvre Voldgate in the morning, early afternoon and late evening recorded air temperature with state-of-the-art thermometers. He also noted air pressure, cloud cover, precipitation and wind directions, and experimented with rain gauges and hygrometers. From 1818 to the end of 1838 he twice a month provided weather tables to the official newspaper Den Norske Rigstidende, and thus acquired a semi-official status as the first Norwegian state meteorologist. This paper evaluates the quality of Esmark's temperature observations and presents new metadata, new homogenization and analysis of monthly means. Three significant shifts in the measurement series were detected, and suitable corrections are proposed. The air temperature in Oslo during this period is shown to exhibit a slow rise from 1816 towards 1825, followed by a slighter fall again towards 1838.

• Hestmark, Geir (2015). Umbilicaria aprina New to the Pyrenees. Graphis Scripta. ISSN 0901-7593. 27(1-2), p. 42–45. Full text in Research Archive
• Hestmark, Geir (2015). Lectotypification of Umbilicaria virginis (Umbilicariaceae). The Lichenologist. ISSN 0024-2829. 47(1), p. 77–81. doi: 10.1017/S0024282914000589. Full text in Research Archive
• Nordli, Øyvind; Hestmark, Geir; Benestad, Rasmus & Isaksen, K. (2015). The Oslo temperature series 1837-2012: Homogeneity testing and temperature analysis. International Journal of Climatology. ISSN 0899-8418. 35(12), p. 3486–3504. doi: 10.1002/joc.4223. Full text in Research Archive
• Hestmark, Geir (2014). Lectotypification of the name Umbilicaria nylanderiana (Umbilicariaceae). Taxon. ISSN 0040-0262. 63(4), p. 914–917. doi: 10.12705/634.12. Full text in Research Archive
• Miadlikowska, Jolanta; Kauff, Frank; Högnabba, Filip; Oliver, Jeffrey C.; Molnar, Katalin & Fraker, Emily [Show all 32 contributors for this article] (2014). A multigene phylogenetic synthesis for the class Lecanoromycetes (Ascomycota): 1307 fungi representing 1139 infrageneric taxa, 317 genera and 66 families. Molecular Phylogenetics and Evolution. ISSN 1055-7903. 79(1), p. 132–168. doi: 10.1016/j.ympev.2014.04.003. Full text in Research Archive
• Hestmark, Geir (2013). Comment to lecture On learning from history by Qvigstad, Norges Bank. Norges banks skriftserie. ISSN 0802-7188. 46, p. 57–59. Full text in Research Archive
• Hestmark, Geir (2012). To discover, yes, but to publish...? Jens Esmark, datolite...and thulite. Bergverksmuseets skriftserie. ISSN 0800-1855. 49, p. 45–52. Full text in Research Archive
• Hestmark, Geir (2012). The meaning of 'metamorphic' - Charles & Mary Lyell in Norway, 1837. Norsk Geologisk Tidsskrift. ISSN 0029-196X. 91(4), p. 247–275. Full text in Research Archive
• Hestmark, Geir; Miadlikowska, Jolanta; Kauff, Frank; Fraker, Emily; Molnar, Katalin & Lutzoni, Francois (2011). Single origin and subsequent diversification of central Andean endemic Umbilicaria species. Mycologia. ISSN 0027-5514. 103(1), p. 45–56. doi: 10.3852/10-012. Full text in Research Archive
• Hestmark, Geir (2011). Vitenskap og dannelse. In Astad, Anne-Marie (Eds.), Årbok 2010. Novus Forlag. ISSN 9788270996469. p. 211–232. Full text in Research Archive
• Hestmark, Geir (2011). The meaning of 'metamorphic' - Charles & Mary Lyell in Norway, 1837. Norsk Geologisk Tidsskrift. ISSN 0029-196X. 91(4), p. 247–275. Full text in Research Archive
• Hestmark, Geir (2010). Typification of the Andean taxa of Umbilicaria described by William Nylander. Mycotaxon. ISSN 0093-4666. 111, p. 51–63. Full text in Research Archive
• Jettestuen, Espen; Nermoen, Anders; Hestmark, Geir; Timdal, Einar & Mathiesen, Joachim (2010). Competition on the Rocks: Community Growth and Tessellation. PLOS ONE. 5(9). doi: 10.1371/journal.pone.0012820. Full text in Research Archive Show summary

  Crustose lichen communities on rocks exhibit fascinating spatial mosaics resembling political maps of nations or municipalities. Although the establishment and development of biological populations are important themes in ecology, our understanding of the formation of such patterns on the rocks is still in its infancy. Here, we present a novel model of the concurrent growth, establishment and interaction of lichens. We introduce an inverse technique based on Monte Carlo simulations to test our model on field samples of lichen communities. We derive an expression for the time needed for a community to cover a surface and predict the historical spatial dynamics of field samples. Lichens are frequently used for dating the time of exposure of rocks in glacial deposits, lake retreats or rock falls. We suggest our method as a way to improve the dating.

• Hestmark, Geir (2009). "Her ligger Sneen evig". Da Dovre falt - for Esmarks barometer" ("Here the snow lies eternal" - Jens Esmark's measurement of Snohetta). Historisk tidsskrift. ISSN 0018-263X. 88(2), p. 231–249. Full text in Research Archive
• Hestmark, Geir (2009). New observations and records for Umbilicaria (Umbilicariaceae) in Bolivia. The Bryologist. ISSN 0007-2745. 112(4), p. 833–838. Full text in Research Archive
• Hestmark, Geir (2008). "A primitive country of rocks and people" - R.I. Murchison's Silurian compaign in Norway, 1844. Norsk Geologisk Tidsskrift. ISSN 0029-196X. 88, p. 117–141. Full text in Research Archive
• Sundquist, B; Haapala, I; Hansen, JM; Hestmark, Geir & Steinthorssons, S (2008). History of geology in Norden. Episodes. ISSN 0705-3797. 31. Full text in Research Archive
• Hibbett, DS; Binder, M; Bischoff, JF; Blackwell, M; Cannon, PF & Eriksson, OE [Show all 67 contributors for this article] (2007). A higher-level phylogenetic classification of the Fungi. Mycological Research. ISSN 0953-7562. 111, p. 509–547. doi: 10.1016/j.mycres.2007.03.004. Full text in Research Archive
• Hestmark, Geir; Skogesal, Olav & Skullerud, Øystein (2007). Early recruitment equals long-term relative abundance in an alpine saxicolous lichen guild. Mycologia. ISSN 0027-5514. 99(2), p. 207–214. Full text in Research Archive
• Hestmark, Geir (2007). Typification of Umbilicaria cinereorufescens. Mycotaxon. ISSN 0093-4666. 100, p. 235–240. Full text in Research Archive
• Gregersen, Inger Katharina; Hegseth, Marit Nøst; Hestmark, Geir; Kongsbak, Ruth Helene & Moe, Therese Fosholt (2006). The relationship between thallus mass, surface area and apothecium production in Umbilicaria rigida. Nova Hedwigia: Zeitschrift für Kryptogamenkunde. ISSN 0029-5035. 82. Full text in Research Archive
• Hestmark, Geir (2005). Michael Sars. In Arntzen, Jon Gunnar (Eds.), Bergensere i tusen år. Fra Olav Kyrre til Sissel Kyrkjebø. Kunnskapsforlaget. p. 157–158. Full text in Research Archive
• Hestmark, Geir; Skogesal, Olav & Skullerud, Øystein (2005). Growth, population density and population structure of Cetraria nivalis during 240 years of primary colonization. The Lichenologist. ISSN 0024-2829. 37, p. 535–541. Full text in Research Archive
• Rydgren, Knut; Økland, Rune H. & Hestmark, Geir (2004). Disturbance severity and community resilience in a borealforest. Ecology. ISSN 0012-9658. 85, p. 1906–1915. Full text in Research Archive Show summary

  We studied the resilience of southeastern Norwegian old-growth Picea abies forest floor vegetation to experimental disturbance. Five treatments, differing in depth of removal of vegetation and soil layers and making up a gradient in disturbance severity, and three controls, were replicated 10 times. The experiment was analyzed with respect to the full species composition before and for seven years after treatment. The soil-buried propagule bank and local, environmental conditionswere recorded before treatment. Total cover of vascular plants and bryophytes and lichens increased slowly after treatmentand was still below pre-disturbance levels after seven years. The rate of succession, measured as change in floristic dissimilarity between recordings made in successive years, declined with time for all treatments. The magnitude of vegetationchange was strongly influenced, by disturbance severity. DCAordination revealed a main gradient in species composition from undisturbed forest floor to severely disturbed vegetationthree years after disturbance, while in the fourth year, thedirection of vegetation change turned in the direction of pre-disturbance positions. The turning point represented the maximum abundance of pioneer species (e.g., Luzula pilosa and Pohlia nutans) relative to dominant species before the disturbance (e.g., Dicranum majus and Hylocomium splendens). The return to pre-disturbance positions from the fourth year was, however, slow and will probably take 5-25 more years to be completed if current trends continue. DCA ordination revealed twoadditional, interpretable, gradients in vegetation; one related to pulses of regeneration from the soil-buried propagulebanks the other represented a gradient in pre-disturbance environmental conditions. We demonstrate that one vegetation gradient related to time after disturbance is insufficient to account for the full complexity of revegetation processes following disturbance.

• Hestmark, Geir; Skogesal, Olav & Skullerud, Øystein (2004). Growth, reproduction, and population structure in four alpine lichens during 240 years of primary colonization. Canadian Journal of Botany. ISSN 0008-4026. 82, p. 1356–1362. doi: 10.1139/B04-068. Full text in Research Archive
• Hestmark, Geir; Skogesal, Olav & Skullerud, Øystein (2004). Growth in the alpine saxicolous lichens Allantoparmelia alpicola and Melanelia stygia. Nova Hedwigia: Zeitschrift für Kryptogamenkunde. ISSN 0029-5035. 78(3-4), p. 301–309. doi: 10.1127/0029-5035/2004/0078-03. Full text in Research Archive
• Hestmark, Geir (2004). Kartleggerne. In Drivenes, E.A. & Jølle, Harald Dag (Ed.), Norsk Polarhistorie, II "Vitenskapene". Gyldendal Norsk Forlag A/S. ISSN 9788205326569. p. 6–103, 493-504. Full text in Research Archive
• Rydgren, K.; Økland, Rune Halvorsen & Hestmark, Geir (2004). Disturbance severity and community resilience in a boreal forest. Ecology. ISSN 0012-9658. 85, p. 1906–1915. Full text in Research Archive
• Hestmark, Geir (2003). Narrating the Arctic - A cultural history of Nordic scientific practices. Historisk tidsskrift. ISSN 0018-263X. 82, p. 307–310. Full text in Research Archive
• Hestmark, Geir (2002). Rett og samfunn, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 418–444. Full text in Research Archive
• Hestmark, Geir; Rasmussen, Tarald & Bliksrud, Liv (2002). Posisjoner i det moderne, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 9–22. Full text in Research Archive
• Hestmark, Geir (2002). Materialisme - fosfor til ettertanke, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 70–125. Full text in Research Archive
• Hestmark, Geir (2002). Nytten og nytelsen - positivisme, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 156–183. Full text in Research Archive
• Hestmark, Geir (2002). Darwinisme - optimisme eller pessimisme? Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 126–155. Full text in Research Archive
• Hestmark, Geir (2002). Norsk natur - beskrivelse, bruk, bevaring, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 272–291. Full text in Research Archive
• Hestmark, Geir (2002). Det målbare menneske, Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISSN 9788203224843. p. 330–355. Full text in Research Archive
• Hestmark, Geir (2001). Fridtjof Nansens Fond til Videnskabens Fremme - Grunnleggelsen. Fridtjof Nansen Minneforelesning År 2000. Årbok / Det norske videnskaps-akademi. ISSN 0332-6209. Full text in Research Archive
• Ramstad, Stine & Hestmark, Geir (2001). Population structure and size-dependent reproductive effort in Umbilicaria spodochroa. Mycologia. ISSN 0027-5514. 93, p. 453–458. Full text in Research Archive
• Hestmark, Geir (2000). The ecophysiology of lichen population ecology. Bibliotheca Lichenologica. ISSN 1436-1698. 75, p. 397–404. Full text in Research Archive
• Ramstad, Stine & Hestmark, Geir (2000). Effective neighbourhoods for a saxicolous lichen. Mycological Research. ISSN 0953-7562. 104, p. 198–204. Full text in Research Archive
• Czeczuga, B.; Kilias, H.; Lumbsch, T. & Hestmark, Geir (2000). Carotenoids in the thalli of lichen species from central Europe. Journal of the Hattori Botanical Laboratory. ISSN 0073-0912. 89, p. 299–311. Full text in Research Archive
• Hestmark, Geir (2000). Oeconomia Naturae L. Millennium Essay. Nature. ISSN 0028-0836. 405, p. 19–19. Full text in Research Archive
• Hestmark, Geir (2000). Temptations of the tree. Millennium Essay. Nature. ISSN 0028-0836. 408, p. 911–911. Full text in Research Archive

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• Hestmark, Geir (2020). Lykkeskipet Bergensfjord. Verdenskrig og etterkrigsår 1939-1959. Kagge Forlag AS. ISBN 9788248926191. 588 p. Full text in Research Archive
• Hestmark, Geir (2018). Hva er ØKOLOGI. Universitetsforlaget. ISBN 9788215027968. 156 p. Full text in Research Archive
• Hestmark, Geir (2017). Istidens Oppdager. Jens Esmark, pioneren i Norges fjellverden. Kagge Forlag AS. ISBN 9788248920274. 720 p. Full text in Research Archive
• Hestmark, Geir (2011). Fridtjof Nansen Minneforelesninger 50 år. Novus Forlag. ISBN 9788270996476. 13 p. Full text in Research Archive
• Hestmark, Geir (2011). Fridtjof Nansen og arktisk geologi. Det Norske Videnskaps-Akademi. ISBN 9788270996476. 30 p. Full text in Research Archive
• Hestmark, Geir (2004). Umbilicaria. In Nash, TH, Ryan, BD, Gries, C, Diederich, P. & Bungartz, F. eds.: Lichen Flora of the Greater Sonoran Desert Region. Vol 2. pp. 548-556. University of Arizona. 9 p. Full text in Research Archive
• Bliksrud, Liv; Hestmark, Geir & Rasmussen, Tarald (2002). Vitenskapens utfordringer, 1850 - 1920 (= Norsk idéhistorie bind IV). Aschehoug & Co. ISBN 9788203224843. 478 p. Full text in Research Archive
• Hestmark, Geir (1999). Vitenskap og Nasjon. Waldemar Christopher Brøgger 1851-1905. Aschehoug & Co. ISBN 9788203223914. 890 p. Full text in Research Archive

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• Hestmark, Geir (2023). En ny lesning av landskapet - Jens Esmarks veier til Istiden. GEO. 2023(1), p. 34–39. Full text in Research Archive
• Hestmark, Geir (2023). Jens Esmarks veier til Istiden. geo365.no. Full text in Research Archive
• Hestmark, Geir (2021). Siste livbåt fra et synkende Europa. Full text in Research Archive
• Hestmark, Geir (2019). On the altitudes of von Humboldt. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 116(26), p. 12599–12600. doi: 10.1073/pnas.1907936116. Full text in Research Archive
• Hestmark, Geir (2017). Oppdagelsen av istiden. Aftenposten Historie. ISSN 1894-5775. 2017(9), p. 81–85. Full text in Research Archive
• Hestmark, Geir; Øyvind, Nordli; Benestad, Rasmus & Isaksen, Ketil (2015). Formidabel temperaturauke. Full text in Research Archive
• Hestmark, Geir (2014). Review of T. Krüger: The Discovery of Ice Ages (2013. Isis. ISSN 0021-1753. 105(2), p. 416–417. Full text in Research Archive
• Hestmark, Geir (2014). Christian Frederiks siste erindring om Norge. GEO. 17(3), p. 10–11. Full text in Research Archive
• Hestmark, Geir (2014). Charles Lyells norske lærebokeksempel. GEO. 17(7), p. 72–72. Full text in Research Archive
• Hestmark, Geir (2013). Oppdagelsen av fjellet. Full text in Research Archive
• Hestmark, Geir (2011). Hvem oppdaget larvikitten? Forskningsnytt fra 1700-tallet. GEO. 14(7), p. 32–35. Full text in Research Archive
• Hestmark, Geir (2011). Naturens tankelæser. En biografi om Hans Christian Ørsted. Historisk tidsskrift. ISSN 0018-263X. 90(2), p. 279–282. Full text in Research Archive
• Hestmark, Geir; Miadlikowska, Jolanta; Kauff, Frank; Fraker, Emily; Molnar, Katalin & Lutzoni, Francois (2011). Erratum. Mycologia. ISSN 0027-5514. 103(2), p. 442–443. doi: 10.3852/103.2.442. Full text in Research Archive
• Hestmark, Geir (2010). Vitenskap og dannelse. Full text in Research Archive
• Hestmark, Geir (2010). Jens Esmark's Paths to the Ice Age. Full text in Research Archive
• Hestmark, Geir (2010). Jens Esmark som klimaforsker. Full text in Research Archive
• Hestmark, Geir (2009). Da Dovre falt. (GEO365.no. Nettavisen for geomiljøet - www.geoaktuelt/forskning/dadovrefalt/). GEO. Full text in Research Archive
• Hestmark, Geir (2009). Da Dovre falt. GEO. 12(4), p. 16–17. Full text in Research Archive
• Hestmark, Geir (2009). Sula-konglomeratet. GEO365.no Nettavisen for geomiljøet. http://www.geo365.no/forskning/sula/ 07.12.2009. GEO. Full text in Research Archive
• Hestmark, Geir (2009). Sula-konglomeratet - fra fossilparadis til istidsbevis. GEO. 12(8), p. 32–35. Full text in Research Archive
• Hestmark, Geir (2009). Hva en forsker trenger. Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. Full text in Research Archive
• Hestmark, Geir (2009). Sem Sæland - Store norske leksikon, snl.no, Geir Hestmark, 2009-03-23, http://www.snl.no/.nbl_biografi/Sem_S%C3%A6land/utdypning. Aschehougs og Gyldendals Store Norske Leksikon. Full text in Research Archive
• Hestmark, Geir (2009). Georg Ossian Sars - Store norske leksikon, snl.no, Geir Hestmark, 2009-03-23, http://www.snl.no/.nbl_biografi/G_O_Sars/utdypning. Aschehougs og Gyldendals Store Norske Leksikon. Full text in Research Archive
• Hestmark, Geir (2009). Iacob D. Sømme - Store norske leksikon, snl.no, Geir Hestmark, 2009-03-23, http://www.snl.no/.nbl_biografi/Iacob_D_S%C3%B8mme/utdypning. Aschehougs og Gyldendals Store Norske Leksikon. Full text in Research Archive
• Hestmark, Geir (2009). Michael Sars - Store norske leksikon, snl.no., Geir Hestmark, 2009-03-23, http:///www.snl.no/.nbl_biografi/Michael_Sars/utdypning. Aschehougs og Gyldendals Store Norske Leksikon. Full text in Research Archive
• Hestmark, Geir (2009). Missing links - hvor viktige er de? (www.forskning.no/artikler/2009/mai/221059). [Internet]. forskning.no. Full text in Research Archive
• Hestmark, Geir (2008). Et (fiktivt) intervju med lektor Theodor Kjerulf i anledning opprettelsen av en geologisk undersøkelse. GEO. 11(1), p. 50–52. Full text in Research Archive
• Hestmark, Geir (2007). Innavl ved Universitetet. (Kronikk 23 april 2007). Full text in Research Archive
• Hestmark, Geir (2005). Sæland, Sem. In Arntzen, Jon Gunnar (Eds.), Norsk biografisk leksikon: Sundt-Wikborg. Kunnskapsforlaget. ISSN 9788257310110. p. 64–65. Full text in Research Archive
• Hestmark, Geir (2005). Sømme, Iacob. In Arntzen, Jon Gunnar (Eds.), Norsk biografisk leksikon: Sundt-Wikborg. Kunnskapsforlaget. ISSN 9788257310110. p. 77–78. Full text in Research Archive
• Hestmark, Geir & NRK, TV1 (2005). Tre menn og et glansbilde. [TV]. NRK. Full text in Research Archive
• Hestmark, Geir (2005). Agent og nasjonsbygger s.24-27. [Journal]. Dagsavisen. Full text in Research Archive
• Hestmark, Geir (2004). Sars, Michael. In Arntzen, Jon Gunnar (Eds.), Norsk biografisk leksikon: Sand-Sundquist. Kunnskapsforlaget. ISSN 9788257307349. p. 49–50. Full text in Research Archive
• Hestmark, Geir (2004). Sars, Georg Ossian. In Arntzen, Jon Gunnar (Eds.), Norsk biografisk leksikon: Sand-Sundquist. Kunnskapsforlaget. ISSN 9788257307349. p. 47–49. Full text in Research Archive
• Hestmark, Geir (2003). Da materialismen kom til Norge. [Radio]. P2. Full text in Research Archive
• Hestmark, Geir (2001). Frans Emil Wielgolaski - 70 år. Blyttia : Norsk botanisk forenings tidsskrift. ISSN 0006-5269. 59, p. 138–142. Full text in Research Archive
• Hestmark, Geir (2001). Ernst Haeckel i Bergen, 1869. Bergens Tidende. ISSN 0804-8983. Full text in Research Archive
• Hestmark, Geir (2000). Program om Sonja Kovalevski. [Radio]. NRK-P2. Full text in Research Archive
• Hestmark, Geir (2000). Verdt å vite - Om W.C.Brøgger. [Radio]. NRK-P2. Full text in Research Archive
• Hestmark, Geir (2000). Umbilicaria aprina Nyl. -- an extreme lichen. Norwegian fungus of the month. IMC7 - Web. pages, Dept. of Biology, UiO. p. 1–14. Full text in Research Archive

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