Articles
Early Access
An overview of the calendar year timelines used in quaternary science and human history, with special reference to sub-annual dating
Publisher's note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
Published: 26 January 2026
6
Views
4
Downloads
Authors
The year 2025 celebrates the 1500th anniversary of the way we count years since and before the incarnation of Christ. The BC/AD timeline is used in natural and human sciences, with conversions to cal BP and b2k timelines, the latter two representing ages before AD 1950 and AD 2000. Though the timelines may seem established, there are more ways than one to count the calendar years, especially “before Christ” and “before present”. If not correctly addressed, the disparities may impair comparisons between sub-annually and annually resolved records available from tree rings and ice cores, in addition to those from historical documents. The offsets between the timelines range from 0.5 to 2.5 years, which may already be detrimental to determining the cause-effect relationships of short-term events such as volcanic eruptions; however, it is possible that the errors may accumulate if different labs and re-users of data repeat the misconceptions. For example, a tree-ring event dated to 1627.5 BC using one timeline might be misassigned to 1626.5 BC or 1625.5 BC using other timelines. Such confusion may arise due to a “year zero” that is missing from the historical timeline, when the AD and BC years are replaced by positive and negative decimal numbers and when the timelines are converted to the Cartesian coordinate system, and/or due to the timelines used for boreal and austral growing seasons. A previously published formula to convert calendar dates to cal BP dates should be replaced by modified formulae tailored to sub-annual dating in this paper. Similar formulae are also provided for converting b2k ages. Developments in the Quaternary dating methods suggest that the number of disciplines topical to this discussion is likely to increase in the near future. It is emphasized that a clear reference to the particular timeline employed must be clarified in every single individual geoscientific/interdisciplinary study.
Downloads
Download data is not yet available.
Citations
Baillie M.G.L., 1995 – A slice through time: Dendrochronology and precision dating. B.T. Batsford, London (UK).
Bateman, M.D., 2015 – The application of luminescence dating in sea-level studies. In: Handbook of Sea-Level Research. Shennan I., Long A.J. & Horton B.P. (eds.). John Wiley & Sons, Chichester, 404-417. DOI: https://doi.org/10.1002/9781118452547.ch27
Brehm N., Christl M., Knowles T.D.J., Casanova E., Evershed R.P., Adolphi F., Muscheler R., Synal H.-A., Mekhaldi F., Paleari C.I., Leuschner H.-H., Bayliss A., Nicolussi K., Pichler T., Schlüchte, C., Pearson C.L., Salzer M.W., Fonti P., Nievergelt D., Hantemirov R., Brown D.M., Usoskin I. & Wacker L., 2022 – Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE. Nature Communications, 13: 1-8. DOI: https://doi.org/10.1038/s41467-022-28804-9
Bronk Ramsey C., 2009 – Bayesian Analysis of Radiocarbon Dates. Radiocarbon, 51: 337-360. DOI: https://doi.org/10.1017/S0033822200033865
Bronk Ramsey C., Adolphi F., Austin W., Bard E., Bayliss A., Blaauw M., Cheng H., Edwards R.L., Friedrich M., Heaton T., Hogg A., Hua Q., Hughen K., Kromer B., Manning S., Muscheler R., Palmer J., Pearson C., Reimer P., Reimer R., Richards D., Scott M., Southon J., Turney C. & Wacker L., 2024 – Development of the Intcal Database. Radiocarbon, 66: 1852–1868. DOI: https://doi.org/10.1017/RDC.2023.53
Büntgen U. & Oppenheimer C, 2020 – The importance of “year zero” in interdisciplinary studies of climate and history. Proceedings of the National Academy of Sciences of the United States of America, 117: 32845–32847. DOI: https://doi.org/10.1073/pnas.2018103117
Butler P.G., Wanamaker A.D., Scourse J.D., Richardson C.A. & Reynolds D.J., 2013 – Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica. Palaeogeography, Palaeoclimatology, Palaeoecology, 373: 141-151. DOI: https://doi.org/10.1016/j.palaeo.2012.01.016
Declercq G., 2002 – Dionysius Exiguus and the Introduction of the Christian Era. Sacris Erudiri, 41: 165–246. DOI: https://doi.org/10.1484/J.SE.2.300491
Duller G.A.T., 2011 – What date is it? Should there be an agreed datum for luminescence ages? Ancient TL, 29: 1–3. DOI: https://doi.org/10.26034/la.atl.2011.442
Fahrni S.M., Southon J., Fuller B.T., Park J., Friedrich M., Muscheler R., Wacker L. & Taylor R.E., 2020 – Single-Year German oak and Californian Bristlecone Pine 14C Data at the Beginning of the Hallstatt Plateau from 856 BC to 626 BC. Radiocarbon, 62: 919–937. DOI: https://doi.org/10.1017/RDC.2020.16
Emiliani, C., 1993 – Calendar reform. Nature 366: 716. DOI: https://doi.org/10.1038/366716b0
Emiliani C, 1995 – Counting time. Nature 373: 278. DOI: https://doi.org/10.1038/373278c0
Flickinger R.C., 1931 – Who Were the Roman Consuls for the Year Zero? The Classical Journal 26: 337-339.
Friedrich R., Kromer B., Wacker L., Olsen J., Remmele S., Lindauer S., Land A. & Pearson C., 2020 – A New Annual 14C Dataset for Calibrating the Thera Eruption. Radiocarbon, 62: 953-961. DOI: https://doi.org/10.1017/RDC.2020.33
Fritts H.C., 1976 –Tree Rings and Climate. Academic Press, New York (NY).
Gibbard P.L. & Head M.J., 2020 – The Quaternary Period. In: Geologic Time Scale 2020. Gradstein F.M., Ogg J.G., Schmitz M.D. & Ogg G.M. (eds.). Elsevier, Volume 2: 1217-1255. DOI: https://doi.org/10.1016/B978-0-12-824360-2.00030-9
Godwin H., 1962 – Half-life of Radiocarbon. Nature, 195: 984. DOI: https://doi.org/10.1038/195984a0
Gould S.J., 2011 – Questioning the millennium. Harvard University Press, Cambridge (MA).
Grün R., 2008 – Editorial. Quaternary Geochronology, 3: 1. DOI: https://doi.org/10.1016/j.quageo.2007.09.001
Holden N.E., Bonardi M.L., De Bievre P., Renne P.R. & Villa I.M., 2011 – IUPAC-IUGS Common Definition and Convention on the Use of the Year as a Derived Unit of Time. Episodes, 34: 39–40. DOI: https://doi.org/10.18814/epiiugs/2011/v34i1/006
Hua Q, Barbetti M, Levchenko VA, D'Arrigo RD, Buckley BM and Smith AM, 2012 – Monsoonal influence on Southern Hemisphere 14CO2. Geophysical Research Letters, 39: 1-5. DOI: https://doi.org/10.1029/2012GL052971
Hua Q., Barbetti M. & Rakowski A.Z., 2013 – Atmospheric Radiocarbon for the Period 1950–2010. Radiocarbon, 55: 2059-2072. DOI: https://doi.org/10.2458/azu_js_rc.v55i2.16177
International Organization for Standardization, 2004 – International Standard ISO 8601. Data elements and interchange formats. Information interchange. Representation of dates and times. 3rd ed. ISO copyright office, Geneva (CH).
Kalliokoski, M., Guðmundsdóttir, E.R., Wastegård, S., Jokinen, S. & Saarinen, T., 2023 – A Holocene tephrochronological framework for Finland. Quaternary Science Reviews, 312: 1-18. DOI: https://doi.org/10.1016/j.quascirev.2023.108173
Kukla, G., 1994 – Counting time. Nature, 372: 124. DOI: https://doi.org/10.1038/372124d0
Lambe S., 2024 – Waste of Time? Why do we use BC/AD – and should we keep them? History Today, 74: 22-24.
Larsen, D.J., Miller, G.H., Geirsdóttir, Á. & Thordarson, T., 2011 – A 3000-year varved record of glacier activity and climate change from the proglacial lake Hvítárvatn, Iceland. Quaternary Science Reviews, 30, 2715-2731. DOI: https://doi.org/10.1016/j.quascirev.2011.05.026
Lund K, 1999 – International standard for denotation of calendar time. Production Planning & Control, 10: 815-817. DOI: https://doi.org/10.1080/095372899232641
Luterbacher J., Werner J.P., Smerdon J.E., Fernandez-Donado L., Gonzalez-Rouco F.J., Barriopedro D., Ljungqvist F.C., Buentgen U., Zorita E., Wagner S., Esper J., Mccarroll D., Toreti A., Frank D., Jungclaus J.H., Barriendos M., Bertolin C., Bothe O., Brazdil R., Camuffo D., Dobrovolny P., Gagen M., Garica-Bustamante E., Ge Q., Gomez-Navarro J.J., Guiot J., Hao Z., Hegerl G.C., Holmgren K., Klimenko V.V., Martin-Chivelet J., Pfister C., Roberts N., Schindler A., Schurer A., Solomina O., Gunten L., Wahl E. Wanner H., Wetter O., Xoplaki E., Yuan N., Zanchettin D., Zhang H & Zerefos C., 2016 – European summer temperatures since Roman times. Environmental Research Letters, 11: 1-12. DOI: https://doi.org/10.1088/1748-9326/11/2/024001
Maczkowski A., Pearson C., Francuz J., Giagkoulis T., Szidat S., Wacker L., Bolliger M., Kotsakis K. & Hafner A., 2024 – Absolute dating of the European Neolithic using the 5259 BC rapid 14C excursion. Nature Communications, 15: 1-12. DOI: https://doi.org/10.1038/s41467-024-48402-1
Martínez G., Martínez G.A. & Owen L.A., 2023 – Human occupation, site formation, and chronostratigraphy of a mid-Holocene archaeological site at the eastern Pampa-Patagonia transition, Argentina. Quaternary Research, 114: 52-68. DOI: https://doi.org/10.1017/qua.2023.8
McConnell J.R., Sigl M., Plunkett G., Burke A., Kim W.M., Raible C.C., Wilson A.I., Manning J.G., Ludlow F., Chellman N.J., Innes H.M., Yang Z., Larsen J.F., Schaefer J.R., Kipfstuhl S., Mojtabavi S., Wilhelms F., Opel T., Meyer H. & Steffensen J.P., 2020 – Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom. Proceedings of the National Academy of Sciences of the United States of America, 117: 15443-15449. DOI: https://doi.org/10.1073/pnas.2002722117
Miyake F., Panyushkina I.P., Jull A.J.T., Adolphi F., Brehm N., Helama S., Kanzawa K., Moriya T., Muscheler R., Nicolussi K., Oinonen M., Salzer M., Takeyama M., Tokanai F. & Wacker L., 2021 – A single-year cosmic ray event at 5410 BCE registered in 14C of tree rings. Geophysical Research Letters, 48: 1-8. DOI: https://doi.org/10.1029/2021GL093419
Noller J.S., Sowers J., Colman S. & Pierce K., 2000 – Introduction to Quaternary geochronology. In: Quaternary Geochronology; Methods and Applications. Noller J.S., Sowers J.M. & Lettis, W.R. (eds.). AGU Reference Shelf, Washington DC, USA, 4: 1-10. DOI: https://doi.org/10.1029/RF004p0001
Pearson C.L., Brewer P.W., Brown D., Heaton T.J., Hodgins G.W.L., Jull A.J.T., Lange T. & Salzer M.W., 2018 – Annual radiocarbon record indicates 16th century BCE date for the Thera eruption. Science Advances, 4: 1-7. DOI: https://doi.org/10.1126/sciadv.aar8241
Pearson C., Salzer M., Wacker L., Brewer P., Sookdeo A. & Kuniholm P., 2020 – Securing timelines in the ancient Mediterranean using multiproxy annual tree-ring data. Proceedings of the National Academy of Sciences of the United States of America, 117: 8410-8415. DOI: https://doi.org/10.1073/pnas.1917445117
Pearson C., Sigl M., Burke A., Davies S., Kurbatov A., Severi M., Cole-Dai J., Innes H., Albert P.G. & Helmick M., 2022 – Geochemical ice-core constraints on the timing and climatic impact of Aniakchak II (1628 BCE) and Thera (Minoan) volcanic eruptions. PNAS Nexus, 1: 1-12. DOI: https://doi.org/10.1093/pnasnexus/pgac048
Randall J, 2000 – Comment on “Which one is correct, 2000 or 2001? How about 1995?” Eos, 81: 532. DOI: https://doi.org/10.1029/EO081i045p00532-02
Rasmussen S.O., Andersen K.K., Svensson A.M., Steffensen J.P., Vinther B.M., Clausen H.B., Siggaard-Andersen M.-L., Johnsen S.J., Larsen L.B., Dahl-Jensen D., Bigler M., Röthlisberger R., Fischer H., Goto-Azuma K., Hansson M.E. & Ruthon U., 2006 – A new Greenland ice core chronology for the last glacial termination. Journal of Geophysical Research, 111: 1-16. DOI: https://doi.org/10.1029/2005JD006079
Rasmussen S.O., Dahl-Jensen D., Fischer H., Fuhrer K., Hansen S.B., Hansson M., Hvidberg C.S., Jonsell U., Kipfstuhl S., Ruth U., Schwander J., Siggaard-Andersen M.-L., Sinnl G., Steffensen J.P., Svensson A.M. & Vinther B.M., 2023 – Ice-core data used for the construction of the Greenland Ice-Core Chronology 2005 and 2021 (GICC05 and GICC21). Earth System Science Data, 15: 3351-3364. DOI: https://doi.org/10.5194/essd-15-3351-2023
Rasmussen S.O., Svensson A.M. & Vinther B.M., 2022 – Greenland Ice-Core Chronology 2005 (GICC05) annual layer depths for various Greenland ice cores [dataset bundled publication]. PANGAEA <https://doi.org/10.1594/PANGAEA.943195> (retrieved in March 3, 2025).
Regev J., Gadot Y., Uziel J., Chalaf O., Shalev Y., Roth H., Shalom N., Szanton N., Bocher E., Pearson C.L., Brown D.M., Mintz E., Regev L. & Boaretto E., 2024 – Radiocarbon chronology of Iron Age Jerusalem reveals calibration offsets and architectural developments. Proceedings of the National Academy of Sciences of the United States of America, 121: 1-12. DOI: https://doi.org/10.1073/pnas.2321024121
Reimer P., Austin W., Bard E., Bayliss A., Blackwell P., Bronk Ramsey C., Butzin M., Cheng H., Edwards R., Friedrich M., Grootes P., Guilderson T., Hajdas I., Heaton T., Hogg A., Hughen K., Kromer B., Manning S., Muscheler R., Palmer J., Pearson C., van der Plicht J., Reimer R., Richards D., Scott E., Southon J., Turney C., Wacker L., Adolphi F., Büntgen U., Capano M., Fahrni S., Fogtmann-Schulz A., Friedrich R., Köhler P., Kudsk S., Miyake F., Olsen J., Reinig F., Sakamoto M., Sookdeo A. & Talamo S., 2020 – The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0-55 kcal BP). Radiocarbon, 62: 725-757. DOI: https://doi.org/10.1017/RDC.2020.41
Reimer P.J., Brown T.A. & Reimer R.W., 2004 – Discussion: Reporting and Calibration of Post-Bomb 14C Data. Radiocarbon, 46: 1299-1304. DOI: https://doi.org/10.1017/S0033822200033154
Reynolds D.J., Richardson C.A., Scourse J.D., Butler P.G., Hollyman P., Román-González A. & Hall I.R., 2017 – Reconstructing North Atlantic marine climate variability using an absolutely-dated sclerochronological network. Palaeogeography, Palaeoclimatology, Palaeoecology, 465B: 333-346. DOI: https://doi.org/10.1016/j.palaeo.2016.08.006
Rose J, 2007 – The use of time units in Quaternary Science Reviews. Quaternary Science Reviews 26: 1193. DOI: https://doi.org/10.1016/j.quascirev.2007.04.002
Sakurai H., Tokanai F., Miyake F., Horiuchi K., Masuda K., Miyahara H., Ohyama M., Sakamoto M., Mitsutani T. & Moriya T., 2020 – Prolonged production of 14C during the ~660 BCE solar proton event from Japanese tree rings. Scientific Reports, 10: 1-7. DOI: https://doi.org/10.1038/s41598-019-57273-2
Sano M., Kimura K., Miyake F., Tokanai F. & Nakatsuka T., 2023 – Two new millennium-long tree-ring oxygen isotope chronologies (2349–1009 BCE and 1412–466 BCE) from Japan. Radiocarbon, 65: 721-732. DOI: https://doi.org/10.1017/RDC.2023.29
Schulman E., 1956 – Dendroclimatic changes in Semiarid America. University of Arizona Press, Tucson (AZ).
Sigl M., Winstrup M., McConnell J.R., Welten K.C., Plunkett G., Ludlow F., Büntgen U., Caffee M., Chellman N., Dahl-Jensen D., Fischer H., Kipfstuhl S., Kostick C., Maselli O.J., Mekhaldi F., Mulvaney R., Muscheler R., Pasteris D.R., Pilcher J.R., Salzer M., Schüpbach S., Steffensen J.P., Vinther B.M. & Woodruff T.E., 2015 – Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523: 543-549. DOI: https://doi.org/10.1038/nature14565
Sinnl G., Winstrup M., Erhardt T., Cook E., Jensen C. M., Svensson A., Vinther B.M., Muscheler R. & Rasmussen, S.O., 2022 – A multi-ice-core, annual-layer-counted Greenland ice-core chronology for the last 3800 years: GICC21. Climate of the Past, 18: 1125-1150. DOI: https://doi.org/10.5194/cp-18-1125-2022
Speer J.H., 2010 – Fundamentals of Tree-ring Research. The University of Arizona Press, Tucson (AZ).
Stange U., 2024 – The Anthropocene as a civil time unit. The Anthropocene Review, 11: 550-569. DOI: https://doi.org/10.1177/20530196231204326
Stavi I., Ragolsky G., Haiman M. & Porat N., 2021 – Ancient to recent-past runoff harvesting agriculture in the hyper-arid Arava Valley: OSL dating and insights. The Holocene, 31: 1047-1054. DOI: https://doi.org/10.1177/0959683621994641
Stuiver M. & Pearson G.W., 1993 – High-precision bidecadal calibration of the radiocarbon time scale, AD 1950-500 BC and 2500-6000 BC. Radiocarbon, 35: 1-23. DOI: https://doi.org/10.1017/S0033822200013783
Uusitalo J., Arppe L., Hackman T., Helama S., Kovaltsov G., Mielikäinen K., Mäkinen H., Nöjd P., Palonen V., Usoskin I. & Oinonen M., 2018 – Solar superstorm of AD 774 recorded subannually by Arctic tree rings. Nature Communications, 9: 1-8. DOI: https://doi.org/10.1038/s41467-018-05883-1
van der Plicht J and Hogg A, 2006 – A note on reporting radiocarbon. Quaternary Geochronology, 1: 237-240. DOI: https://doi.org/10.1016/j.quageo.2006.07.001
Veronis G., 2000a – Which one is correct, 2000 or 2001? How about 1995? Eos, 81: 290. DOI: https://doi.org/10.1029/00EO00216
Veronis G., 2000b – Reply to “Comments on “Which one is correct, 2000 or 2001? How about 1995?” Eos, 81: 532. DOI: https://doi.org/10.1029/EO081i045p00532-03
Walker, M.J.C., 2005 – Quaternary Dating Methods. John Wiley & Sons, Chichester (UK).
Walker M., Head M.J., Berkelhammer M., Björck S., Cheng H., Cwynar L., Fisher D., Gkinis V., Long A., Lowe J., Newnham R., Rasmussen S.O. & Weiss H., 2018 – Formal ratification of the subdivision of the Holocene Series/ Epoch (Quaternary System/Period): Two new Global Boundary Stratotype Sections and Points (GSSPs) and three new stages/ subseries. Episodes, 41: 213-223. DOI: https://doi.org/10.18814/epiiugs/2018/018016
Wilkins G.A., 2000 – The year with a name but without a number. Astronomy & Geophysics, 41: 6.9. DOI: https://doi.org/10.1093/astrog/41.6.6.9-a
Wolff E.W., 2007 – When is the ‘‘present’’. Quaternary Science Reviews, 26: 3023-3024. DOI: https://doi.org/10.1016/j.quascirev.2007.10.008
Winger R.M., 1936 – Zero and the calendar. The Scientific Monthly, 43: 363-367. DOI: https://doi.org/10.2307/2301803
Yang B., Qin C., Wang J., He M., Melvin T.M., Osborn T.J. & Briffa K.R., 2014 – A 3,500-year tree-ring record of annual precipitation on the northeastern Tibetan Plateau. Proceedings of the National Academy of Sciences of the United States of America, 111: 2903-2908. DOI: https://doi.org/10.1073/pnas.1319238111
Yang B., Qin C., Bräuning A., Osborn T.J., Trouet V., Ljungqvist F.C., Esper J., Schneider L., Grießinger J., Büntgen U., Rossi S., Dong G., Yan M., Ning L., Wang J., Wang X., Wang S., Luterbacher J., Cook E.R. & Stenseth N.C., 2021 – Long-term decrease in Asian monsoon rainfall and abrupt climate change events over the past 6,700 years. Proceedings of the National Academy of Sciences of the United States of America, 118: 1-7. DOI: https://doi.org/10.1073/pnas.2102007118
How to Cite
1.
Helama S. An overview of the calendar year timelines used in quaternary science and human history, with special reference to sub-annual dating. Nat Hist Sci [Internet]. 2026 Jan. 26 [cited 2026 Jan. 28];. Available from: https://sisn.pagepress.org/nhs/article/view/919
Copyright (c) 2026 the Author(s)
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.