Possible Impact of the Earth's Magnetic Field on the History Of
Total Page：16
File Type：pdf, Size：1020Kb
Earth and Planetary Science Letters 246 (2006) 17–26 www.elsevier.com/locate/epsl Possible impact of the Earth's magnetic field on the history of ancient civilizations ⁎ Yves Gallet a, , Agnès Genevey b, Maxime Le Goff a, Frédéric Fluteau a,c, Safar Ali Eshraghi d a Equipe de Paléomagnétisme, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris cedex 05, France b Centre de Recherche et de Restauration des Musées de France, UMR CNRS 171, Palais du Louvre, Porte des Lions, 14 quai François Mitterrand, 75001 Paris, France c UFR des Sciences Physiques de la Terre, Université Denis Diderot Paris 7, 2 Place Jussieu, 75251 Paris cedex 05, France d Geological Survey of Iran, Azadi sq., Meraj blvd., PO Box 13185-1494 Tehran, Iran Received 30 November 2005; received in revised form 3 April 2006; accepted 3 April 2006 Available online 19 May 2006 Editor: R.D. van der Hilst Abstract We report new archeointensity results from Iranian and Syrian archeological excavations dated from the second millennium BC. These high-temperature magnetization data were obtained using a laboratory-built triaxial vibrating sample magnetometer. Together with our previously published archeointensity results from Mesopotamia, we constructed a rather detailed geomagnetic field intensity variation curve for this region from 3000 BC to 0 BC. Four potential geomagnetic events (“archeomagnetic jerks”), marked by strong intensity increases, are observed and appear to be synchronous with cooling episodes in the North Atlantic. This temporal coincidence strengthens the recent suggestion that the geomagnetic field influences climate change over multi-decadal time scales, possibly through the modulation of cosmic ray flux interacting with the atmosphere. Moreover, the cooling periods in the North Atlantic coincide with episodes of enhanced aridity in the Middle East, when abrupt societal changes occurred in the eastern Mediterranean and Mesopotamia. Although the coincidences discussed in this paper must be considered with caution, they lead to the possibility that the geomagnetic field impacted the history of ancient civilizations through climatically driven environmental changes, triggering economic, social and political instability. © 2006 Elsevier B.V. All rights reserved. Keywords: Archeomagnetism; climate change; environmental impact; ancient civilizations; Eastern Mediterranean; Mesopotamia 1. Introduction millennia. Relatively numerous archeointensity data were already obtained from this region which permit to Boasting a long and rich cultural past, Mesopotamia know those variations with a quite good time resolution, offers the opportunity to recover the detailed geomag- revealing large and sporadic rapid changes [1–3]. The netic field intensity variations over the past ∼8 detection of rapid geomagnetic field intensity fluctua- tions is of particular interest because Gallet et al. [4] ⁎ Corresponding author. Tel.: +33 1 4427 2432; fax: +33 1 4427 reported a good temporal coincidence, at least over the 7463. past three millennia, between the occurrence of intensity E-mail address: [email protected] (Y. Gallet). maxima in Western Europe and multi-decadal-scale 0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2006.04.001 18 Y. Gallet et al. / Earth and Planetary Science Letters 246 (2006) 17–26 cooling events, for instance, during the Little Ice Age millennia that were correlated with climatic cooling [5–8]. Such a coincidence suggests a link between both events documented in Western Europe from natural and phenomena. St-Onge et al. [9] put forward a similar historical data [4,6–8]. Taking advantage of previously inference by studying the paleointensity of Holocene reported archeointensity data from Mesopotamia (Syria) sediments from the St. Laurence estuary (Canada). They [2,3], together with new results from Iranian and Syrian proposed that geomagnetic variation may control the archeological excavations presented in this paper, we millennial and perhaps some centennial-scale fluctua- explore whether additional archeomagnetic jerks poten- tions in the production of cosmogenic isotopes. Up to tially occurred during the third and the second millennia now, the latter fluctuations were thought to be caused by BC that would be coincident with both climatic long-term solar variability, and in fact, they were used as variations and cultural changes in the eastern Mediter- a proxy for characterizing this variability and deriving ranean and Mesopotamia. the Holocene climatic changes (e.g., [10,11]). On the other hand, the geomagnetic dipole moment was 2. Acquisition of new archeointensity results from assumed to have varied smoothly during the Holocene Iran and Syria (e.g., [12]), which is contradicted by recent paleomag- netic and archeomagnetic data and field modeling We analyzed 13 groups of baked brick fragments [2,9,13–15]. Altogether, these results support the idea collected from three Iranian and two Syrian arche- that geomagnetic field secular variation may trigger ological sites. The Iranian excavations (Haft Tepe, dynamical processes in the atmosphere, such as the rate Chogha Zanbil and Susa), well described in Potts [24], of cosmogenic nuclide production and climatic fluctua- are located in the Mesopotamian alluvial plain in tions, over centennial time scales. We presently know southwestern Iran (Khuzistan province; Fig. 1). Four little about the mechanism that could link the geomag- archeomagnetic sites were collected from the tomb- netic field of internal origin to climate change. An temple complex at Haft Tepe. Fragments were taken appealing, but not yet demonstrated scenario is that from two pavements (IR04, IR07) and two tombs (IR05 variations in field morphology (sporadic dipole axis and IR06) dated from the Middle Elamite I period motion toward lower latitudes or non-dipole features) (∼1500–1400 BC according to the Middle Chronology could modulate the cosmic ray flux interacting with the framework; e.g., [25]). Five archeomagnetic sites were atmosphere, altering cloud nucleation, and thus the collected from Chogha Zanbil, particularly remarkable Earth's radiation budget [4,9,16,17]. for its impressive and well preserved ziggurat. Groups If confirmed, the above relationship would give the of fragments were taken from the ziggurat itself (IR02, possibility that the geomagnetic field, because of its IR03), from two vaulted tombs located in the palace impact on climate, influenced the trajectory of ancient hypogeum (IR01, IR09) and from a water reservoir civilizations. Cultural responses to Holocene climatic (IR08). As discussed in Potts [24], all the structures variations have been the subject of several studies, were built by King Untash-Napirisha during the Middle leading for instance to the claim that the collapse of the Elamite II period (∼1350–1300 BC). Two other Akkadian empire at ∼2150 BC was provoked by a archeomagnetic sites were collected from Susa, where drought, evidence for which was found in Oman Gulf we sampled two pavements dated from the Achemenid sediments [18,19], or that the Bronze Age/Iron Age period, one at the Darius royal residence (522–486 BC; transition in Europe was triggered by a climatic IR10) and the other at the Shaur palace built under King degradation detected in raised-bog deposits from The Artaxerxes II (404–358 BC; IR11). Netherlands [20]. Other examples of societal collapses Two additional archeomagnetic sites were collected caused by climatically induced environmental changes from the old cities of Mari and Terqa located along the were also suggested in Mesoamerica, in particular for middle course of the Euphrates river in eastern Syria explaining the end of the Classic Maya empire around (Fig. 1). Lot25 from Mari consists of fragments from a the end of the first millennium AD [21]. water conduit found in a building constructed inside the Our attention was originally attracted by a special Great Royal Palace (City 3 of Mari) during the reign of geomagnetic feature characterized by a strong intensity Shamsi Adad I, shortly before the destruction of the city maximum synchronous with abrupt directional changes by the Babylonian troops of King Hammurabi observed at ∼800 BC, at the time of the Bronze Age/ (∼1750 BC in the middle chronology) [26]. Note that Iron Age transition [4,13,17,22,23]. Other similar this archeomagnetic site is slightly younger than the two geomagnetic features, called “archeomagnetic jerks” sites MR11 and MR08, also dated from the Amorite by Gallet et al. [13], were detected over the past three Dynasty (end of City 3 of Mari), which were previously Y. Gallet et al. / Earth and Planetary Science Letters 246 (2006) 17–26 19 Fig. 1. Location map of the different archeological excavations in Iran and Syria where the groups of baked brick fragments analyzed in this paper have been collected. analyzed by Genevey et al. [2] and Gallet and Le Goff here these criteria which were deduced from the [3]. Finally, in Terqa, we sampled several fragments analysis of thermally stabilized samples possessing from a water conduit dated from the Khana period varying pseudo-ancient NRM acquired in known (∼1750–1500 BC; Lot26) [27]. laboratory-field and temperature conditions: Archeointensity determinations were derived using the experimental procedure described in Le Goff and i) The magnetization must be univectorial through Gallet [28] (and references herein), which involves the entire temperature interval considered for continuous high-temperature and