Shekarar kankara

Shekarar kankara lokaci ne mai tsawo na raguwa a cikin zafin jiki na farfajiyar Duniya da yanayi, wanda ke haifar da kasancewar ko fadada kankara na nahiyar da polar da glaciers na alpine. Yanayin duniya yana canzawa tsakanin shekarun kankara, da kuma lokutan greenhouse lokacin da babu kankara a duniya. Duniya a halin yanzu tana cikin zamanin kankara da ake kira Quaternary glaciation .  Kowane mutum na yanayin sanyi a cikin zamanin kankara ana kiransa lokutan glacial (glacials, glaciations, matakan glacial, filayen wasa, filayen, ko kuma a cikin magana, shekarun kankara), da kuma lokutan zafi a cikin zamanin ƙanƙara ana kiransa interglacials ko interstadials.

A cikin ilimin kankara, ana bayyana kalmar zamanin kankara ta hanyar kasancewar manyan kankara a arewa da kudancin hemispheres. Ta hanyar wannan ma'anar, zamanin Holocene na yanzu shine lokacin interglacial na zamanin kankara. Ana sa ran tarin iskar gas mai guba don jinkirta lokacin glacial na gaba.

 Tarihin bincike 
A cikin 1742, Pierre Martel (1706-1767), injiniya da masanin ilimin ƙasa da ke zaune a Geneva, ya ziyarci kwarin Chamonix a cikin Alps na Savoy .  Note: p. 374 Shekaru biyu bayan haka ya wallafa labarin tafiyarsa. Ya ba da rahoton cewa mazaunan wannan kwarin sun danganta warwatsewar duwatsu masu rikitarwa ga kankara, yana cewa sun taɓa faɗaɗa zuwa nesa. Daga baya an bayar da rahoton irin wannan bayani daga wasu yankuna na Alps. A cikin 1815 masassaƙi da mafarauci Jean-Pierre Perraudin (1767-1858) ya bayyana duwatsu marasa daidaituwa a cikin Val de Bagnes a cikin canton na Valais na Switzerland kamar yadda ya faru ne saboda kankara da suka ci gaba. Wani mai yankan katako da ba a san shi ba daga Meiringen a cikin Bernese Oberland ya ba da shawarar irin wannan ra'ayi a cikin tattaunawa tare da masanin ilimin ƙasa na Switzerland-Jamus Jean de Charpentier (1786-1855) a cikin 1834.  An kuma san kwatankwacin bayani daga Val de Ferret a cikin Valais da Seeland a yammacin Switzerland  da kuma aikin kimiyya na Goethe. Goethe, Johann Wolfgang von: Geologische Probleme und Versuch ihrer Auflösung, Mineralogie und Geologie in Goethes Werke, Weimar 1892, , book 73 (WA II, 9), pp. 253, 254. Ana iya samun irin wannan bayani a wasu sassan duniya. Lokacin da masanin halitta na Bavaria Ernst von Bibra (1806-1878) ya ziyarci Andes na Chile a cikin 1849-1850, 'yan asalin sun danganta burbushin burbushin halittu ga tsohon aikin kankara.

 Tabbacin 
Akwai manyan nau'ikan shaidu guda uku game da shekarun kankara: ilimin ƙasa, sinadarai, da paleontological.

Shaidar ilimin ƙasa don shekarun kankara ta zo a cikin nau'o'i daban-daban, gami da tsaftace dutse da ƙuƙwalwa, glacial moraines, drumlins, yanke kwari, da kuma ajiye harsashi ko tillites da glacial erratics. Gishiri na gaba yana karkatar da kuma share shaidar ilimin ƙasa don glaciations na baya, yana mai da wuya a fassara. Bugu da ƙari, wannan shaidar tana da wuyar kwanan wata daidai; ra'ayoyin farko sun ɗauka cewa glacials ba su da tsawo idan aka kwatanta da dogon interglacials. Zuwan sediment da kankara ya bayyana halin da ake ciki na gaskiya: glacials suna da tsawo, interglacials takaice. Ya ɗauki ɗan lokaci don a yi amfani da ka'idar yanzu.

 Manazarta