Yanayin duniyar dusar ƙanƙara

Duniyar dusar ƙanƙara hasashe ce ta geohistorical da ke ba da shawarar cewa a lokacin ɗaya ko fiye na yanayin gidan kankara na duniya, duniyar duniyar ta zama kusan daskarewa ba tare da wani ruwa mai ruwa ko ruwa mai fallasa ga yanayi ba . Mafi yawan lokacin da aka ambata a ilimi na irin wannan shekarun dusar ƙanƙara na duniya an yi imanin ya faru na ɗan lokaci kafin 650 mya a lokacin lokacin Cryogenian, wanda ya haɗa da aƙalla manyan lokutan dusar ƙanƙara guda biyu, glaciations Sturtian da Marinoan .

Masu goyon bayan ra'ayin suna jayayya cewa ya fi bayyana abubuwan da aka adana wanda aka yi imanin cewa ya samo asali ne daga glacial a wurare masu zafi da sauran siffofi masu ban mamaki a cikin rikodin ilimin ƙasa. Masu adawa da ra'ayin suna kalubalantar shaidar ilimin ƙasa don ƙanƙara ta duniya da yiwuwar yanayin ƙasa na kankara ko ƙanƙarar da aka rufe da teku,   kuma suna jaddada wahalar tserewa daga yanayin daskarewa. Tambayoyi da yawa da ba a amsa su ba sun kasance, gami da ko Duniya cikakkiyar "snowball" ce ko "slushball" tare da ƙananan ma'aunin ma'auni na ruwa mai buɗewa (ko budewa a lokacin). An ba da shawarar abubuwan da suka faru na Snowball Earth sun faru ne kafin radiation na kwatsam na multicellular bioforms da aka sani da fashewar Avalon da Cambrian; mafi yawan abubuwan da suka gabata na Snowball na iya haifar da juyin halitta na multicell.

 Tarihi 

 Shaida ta farko game da ƙanƙara ta dā 
Tsawon lokaci kafin a fara gabatar da ra'ayin glaciation na duniya, jerin abubuwan da aka gano sun faru wadanda suka tara shaidu ga glaciations na Precambrian na dā. Na farko daga cikin wadannan binciken an buga shi ne a cikin 1871 ta hanyar J. Thomson, wanda ya sami kayan da aka sake yin gyare-gyare na zamanin d ̄ a (Tillite) a Islay, Scotland. Irin wannan binciken ya biyo baya a Ostiraliya (1884) da Indiya (1887). Wani binciken na huɗu kuma mai ban sha'awa, wanda aka sani da "Reusch's Moraine," Hans Reusch ne ya ba da rahoton a arewacin Norway a cikin 1891. Sauran binciken da yawa sun biyo baya, amma fahimtar su ta sami cikas saboda kin amincewa (a lokacin) da ke cikin nahiyar.

 An gabatar da ƙanƙara ta duniya 
Douglas Mawson, masanin ilimin ƙasa na Australiya kuma mai binciken Antarctic, ya shafe yawancin aikinsa yana nazarin stratigraphy na Neoproterozoic a Kudancin Australia, inda ya gano zurfin yashi mai zurfi. A sakamakon haka, marigayi a cikin aikinsa, ya yi hasashe game da yiwuwar ƙanƙara ta duniya.

 Tabbacin 
An samo asali ne daga ra'ayin dusar ƙanƙara don bayyana shaidar ilimin ƙasa don bayyanar kankara a wurare masu zafi. Dangane da ƙirar, ra'ayi na kankara-albedo zai haifar da kankara mai saurin ci gaba zuwa ma'auni da zarar kankara ta bazu zuwa cikin 25 ° zuwa 30 ° na ma'aunin. Sabili da haka, kasancewar ajiyar kankara a cikin wurare masu zafi yana nuna rufe kankara na duniya.

Saboda haka, abin da ke da mahimmanci ga kimantawa game da ingancin ka'idar, fahimtar amintacce da mahimmancin shaidar da ta haifar da imani cewa kankara ta taɓa kaiwa wurare masu zafi. Wannan shaidar dole ne ta tabbatar da abubuwa uku:

 Cewa gado yana dauke da tsarin sedimentary wanda zai iya zama kawai ta hanyar aikin glacial;
 Cewa gadon ya kasance a cikin wurare masu zafi lokacin da aka ajiye shi.
 Wannan kankara ta kasance mai aiki a wurare daban-daban na duniya a lokaci guda, kuma babu wasu ajiya na wannan shekarun da ke wanzu.

Wannan batu na ƙarshe yana da wuyar tabbatarwa. Kafin Ediacaran, alamun Biostratigraphic da aka saba amfani da su don daidaita duwatsu ba su nan; saboda haka babu wata hanyar tabbatar da cewa duwatsu a wurare daban-daban a duk faɗin duniya an ajiye su a lokaci guda. Mafi kyawun abin da za a iya yi shi ne kimanta shekarun duwatsu ta amfani da kwanan wata na radiometric, wanda ba shi da daidaito zuwa mafi kyawun shekaru miliyan ko haka.

Abubuwa biyu na farko galibi sune tushen jayayya a kan shari'a-da- shari'a. Hakanan ana iya samar da siffofi masu yawa ta hanyar da ba na kankara ba, kuma kimanta kusan latitudes na ƙasa har ma da kwanan nan kamar yadda 200 Ma za a iya cika shi da matsaloli.

 Palaeomagnetism 
An fara gabatar da ra'ayin dusar ƙanƙara na Duniya don bayyana abin da aka ɗauka a matsayin ajiyar glacial kusa da ma'auni. Tun da yake faranti na tectonic suna motsawa sannu a hankali a tsawon lokaci, tabbatar da matsayinsu a wani batu a cikin tarihin duniya ba abu ne mai sauƙi ba. Baya ga la'akari da yadda za'a iya ganewa da wuraren da za su iya haɗuwa tare, latitude inda aka ajiye dutse na iya ƙuntata ta hanyar palaeomagnetism.

Lokacin da duwatsu masu laushi suka samo asali, ma'adanai masu magnetic a cikinsu suna daidaitawa tare da filin magnetic na Duniya. Ta hanyar daidaitattun ma'auni na wannan palaeomagnetism, yana yiwuwa a kiyasta latitude (amma ba longitude ba) inda aka kafa matrix na dutse. Ma'aunin Palaeomagnetic ya nuna cewa an ajiye wasu datti na asalin glacial a cikin rikodin dutsen Neoproterozoic a cikin digiri 10 na ma'auni,  kodayake daidaito na wannan sake ginawa yana cikin tambaya.  Wannan wuri na palaeomagnetic na bayyane glacial sediments (kamar dropstones) an dauki shi don ba da shawarar cewa glaciers sun shimfiɗa daga ƙasa zuwa matakin teku a cikin latitudes na wurare masu zafi a lokacin da aka ajiye sediments. Ba a bayyana ko wannan yana nuna ƙanƙara ta duniya ko kasancewar yankuna masu ƙanƙanta ba, mai yiwuwa a rufe ƙasar, gwamnatocin ƙanƙarar. Wasu ma sun ba da shawarar cewa mafi yawan bayanai ba su hana duk wani ajiyar glacial zuwa cikin 25 ° na ma'auni ba.

 Manazarta