Tikanga Matawhenua hei Whakatau i te Tau o Papatūānuku
Ko te geochronology he peka o te pūtaiao whenua e ako ana i te tau o ngā rauemi whenua me te raupapa o ngā kaupapa i hanga i a Papatūānuku. Mā te geochronology, ka taea e ngā kaipūtaiao te whakautu i ngā pātai matua: te pakeke o Papatūānuku, te wā i hangaia ai ētahi toka, me te whanaketanga o te hītori o te ao i roto i te wā. Ko te whakatau i te pakeke o Papatūānuku ehara i te mea mā te "tatau whakamuri" mai i tētahi kaupapa kotahi, engari mā te whakakotahitanga o ngā tikanga maha e whakakaha ana tetahi i tetahi—ko te nuinga ko te tau radiometric, te stratigraphy, me te hononga kōiwi. I tēnei wā, e whakaaetia whānuitia ana te pakeke o Papatūānuku he tata ki te 4,54 piriona tau, he hua o te whakaae tahi o ngā taunakitanga matawhenua me ngā taunakitanga whetū.
Ngā Kaupapa Taketake o te Geochronology
I te nuinga o te wā, ka wehea ngā tikanga matawhenua ki ngā rōpū matua e rua: te tau ā-tau me te tau tino. Kāore te tau ā-tau e whakarato i te tau i roto i ngā tau, engari e whakatau ana i te raupapa o ngā kaupapa - ko tēhea te pakeke ake, ko tēhea te taitamariki ake. Ko ētahi tauira ko te mātāpono o te taupatupatu (ko ngā paparanga o raro he tawhito ake), te whanaungatanga tapahi (ko te urunga magma e tapahi ana i ngā paparanga tawhito he taitamariki ake), me ngā kore-taurite, e tohu ana i te "wā ngaro" nā te horo, te kore rānei o te whakatakotoranga.
He rerekē, ko te whakatau tau tūturu (ko te whakatau tau tika ake) ka whakarato i tētahi whakatau tata tau i roto i ngā tau, hei tauira "e 250 miriona tau te pakeke o tēnei toka." Ko te tikanga tau pono rawa atu mō ngā tau tino tawhito ko te whakatau tau radiometric, e ahu mai ana i te pirau o ngā huānga radioactive ki ngā huānga tamahine i tētahi tere e taea te matapae.
Ngā Mātāpono o te Tātai Ine Irahiko
Ka whai hua te whakatau ine irahiko nā te mea he pūmau ētahi ngota, ā, ka pirau noa iho ki ētahi atu ngota. Ko te tere o tēnei pirau ka whakaatuhia i roto i te haurua-ora, arā, ko te wā e hiahiatia ana kia huri te haurua o ngā ngota matua hei ngota tamahine. Nā te mea he āhuatanga ā-tinana pumau te haurua-ora i raro i ngā āhuatanga taiao, ka taea te whakamahi i te ōwehenga o ngā huānga matua me ngā huānga tamahine i roto i te kohuke hei tatau i tōna tau mai i te wā e "raka" ana te kohuke i tana pūnaha (katinga), arā, i te wā e mātao ana te kohuke, ā, kāore e ngāwari te neke haere o ngā huānga matua me ngā huānga tamahine ki roto, ki waho hoki.
Heoi, he mea nui kia mārama ko te whakatau i te tau irahiko te tikanga e whakatau ana i te pakeke o te hanganga, te whakamatao rānei o te kohuke, ehara i te mea ko te pakeke o te "toka" anake i roto i tētahi horopaki. Hei tauira, ka taea e ngā toka metamorphic te tohu i te pakeke o te metamorphism, engari he maha ngā wā kei roto i ngā paru he kōhatu kohuke tawhito ake i te wā i whakatakotoria ai.
Tikanga Uranium–Mata (U–Pb): Te Pou o te Whakatau i te Ao Onamata
Ko tētahi o ngā tikanga tino nui mō ngā toka tawhito ko te tikanga Uranium–Lead (U–Pb), e whakamahia ana mō te kohuke zircon (ZrSiO₄). He tino whai hua te zircon nā te mea:
1. Ka taea te whakauru i te ūrāniuma ki roto i tōna hanganga tioata ina hangaia.
2. Ka whakakore i te mata (Pb) i te wā e whakatiotia ana, nō reira ko te Pb i inehia he hua pirau noa iho.
3. Ātete ki te huarere me te hurihanga o te āhua, nō reira ka taea te penapena i ngā "pūkete wā" tawhito rawa.
I roto i te pūnaha U–Pb, e rua ngā mekameka pirau matua: ko U-238 ki Pb-206 me U-235 ki Pb-207. Mā te whakamahi i ngā "karaka" e rua i te wā kotahi, ka taea e tēnei tikanga te tirotiro whakawhiti ā-roto. Ka whakamahia e ngā tātaritanga hou ngā tikanga pēnei i te LA-ICP-MS, te SIMS rānei, e taea ai te ine i ngā tau i te tauine micron, e āhei ai ngā rohe tipu zircon motuhake ki te whakarato mōhiohio mō ngā huihuinga matawhenua e auau ana.
He mea nui te U–Pb hei whakatau i te pakeke o Papatūānuku nā te mea ka taea e ia te whakatau i te pakeke o ngā toka tawhito rawa atu o Papatūānuku, ā, he mea nui ake, ka taea te whakatau i te pakeke o ngā rauemi o waho o te ao pērā i ngā meteorite i hangaia i te Pūnaha Rā tōmua.
Ngā Tikanga Pāhare Pāhare–Argon (K–Ar) me te Argon–Argon (Ar–Ar)
Ka whakamahia e te tikanga Potassium–Argon (K–Ar) te pirau o K-40 ki Ar-40. Nā te mea he hau te argon, kāore e "rongoa" ngāwari ki roto i ngā kohuke wera hou. I te whakamataotanga o te toka, ka tīmata te argon ki te mau i roto i te whatunga kohuke. Nā tēnei ka whai hua te K–Ar mō te whakatau i te wā o ngā toka puia me ngā toka metamorphic.
Ko tētahi momo rerekētanga matatau ake, ko Argon–Argon (Ar–Ar), e ine ana i te ōwehenga isotope argon mā te whakamahi i te hihi niutron, e whakarato ana i te tika ake, ā, e āhei ai te tātari whakamahana-taahiraa. He tino whai hua tēnei tikanga mō te mārama mēnā kua whakamahanahia anōtia tētahi toka e "tautuhi anō" ana i tana karaka irahiko.
Rubidium–Strontium (Rb–Sr) me Samarium–Neodymium (Sm–Nd)
Ka whakamahia e te tikanga Rb–Sr te pirau o Rb-87 ki Sr-87. He maha ngā wā ka whakamahia tēnei tikanga mō ngā toka mura me ngā toka metamorphic, inā koa te huarahi isochron, he tikanga e whakaiti ana i te hiahia mō ngā whakapae mō te hanganga tuatahi o ngā huānga tamahine.
I taua wā, e mōhiotia ana ko Sm–Nd (ka pirau a Sm-147 ki Nd-143) he ātete ake ki ngā huringa metamorphic, ā, he mea whai hua mō te ako i te whanaketanga o te kirinuku me te mantle o Papatūānuku. Haunga te whakarato i ngā tau, ka āwhina hoki te pūnaha Sm–Nd ki te whakamārama i ngā pūtake magma me te hītori rerekētanga o Papatūānuku, nā te mea ka taea e te neodymium te tohu i te hanganga o te kirinuku whenua mai i te mantle.
Te Whakarāpopototanga o te Wā: Te Papa Whenua me ngā Kōhatu Tātai
Ahakoa e whakawhirinaki ana te whakatau i te pakeke o te Ao ki ngā tikanga ine irirangi, me whai anga whakarōpūtanga anō hoki te matawhenua. Ka taea te hono i ngā paparanga toka parataiao puta noa i te ao mā te whakamahi i ngā āhuatanga whakarōpū, ngā tauira whakatakotoranga, me ngā kōiwi tawhito.
Mā ngā kōiwi tātai—ngā kōiwi o ngā rauropi i ora mō te wā poto engari i horapa whānuitia—ka taea te hono i waenga i ngā rohe. Mā tēnei, ka taea e ngā tohunga whenua te hanga i tētahi tauine wā whenua (hei tauira, Jurassic, Cretaceous, Paleogene), kātahi ka "maukati" i taua tauine whanaunga me te maha tuturu o ngā paparanga puia i waenganui i ngā onepū (hei tauira, te pungarehu puia ka taea te whakatau i te tau ki te U–Pb, ki te Ar–Ar rānei).
Me pēhea te whakatau i te tau o te whenua?
Kāore e taea te whakautu i te pātai mō te pakeketanga o Papatūānuku mā roto noa i ngā toka tawhito rawa atu i te mata, nā te mea kei te hangarua tonutia te kiri o Papatūānuku e ngā nekehanga whenua: ka heke te kiri o te moana, ka hurihia te kiri o te whenua, ā, ka hangaia he magma hou. Nō reira, he maha ngā huarahi e whakamahia ana e ngā kaipūtaiao:
1. Ngā toka tawhito rawa atu o te Ao: Kei roto i ētahi craton (ngā wāhi pumau o ngā whenua) ngā toka tino tawhito, pērā i a Kānata, Greenland, Ahitereiria, me Āwherika ki te Tonga. Hei tauira, kua neke atu i te 4 piriona tau te pakeke o ngā kohuke zircon mai i Ahitereiria ki te Hauāuru, e tohu ana i te hanganga wawe o te kirinuku tuatahi.
2. Ngā meteorite me ngā rauemi o te Pūnaha Rā o mua: Nā te mea e kiia ana ko ngā meteorite he toenga o te hanganga o te Pūnaha Rā, ko ō rātou tau he herenga ki te tau o te hanganga o Papatūānuku. Mā te whakatau U–Pb o ngā meteorite (ina koa ko ngā chondrite) ka puta he tau tata ki te 4,56 piriona tau. I hangaia te Papatūānuku i te wā tino wawe, i taua wā anō, nō reira ko tēnei tau te tohutoro matua.
3. Ngā Tauira o te Marama: Ka āwhina hoki ngā toka o te marama mai i ngā misioni Apollo ki te whakatū i tētahi rārangi wā tōmua. Mā te whakataurite i ngā tau o te Marama me te Ao e tautoko te whakaaro i hangaia ngā mea e rua i ngā wāhanga tōmua o te Pūnaha Rā, tae atu ki te pānga nui e whakaarohia ana i hanga ai te Marama.
Mā te whakakotahi i ēnei taunakitanga, ka whakatau te hapori pūtaiao ko te pakeke o te Ao e 4,54 piriona tau pea (me ētahi āwangawanga iti), ehara i te mea i ahu mai i te tauira kotahi, engari i runga i te ōritetanga o ngā pūnaha isotopic maha me ngā momo rauemi maha.
Ngā Wero me te Manatoko
I roto i te mahi, ka pāngia te whakamātautau ine irahiko e ngā wero pēnei i:
– Pūnaha tuwhera: ka taea e ngā huānga matua, ngā huānga tamariki rānei te tomo me te puta nā te huarere, te hurihanga āhua, ngā waiariki rānei.
– Tautuhi Anō: mā te whakamahana anō ka taea te "tautuhi anō" i te karaka isotopic.
– Te poke: mā te ranunga o ngā kohuke tawhito me ngā kohuke taitamariki i roto i te tauira kotahi ka kore e kitea ngā hua.
Nō reira, ko te matawhenua o ēnei rā e whakawhirinaki ana ki te manatoko whakawhiti: mā te whakamahi i ngā kohuke maha, ngā tikanga isotopic maha, me te horopaki matawhenua mārama. Ko te tātaritanga moroiti o ngā zircons, te tikanga isochron, me te whakakotahitanga o ngā raraunga petrological me te stratigraphic ka whakapakari ake i ngā hua o te whakatau tau.
Te Katinga
He mea nui ngā tikanga matawhenua hei mārama ki te pakeketanga me te hītori roa o Papatūānuku. Mā te matawhenua whanaunga ka puta he raupapa o ngā kaupapa, ko te matawhenua ine ia ka puta he tau tika. Mā te pūnaha U–Pb mō te zircon, K–Ar/Ar–Ar mō ngā kohuke puia, me Rb–Sr me Sm–Nd mō ngā toka mura–whakaahua ka puta te turanga mō te whakatau i ngā tau onamata. Ina whakaritea ngā hua o ēnei tikanga ki ngā meteorite me ngā tauira o te marama, ka puta he pikitia ōrite e tata ana ki te 4,54 piriona tau te pakeke o Papatūānuku. Nō reira, ehara te matawhenua i te taputapu noa mō te "ine i te wā," engari he matapihi pūtaiao ki te kōrero mō te whanaketanga tino uaua o te ao, mai i tōna hanganga tuatahi ki ngā āhuatanga i āhei ai te whanaketanga o te ora.
