Nzira yeGeochronology muKuziva Zera rePasi
Geochronology ibazi resainzi yepasi rinoongorora nguva yezvinhu zve geological uye kutevedzana kwezviitiko zvakaumba Nyika. Kuburikidza ne geochronology, masayendisiti anogona kupindura mibvunzo inokosha: kuti Nyika ine makore mangani, kuti mamwe matombo akaumbwa riini, uye kuti nhoroondo yepasi inoenderera mberi sei nekufamba kwenguva. Kuziva zera reNyika hakuitwi nekungo "verenga uchidzokera kumashure" kubva pachiitiko chimwe chete, asi kuburikidza nekusanganiswa kwenzira dzakawanda dzinosimbisana - kunyanya radiometric dating, stratigraphy, uye fossil correlation. Parizvino, zera reNyika rinogamuchirwa zvakanyanya kuti rinenge makore mabhiriyoni 4,54, zvichikonzerwa nekubvumirana kwehumbowo hwe geochemical ne nyeredzi.
Nheyo dzeGeochronology
Kazhinji, nzira dze geochronological dzakakamurwa kuita mapoka maviri makuru: relative dating uye absolute dating. Relative dating haipe zera mumakore, asi inosarudza kutevedzana kwezviitiko—kuti ndechipi chakakura uye kuti ndechipi chiri chidiki. Mienzaniso inosanganisira musimboti we superposition (lower sedimentary layers anowanzova ekare), truncation relationship (magma intrusion inocheka nepakati pema layers ekare idiki), uye unconformities, izvo zvinoratidza "kurasika kwenguva" nekuda kwekukukurwa kana kushaya deposition.
Kusiyana neizvi, kufambidzana kwakakwana (kunyanya kufambidzana kwenhamba) kunopa fungidziro yezera muhuwandu, semuenzaniso "dombo iri rine makore mamiriyoni mazana maviri nemakumi mashanu ekuberekwa." Nzira yakavimbika yekuverenga nhamba yekukwegura kwakanyanya ndeyekufananidza nhamba ne radiometric, zvichibva pakuora kwezvinhu zvine radioactive kuita zvinhu zvemwanasikana nekukurumidza kunofungidzirwa.
Nheyo dzeRadiometric Dating
Kuverenga nguva kweRadiometric kunoshanda nekuti mamwe maatomu haana kugadzikana uye anoora zvechisikigo kuita mamwe maatomu. Mwero wekuora uku unoratidzwa maererano nehafu yehupenyu, inova nguva inodiwa kuti hafu yemaatomu emubereki ive maatomu emwanasikana. Nekuti hafu yehupenyu chinhu chinoramba chiripo pasi pemamiriro echisikigo, chiyero chezvinhu zvemubereki nemwanasikana mumineral chinogona kushandiswa kuverenga makore acho kubva panguva iyo mineral "inovhara" system yayo (kuvhara), ndiko kuti, apo mineral inotonhora uye zvinhu zvemubereki nemwanasikana hazvichafambi nekubuda zviri nyore.
Zvisinei, zvakakosha kunzwisisa kuti kuverengwa kwenguva pfupi (radiometric dating) kunowanzo ratidza makore ekuumbwa kwezvicherwa kana kutonhorera, kwete makore e "dombo" chete mune chero mamiriro ezvinhu. Semuenzaniso, matombo akachinja chimiro anogona kuratidza makore ekuchinja chimiro, nepo marara achiwanzova nemaminerari akare kupfuura nguva yawo yekuiswa.
Nzira yeUranium–Lead (U–Pb): Kusarudza kweMbiru yeNguva Yekare
Imwe yenzira dzakakosha dzekushandisa matombo ekare inzira yeUranium–Lead (U–Pb), inowanzo shandiswa pamineral zircon (ZrSiO₄). Zircon inobatsira zvikuru nekuti:
1. Inokwanisa kuisa uranium muchimiro chayo chekristaro kana yaumbwa.
2. Inoramba lead (Pb) panguva yekuumbwa kwekristall, zvekuti Pb inoyerwa inowanzo kuve mugumisiro wekuora.
3. Haina kukanganiswa nemamiriro ekunze uye shanduko, saka inogona kuchengetedza "zvinyorwa zvenguva" zvekare.
Muhurongwa hweU–Pb, kune nzira mbiri huru dzekuora: U-238 kusvika kuPb-206 uye U-235 kusvika kuPb-207. Ne "mawachi" maviri panguva imwe chete, nzira iyi inobvumira kuongorora mukati. Ongororo dzemazuva ano dzinoshandisa matekiniki akadai seLA-ICP-MS kana SIMS, ayo anogona kuyera makore pachikero che micron, zvichibvumira nzvimbo dzakasiyana dzekukura kwe zircon kupa ruzivo nezvezviitiko zve geological zvinodzokororwa.
U–Pb inokosha pakufungidzira makore ePasi nekuti inogona kuratidza kuti matombo ekare kupfuura mamwe ose ari panyika ndeapi uye, chinonyanya kukosha, inoratidza kuti zvinhu zviri kunze kwenyika zvakaita semameteorite akaumbwa muSolar System yekutanga.
Nzira dzePotassium–Argon (K–Ar) uye Argon–Argon (Ar–Ar)
Nzira yePotassium–Argon (K–Ar) inoshandisa kuora kweK-40 kuenda kuAr-40. Nekuti argon igesi, haichengetwi zviri nyore muzvicherwa zvinopisa, zvitsva. Dombo parinotonhora, argon inotanga kubatwa mulattice yezvicherwa. Izvi zvinoita kuti K–Ar ibatsire pakuwana nguva yematombo emakomo anoputika uye akachinja chimiro.
Imwe nzira yakaoma zvikuru, Argon–Argon (Ar–Ar), inoyera chiyero cheargon isotope ichishandisa neutron irradiation, kazhinji ichipa kunyatsojeka uye ichibvumira ongororo yekupisa-nhanho. Iyi nzira inobatsira zvikuru pakunzwisisa kana dombo rakambodziiswazve izvo "zvinodzoreredza" wachi yaro yeradiometric.
Rubidium–Strontium (Rb–Sr) uye Samarium–Neodymium (Sm–Nd)
Nzira yeRb–Sr inoshandisa kuora kweRb-87 kuenda kuSr-87. Iyi nzira inowanzoshandiswa pamatombo eigneous uye metamorphic, kunyanya nemaitiro eisochron, nzira inoderedza kudiwa kwekufungidzira nezvekuumbwa kwekutanga kwezvinhu zvemwanasikana.
Panguva iyi, Sm–Nd (Sm-147 kuora kusvika kuNd-143) inozivikanwa kuti inodzivirira shanduko dzekuchinja kwezvinhu, zvichiita kuti ibatsire pakudzidza kushanduka kweganda repasi neganda repasi. Pamusoro pekupa nguva, sisitimu yeSm–Nd inobatsirawo kududzira manyuko emagma uye nhoroondo yekusiyana kwepasi, sezvo neodymium inogona kuva chiratidzo chekuumbwa kweganda repasi kubva muganda repasi.
Kufambidzana Kwemhuri: Stratigraphy uye Index Fossils
Kunyange zvazvo kuziva zera rePasi kuchinyanya kushandisa nzira dze radiometric, geochronology inodawo stratigraphic framework. Matombo e sedimentary pasi rose anogona kusanganiswa uchishandisa lithological characteristics, depositional patterns, uye fossils.
Zvisaririra zvemafossil—zvisaririra zvezvipenyu zvakararama kwenguva pfupi asi zvakapararira zvakanyanya—zvinobvumira hukama pakati penzvimbo. Nenzira iyi, nyanzvi dzezvemafossil dzinogona kugadzira chiyero chenguva chezvemafossil (semuenzaniso, Jurassic, Cretaceous, Paleogene), dzobva "dzavhara" chiyero ichocho chine huwandu hwakakwana hwezvikamu zvemakomo anoputika zvakabatana pakati pemadota (semuenzaniso, dota remakomo rinogovaniswa neU–Pb kana Ar–Ar).
Zera rePasi Rinotemerwa Sei?
Mubvunzo wezera reNyika haugone kupindurwa chete kubva pamatombo ekare ari pamusoro, nekuti goko rePasi riri kugara richidzokororwazve ne plate tectonics: goko regungwa rinobviswa, goko repasi rinoshanduka, uye magma itsva inoumbwa. Saka, masayendisiti anoshandisa nzira dzakasiyana-siyana:
1. Matombo ekare kwazvo pasi pano: Matombo ekare zvikuru anowanikwa mumacraton akati wandei (nzvimbo dzakagadzikana dzemakondinendi), akadai seCanada, Greenland, Australia, neSouth Africa. Zvicherwa zveZircon zvinobva kuWestern Australia, semuenzaniso, zvakanzi zvine makore anopfuura mabhiriyoni mana ekuberekwa, zvichiratidza kuti goko rekutanga rakaumbwa kare kare.
2. Mameteorite nezvinhu zvepakutanga zveSolar System: Nekuti mameteorite anoonekwa sezvisaririra zvekuumbwa kweSolar System, makore awo anopa muganho pazera rekuumbwa kweNyika. Kuwanikwa kweU–Pb kwemameteorite (kunyanya machondrite) kunoburitsa chiverengero chemakore angangoita mabhiriyoni 4,56. Nyika yakaumbwa kare kare, munguva imwe chete iyi, saka chiverengero ichi ndicho chinonyanya kutaurwa nezvacho.
3. Mienzaniso yeMwedzi: Matombo emwedzi anobva kumabasa eApollo anobatsirawo pakugadzira nguva yekutanga. Kuenzanisa mazera eMwedzi nePasi kunotsigira pfungwa yekuti zvese zvakaumbwa mumatanho ekutanga eSolar System, kusanganisira chiitiko chikuru chekudonha kwemhepo chinofungidzirwa kuti chakaumba Mwedzi.
Kubatanidza humbowo uhwu, vesainzi vanogumisa kuti Pasi rine makore angangoita mabhiriyoni 4,54 (nekusaziva kudiki), kwete zvichibva pamuenzaniso mumwe chete, asi pane kuenderana kwemasisitimu akawanda eisotopic nemhando dzakasiyana dzezvinhu.
Matambudziko uye Kusimbiswa
Muchokwadi, kufambidzana kwemunhu ne radiometric kunosangana nematambudziko akadai se:
- Sisitimu yakavhurika: zvinhu zvemubereki kana zvemwana zvinogona kupinda nekubuda nekuda kwemamiriro ekunze, shanduko yemamiriro ekunze, kana mvura inopisa.
- Kugadzirisazve: kudziyisazve kunogona "kugadzirisazve" wachi ye isotopic.
– Kusvibiswa: musanganiswa wezvicherwa zvekare nezvidiki mumuenzaniso mumwe chete unogona kuvharidzira mhedzisiro.
Saka, geochronology yemazuva ano inoshandisa kubatanidza zvinhu: kushandisa zvicherwa zvakawanda, nzira dzakasiyana-siyana dze isotopic, uye mamiriro akajeka e geology. Kuongororwa kwe micro-analysis ye zircons, nzira ye isochron, uye musanganiswa we data re petrological ne stratigraphic zvinowedzera kusimbisa mhedzisiro yekutara nguva.
Penutup
Nzira dzeGeochronological dzakakosha pakunzwisisa zera reNyika nenhoroondo yayo refu. Kuverenga nguva yemunhu kunopa kutevedzana kwezviitiko, nepo kuverenga nguva yeradiometric kunopa zera chairo. Sisitimu yeU–Pb yezircon, K–Ar/Ar–Ar yezvicherwa zvemakomo, uye Rb–Sr neSm–Nd yematombo eigneous–metamorphic inopa hwaro hwekuziva zera rekare. Kana mhedzisiro yenzira idzi ikaenzaniswa nemameteorites nemasampuli emwedzi, mufananidzo wakafanana unobuda wekuti Nyika ine makore angangoita mabhiriyoni 4,54. Saka, geochronology haisi chishandiso che "kuyera nguva," asi hwindo resainzi munyaya yekushanduka-shanduka kwakaoma kwazvo kwepasi, kubva pakutanga kwayo kusvika kumamiriro ezvinhu akabvumira hupenyu kukura.
