Iziqhushumbisi Eziphakathi KweePlanethi
Xa ujonga esibhakabhakeni ebusuku, sibonakala sizolile. Inkwekwezi ziyakhanya kwisibhakabhaka esimnyama kwaye kuthe nkcwe akukho enye into phezulu. Kodwa eneneni akunjalo. Umhlaba uhlala uzele zizinto, uninzi lwazo lusuka kwi asteroid belt ephakathi kwe Mars kunye ne Jupiter. Olu hlaselo alupheli, nangona kucingelwa ukuba inani leziqhushumbisi phakathi kweeplanethi lehlile xa kuthelekiswa ngethuba umhlaba wawuqaleka, kuqikelelwa ukuba iitoni ezingama 30 000 zemvuthuluka esuka/ephakathi kwezinye iiplanethi isangena kumoya (atmosphere) wethu minyaka le.Uninzi lwale mvuthuluka neengququ ziyatsha njengoba zibetheka kwi atmosphere, zitsha ziphele tuu ngenxa yesantya somoya. Ukukhanya okugqamileyo okukhutshwa zezimvuthuluka kuzenza zivele njenge meteors okanye iinkwekwezi ezidubulayo (shooting stars). Ukuba imeteor inkulu ngokwaneleyo, ingxenye yayo ingakwazi ukusinda emlilweni ize iwele emhlabeni njenge meteorite. Ukuba ubusazi, eyona meteorite inkulu eyakhe yafunywana ukuzothi gaa ngoku yi Hoba meteorite, neyafunyanwa ngomnyaka ka 1920.
Yabetheka emhlabeni kufuphi nase Grootfontein, kumantla elizwe lase Namibia, kwiminyaka engapha kwama 80 000 eyadlulayo. Kwaye ayikasuswa kulondawo kunanamhla oku. iHoba yingqekembe enkulu ye ayoni kunye ne nickel emeta phantse iimitha ezintathu ububanzi kunye nemitha enye ubude.
Ukuntlitheka Okunamandla
Kodwa kungathini ukuba into enkulu kakhulu ingeza imbonzeleka emhlabeni? Kungenzeka ntoni ukuba ibolide enobubanzi obuli 10 okanye mhlambi obuli 100 lee khilomitha ingazokuntlitheka emhlabeni? Uphando ngeziganeko zontlitheko ezadlulayo azizobi mfanekiso mhla kwaphela.Iziganeko zokuntlitheka okukhulu zikhangeleka zinokonakalisa, hayi lendayo ziwele kuyo kuphela, kodwa iplanethi yonke iphela. Iinkunzi zenyikima, iitsunami, kunye nezikhukula zentaba-mlilo ezidalwe loluntlitheko zingagubungela zitshabalalise kwabomi phuphilayo kulomhlaba. Ngapha koko, uthuli kunye neemvuthululuka ephaphathekele emoyeni/atmosphere zingathintela ukukhanya kwelanga, le planethi ibenobona busika babukhe baqatsela obuhlale iinyanga okanye iminyaka eminintsi. Ngamafutshane, kukholelwa ukuba iziganeko zontlitheko zingalitshabalalisa ihlabathi.
Ukutshabalala
Ukutshabalala okanye ukuphela nya yinto edaliweyo ngokuya ihlabathi likhula. Kwiminyaka engapha kwee bhiliyoni, iindidi ngeendidi zendalo zatshabalala ngenxa yokutshintsha kwemo yezulu, iingozi zendalo kunye nokhuphiswano kunye nezinye iindidi zendalo. Oku kubonwa njengokutshabalala okuqhelekileyo (okanye background) kwaye kusaqhubeka nanamhla oku-Kuncediswa ke nangabantu njengokuba beyichuba iplanethi.Kuqikelelwa ukuba phantsi kwemo eziqhelekileyo, phakathi kwesibini ukuya kwisihlani samaqela ezilwanyana okanye izityalo ezikwiintsapho ezinye ziyatshabalala rhoqo emva kweminyaka esi sigidi. Ukuba kungakho ungcoliseko oluthe kratya esi sibalo singenyuka.
Noxa kunjalo, ushicilelo lwe fosili lubonakalisa ukuba, ngamaxesha athile mandulo, kwabakho ukutshabalala kwendalo okuninzi, nalapho ipesentegi enkulu yobomi obuseMhlabeni yanyamalala ngesiquphe. Oku ke kuye kubizwe nge boundary events kwaye ubungqina bazo bubonakala ekupheleni kwamatye kunye nee fosili, nalapho intlobo ethile yobomi ikhawuleza ingenelwe yenye endaweni yayo.
Ezi boundary events zivamise ukubonakala kumatye olekeneyo akutsha nje, kwii ndawo ezahlukeneyo kwiplanethi yonke jikelele.
Ukutshabalala Kwesininzi
Kuba sixhomekeke kushicilelo lwe fosili ukuze sibone ezi boundaries,ukuqhubeka kokutshabalala kwesininzi kubonakala kuphela emva kokwanda kobomi ngethuba le Cambrian, malunga nama 550 ezigidi zeminyaka eyadlulayo (Ma). Ukusukela ngoko, sele kubekho ukutshabalala kwesininzi izihlandlo ezintlanu: I-End-Ordovician transition (444 Ma: 84% ilahleko yendalo), iLate Devonian (360 Ma: 79% ilahleko yendalo), iEnd-Permian (250 Ma, 95% ilahleko yendalo – okona kutshabalala kwesininzi kwakhe kwabakubi kule planethi), End-Triassic (200 Ma, 79% ilahleko yendalo) kunye ne End-Cretaceous (65 Ma, 70% ilahleko yendalo).Abanye abaphandi balemihla, babanga elokuba kungokunje sijongene nokunye ukutshabalala kwendalo ngesininzi,ngokoshicilelo kokona kwakhe kwakhawuleza. Kubaxwa kakhulu nakukuphatha kwethu gadalala kwendalo esingqongileyo, esi siganeko soku kutshabalala kubizwa nge Holocene extinction kungathetha ukuba isiqingatha sobomi obusemhlabeni singafa kwisithuba seminyaka eli 100 elandelayo ( ngokwengxelo ka sosayensi ongenathemba).
Phela Nya!
Izizathu zoku kutshabalala kwesininzi kunzima ukuzichana ncam. Inye kuphela, (iEnd-Cretaceous, okanye iK-T Boundary) yona ke kuqinisekiwe ukuba kwabangelwa sisiganeko sokuntlitheka. Ezinye akukho siqiniseko sokuba zazibangelwa yintoni, kuba kungekho zintsalela okanye matye antama untlitheko okanye imbangela yoku kutshabalala. Ngaphandle kontlitheko, izizathu ezikrokrelwayo ziquka ezi: utshintsho lwemozulu (olufana namaxesha emikhenkce/Ice age ngelamaNgesi), izizumbulu zentaba mlilo (nezikhupha ityhefu emoyeni), gamma-ray bursts (nezigcada kwanto iphilayo phezu komhlaba) kunye ne plate tectonics (nezinothi zidibanise amazwekazi, ze kudibane iindidi ezahlukeneyo zobomi ebekungafanelanga ukuba ziyadibana, oku kungadala ubomi obutsha ngesiquphe). Kukholeleka ekubeni ayisiyonto inofane yenzeke ukuba zonke ezi ziganeko zingonongekehli zingade zidale ukutshabalala kwesininzi. Kodwa ke, umxube wezinto ezithile lolona qikelelo kukholeleka ukuba lungakwenza oku.Uphando lubonise ukuba ukutshabalala kobomi bendalo ngesininzi kwenzeka ngemijikelo, mhlawumbu kubekanye emva kweminyaka engama 30 ukuya kuma 60 ezigidi. Kwaye kufuneka kuqatshelwe ukuba, ngenxa yokuba singenabungqina buphathekayo beziganeko zokutshabala kwesininzi phambi kwe 500 Ma, akuthethi ukuba azange kwenzeke.
Phambi kwethuba ke Cambrian, ubomi babungekaphucuki kangako. Kwakukho izidalwa ezifana nee ntsholongwane, brachiopods kunye ne trilobites. Ezi zinambuzane zincinane azishiyi mizila mingako ngasemva, ngoko ke amanani azo kunzima ukuwaqikelela. Ngaphezulu koko anqabile amatye asuka kwiminyaka engama 600 ezigidi, kuba evamise ukugubeka kwi
tectonic process. Oku kususa kwabungqina be boundary layers nezinokuntama iziganeko eziyingozi zehlabathi. Ngoko ke, ukuba babukhona ubomi eMhlabeni ngethuba lontlitheko lwe Vredefort, makube baye batshabalala baphela nya!
Translated by Zizipho Silwana