Birashoboka ko umwaka umwe ari igihe kirekire kuri wowe, kuko imyumvire yawe ku gihe iterwa nicyo wakigereranyije nacyo.
Iyo ugereranyije n’ibyo wanyuzemo cyangwa waciyemo mu buzima bwawe, usanga mu by’ukuri umwaka umwe ari muremure! Gusa iyo uwugereranyije n’amateka y’ibihugu byinshi, usanga umwaka umwe umara igihe gito. Urugero n’uko hashize imyaka miliyoni 10, uruzi rwa Colorado rumize igice kimwe cy’ubutaka bw’ikibaya cya “Grand Canyon”, mu by’ukuri ugendeye kuri iyo myaka miliyoni 10 ishyize ikibaya cya Canyon gisadutsemo kabiri, ntago wavuga ko umwaka umwe ari muremure, ndetse bishobora no kugutera kutawubara nk’uwabayeho.
Abahanga mu bumenyi bw’Isi, bakoze ubushakashatsi ku bihe byaranze Isi n’imihindagurikire yayo, bavuga ko Isi imaze imyaka ibarirwa mu Mamiliyari, n’ubwo kuri ubu tuvuga ko turi mu mwaka wa 2020. Muri Siyansi ibintu byose byabaye, bigereranywa n’icyitwa “Geologic time” (igihe cyose cyashize kuva Isi yabaho). Muri siyansi babara ko, Isi imaze imyaka Miliyari 4.6, urumva ko ugereranyije n’imyaka ishize “Grand Canyon” isadutse, wavuga ko Canyon ari akana.
Hagendewe ku bitare, n’ibisigarizwa by’inyamaswa n’ibimera (Rocks and fossils), abasiyantifike basanze Isi yarabayeho mu bihe 4, kugeza uyu munsi turiho. Ibyo bihe nibyo byitwa “Era”, nabyo bikaba bigabanyijemo ibindi bihe bito byitwa “Period”, nazo zikaba zigabanyijemo ibihe bito cyane aribyo bise “Epoch” mu cyongereza cyangwa “Epoque” mu gifaransa.
Ibihe 4, Isi yabayemo harimo igihe cyitwa “Precambrian Era” akaba ari nacyo gihe kirekire kurusha ibindi byose, kuko cyihariye 85% bya Geologic time (igihe cyose cyabayeho). Igihe cya Precambrian Era cyatangiye kuva Isi yabaho kirangira mu myaka Miliyoni 570 ishyize. Icyo gihe ibinyabuzima byoroheje byatangiye kugaragara ku Isi nibura nko mu myaka Miliyari 3.5 ishyize, kandi nabwo ibinyabuzima byariho byari Algae, Fungi na Bacteria gusa.
Hakurikiyeho “Paleozoic Era”, iki gihe cyatangiye kuva mu myaka Miliyoni 570 ishyize, kigeza mu myaka Miliyoni 230 ishyize. Nicyo gihe mu nyanja hatangiye kubonekamo ibinyabuzima byinshi, ni nabwo ibimera n’inyamaswa byo ku butaka byatangiye kubaho. Muri Paleozoic Era, Isi yagiye igira impinduka nyinshi cyane, urugero n’uko imisozi ya “Appalachian” yo mu burasirazuba bwa Leta Zunze ubumwe za Amerika aribwo yabayeho.
Hakurikiyeho igihe cyitwa “Mesozoic Era”, cyatangiye mu myaka Miliyoni 230 ishyize kirangira mu myaka Miliyoni 65 ishyize. Icyo gihe ubuzima bwari buri kuboneka neza, kuko ibiti, inyamabere ntoya n’inyoni nibwo byagaragaye bwa mbere ku Isi. Gusa nanone “Mesozoic Era” bakunze kuyita “Age of Reptiles (igihe cy’ibikururanda: inyamaswa zikurura inda)”. Ibikururanda (Reptiles) byamenyekanye cyane ni “Dinosaurs”. Gusa iyo urebye mu buryo butandukanye usanga Dinosaurs zari nk’inyamaswa tubona uyu munsi. Kuko zimwe zaryaga inyama, izindi zirya ibimera, zimwe zari nini cyane kurusha inzovu, mu gihe izindi zari ntoya nk’inkoko, zimwe zagenderaga mu matsinda, mu gihe hari izagendaga zonyine, ndetse n’amabara yazo yari atandukanye. Igihe cya “Mesozoic Era” kirangwa cyane n’irangira rya Dinosaurs.
Igihe cya 4, ari nacyo turimo kugeza uyu munsi, ni igihe cyitwa “Cenozoic Era”. Cyatangiye mu myaka Miliyoni 65 ishyize n’ubu ntiturakivamo! Muri iki gihe za Alps n’imisozi ya Himalaya nibwo yatangiye kwihuza muri ako gace. Nyuma yaho muri iki gihe cya Cenozoic Era, nibwo igice kinini cy’ubutaka cyari gitwikiriwe n’urubura (ice), mu myaka Miliyoni 2 ishyize nibwo urwo rubura rwatangiye gukora ibi ibiyaga binini tubona uyu munsi.
Aya mateka dukesha igitabo “Earth Science P282-296” avuga ko igihe cya “Cenozoic Era” nanone kizwi ku izina rya “Age of Mammals (igihe cy’inyamabere)”, gusa Dinosaurs zimaze gucika ku Isi, nibwo inyamaswa z’inyamabere zabashije kubaho no kugwira. Inyamabere zirimo n’Abantu akaba aribwo bwoko bwiganje ku Isi. Uko igihe gikomeza, niko n’ubuzima buhinduka, ndetse hakaboneka n’ibindi binyabuzima bishya, cyangwa se indi miterere y’Isi mishya.
Muri make ugereranyije amateka y’Isi, n’umwaka umwe wo kuri Calendar (Kalindari), wavuga ko igihe cya Precambrian Era, ari amezi 10 ya mbere agize umwaka, noneho ibihe bya Paleozoic Era, Mesozoic Era na Cenozoic Era bikaba bingana n’amezi 2 ya nyuma y’umwaka. Bisobanura ngo ni nkaho “igihe cya Cenozoic Era” ari nacyo kuri ubu turimo kingana n’iminsi 5 n’amasaha 21 ugereranyije n’umwaka wo kuri kalindandiri.