Siza unikeze uhlu olulula lwezizathu zokuthi kungenzeka yini ukuthi ubuhlakani bangaphandle komhlaba abukho noma buyivelakancane kakhulu
Context:Labo abacabanga ukuthi ukuphila okuhlakaniphile ngaphandle komhlaba (cishe) akunakwenzeka baphikisa ngokuthi izimo ezidingekayo ekuziphendukeleni kwemvelo kokuphila - noma okungenani ukuziphendukela kwemvelo okuyinkimbinkimbi - azivamile noma ziyingqayizivele eMhlabeni. Ngaphansi kwalokhu kucabanga, okubizwa ngokuthi i-Rare Earth hypothesis, okuwukwenqaba isimiso sokulinganisela, ukuphila okuyinkimbinkimbi kwamangqamuzana amaningi kubhekwa njengokungavamile kakhulu.  Umbono we-Rare Earth uthi ukuvela kokuyinkimbinkimbi kwezinto eziphilayo kudinga izimo eziningi ezingahleliwe, njenge-galactic habitable zone, inkanyezi neplanethi (s) enezimo ezidingekayo, njengokwanele kwendawo yokuhlala eqhubekayo, inzuzo yomgcini omkhulu onjengoJupiter nenyanga enkulu, izimo ezidingekayo ukuqinisekisa ukuthi iplanethi ine-magnetosphere ne-plate tectonics, i-chemistry ye-lithosphere, umkhathi, nolwandle, indima "yamaphampu wokuziphendukela kwemvelo" njenge-glaciation enkulu nokuhlaselwa okungavamile kwe-bolide. Futhi mhlawumbe okubaluleke kakhulu, ukuphila okuthuthukile kudinga noma yini eyaholela ekuguqulweni kwamangqamuzana e-prokaryotic (amanye) abe amangqamuzana e-eukaryotic, ukukhiqiza kabusha ngokocansi nokuqhuma kweCambrian.  Encwadini yakhe ethi Wonderful Life (1989), uStephen Jay Gould wasikisela ukuthi uma "itape lokuphila" lalingase ligoqelwe emuva esikhathini sokuqhuma kweCambrian, futhi kwenziwe ukulungisa okukodwa noma okubili, cishe abantu babengasoze bavela. Abanye abacabangi abanjengoFontana, uBuss, noKauffman baye babhala ngezimfanelo zokuphila ezizihlelayo.
Izimo ezabangela ukuba ukuphila okuhlakaniphile kuvele emhlabeni kungenzeka zingavamile kakhulu endaweni yonke. Kucatshangwa ukuthi lezi zizathu yilezi: 1. Izinkomo Isimiso sonozungezilanga sisendaweni ephephile ngaphakathi komthala waso. 2. Izingelosi Indawo umhlaba okuyo uma uqhathaniswa nelanga namanye amaplanethi asesimisweni sonozungezilanga iwuvikela ezimweni zemvelo ezimbi kakhulu ezingavimbela ukuphila. 3. Izindaba Ezinhle Izinyathelo ezaholela ekuthuthukeni kwezinhlobo zokuphila (ukusuka kumangqamuzana e-prokaryotic kuya kumangqamuzana e-eukaryotic, ukuzala ngokocansi nokuqhuma kwe-Cambrian) kungenzeka zingenzeki.