. ▁ ▁The ▁common ▁parad ig m ▁is ▁that ▁the ▁event ▁was ▁caused ▁by ▁a ▁solar ▁particle ▁event ▁( S PE ), ▁or ▁a ▁consequence ▁of ▁events ▁as ▁often ▁happen , ▁from ▁a ▁very ▁strong ▁solar ▁f lare , ▁perhaps ▁the ▁strong est ▁ever ▁known ▁but ▁still ▁within ▁the ▁Sun ' s ▁ab ilities . ▁Another ▁discussed ▁scenario ▁of ▁the ▁event ▁origin , ▁involving ▁a ▁g amma - ray ▁burst , ▁appears ▁unlikely , ▁since ▁the ▁event ▁was ▁also ▁observed ▁in ▁is ot op es ▁ ▁and ▁. ▁ ▁Fre quency ▁of ▁similar ▁events ▁ ▁The ▁event ▁of ▁ 7 7 4 ▁is ▁the ▁strong est ▁sp ike ▁over ▁the ▁last ▁ 1 1 , 0 0 0 ▁years ▁in ▁the ▁record ▁of ▁cosm ogen ic ▁is ot op es , ▁but ▁it ▁is ▁not ▁unique . ▁A ▁similar ▁event ▁occurred ▁in ▁ 9 9 3 ▁or ▁ 9 9 4 , ▁but ▁it ▁was ▁only ▁ 0 . 6 ▁times ▁as ▁strong ▁as ▁well ▁as ▁another ▁event ▁of ▁c . ▁ 6 6 0 ▁B CE . ▁Several ▁other ▁events ▁of ▁the ▁same ▁kind ▁are ▁also ▁sus pected ▁to ▁have ▁occurred ▁during ▁the ▁Hol oc ene ▁epo ch . ▁ ▁From ▁these ▁statistics , ▁one ▁may ▁expect ▁that ▁such ▁strong ▁events ▁occur ▁once ▁per ▁tens ▁of ▁mill enn ia , ▁while ▁we aker ▁events ▁may ▁occur ▁once ▁per ▁mill en ni um ▁or ▁even ▁century . ▁The ▁event ▁of ▁ 7 7 4 ▁did ▁not ▁cause ▁cat ast roph ic ▁consequences ▁for