yle ▁elabor ated ▁on ▁this ▁prem ise ▁by ▁arg uing ▁that ▁evol ved ▁stars ▁called ▁red ▁gi ants ▁created ▁many ▁elements ▁heav ier ▁than ▁hydro gen ▁and ▁hel ium ▁in ▁their ▁cores . ▁When ▁a ▁red ▁giant ▁finally ▁cast s ▁off ▁its ▁outer ▁layers , ▁these ▁elements ▁would ▁then ▁be ▁rec yc led ▁to ▁form ▁other ▁star ▁systems . ▁ ▁Form ation ▁ ▁Pres olar ▁ne b ula ▁The ▁ne b ular ▁hypothesis ▁says ▁that ▁the ▁Sol ar ▁System ▁formed ▁from ▁the ▁gravit ational ▁collapse ▁of ▁a ▁fragment ▁of ▁a ▁giant ▁mole cular ▁cloud . ▁The ▁cloud ▁was ▁about ▁ 2 0   par sec ▁( 6 5 ▁light ▁years ) ▁across , ▁while ▁the ▁fragments ▁were ▁roughly ▁ 1   par sec ▁( three ▁and ▁a ▁quarter ▁light - year s ) ▁across . ▁The ▁further ▁collapse ▁of ▁the ▁fragments ▁led ▁to ▁the ▁formation ▁of ▁dense ▁cores ▁ 0 . 0 1 – 0 . 1   par sec ▁( 2 , 0 0 0 – 2 0 , 0 0 0   AU ) ▁in ▁size . ▁One ▁of ▁these ▁col laps ing ▁fragments ▁( known ▁as ▁the ▁pres olar ▁ne b ula ) ▁formed ▁what ▁became ▁the ▁Sol ar ▁System . ▁The ▁composition ▁of ▁this ▁region ▁with ▁a ▁mass ▁just ▁over ▁that ▁of ▁the ▁Sun ▁() ▁was ▁about ▁the ▁same ▁as ▁that ▁of ▁the ▁Sun ▁today , ▁with ▁hydro gen , ▁along ▁with ▁hel ium ▁and ▁trace ▁amounts ▁of ▁l ith ium ▁produced ▁by ▁Big ▁Bang ▁nucle os yn thesis