▁there ▁can ▁be ▁R ifts , ▁areas ▁where ▁the ▁land ▁is ▁beginning ▁to ▁spread ▁apart . ▁ ▁Ocean ography ▁ ▁Adv ances ▁in ▁physical ▁ocean ography ▁occurred ▁in ▁the ▁ 2 0 th ▁century . ▁Sea ▁depth ▁by ▁ac oust ic ▁measurements ▁was ▁first ▁made ▁in ▁ 1 9 1 4 . ▁The ▁German ▁" M eteor " ▁expedition ▁gathered ▁ 7 0 , 0 0 0 ▁ocean ▁depth ▁measurements ▁using ▁an ▁echo ▁sound er , ▁surve ying ▁the ▁Mid - At l antic ▁R idge ▁between ▁ 1 9 2 5 ▁and ▁ 1 9 2 7 . ▁The ▁Great ▁Global ▁R ift ▁was ▁discovered ▁by ▁Maurice ▁E wing ▁and ▁Bruce ▁He e zen ▁in ▁ 1 9 5 3 , ▁and ▁the ▁mountain ▁range ▁under ▁the ▁Ar ctic ▁was ▁found ▁in ▁ 1 9 5 4 ▁by ▁the ▁Ar ctic ▁Institute ▁of ▁the ▁USS R . ▁The ▁theory ▁of ▁se af loor ▁spread ing ▁was ▁developed ▁in ▁ 1 9 6 0 ▁by ▁Harry ▁Hamm ond ▁H ess . ▁The ▁Ocean ▁Dr illing ▁Program ▁started ▁in ▁ 1 9 6 6 . ▁There ▁has ▁been ▁much ▁emphas is ▁on ▁the ▁application ▁of ▁large ▁scale ▁computers ▁to ▁ocean ography ▁to ▁allow ▁numerical ▁predictions ▁of ▁ocean ▁conditions ▁and ▁as ▁a ▁part ▁of ▁overall ▁environmental ▁change ▁prediction . ▁ ▁Ge om agnet ism ▁▁ ▁The ▁motion ▁of ▁the ▁conduct ive ▁mol ten ▁metal ▁beneath ▁the ▁Earth ' s ▁cr ust , ▁or ▁the ▁Earth ' s ▁dynam o , ▁is ▁responsible ▁for ▁the ▁existence