The phosphate(主语)// was deposited(谓语动词)// by the decay of marine microorganisms(状语) (被动语态)

海洋微生物腐烂后沉积形成磷酸盐。

The decay of marine microorganisms(主语)// deposited(谓语动词)// the phosphate(宾语).(主动语态)

(1) phosphate  n.磷酸盐 

(2)deposit   vt.使沉积；使沉淀；使淤积

(3)decay  n.腐烂；腐朽

(4)marine microorganisms   海洋微生物