Most BIF occurs in rocks older than 1850 million years and is believed to have formed at a time when the atmosphere had little free oxygen, and seawater in the deep ocean contained abundant iron.
(BIF; is believed; ) (the atmosphere; had; little free oxygen; T:a time) (seawater in the deep ocean; contained; abundant iron)
BIF the atmosphere seawater in the deep ocean
is believed had contained
little free oxygen T:a time
abundant iron