As oxygen appeared in the atmosphere, ________ also accumulated, which formed a protective barrier that protects the Earth from ________.
A. ozone / UV radiation
B. elemental sulfur / volcanism
C. ferrous iron / hydroxylating radicals
D. sulfate / hydrogen sulfide
Answer:A
As oxygen appeared in the atmosphere, ________ also accumulated, which formed a protective barrier that protects the Earth from ________.
A. ozone / UV radiation B. elemental sulfur / volcanism C. ferrous iron / hydroxylating radicals D. sulfate / hydrogen sulfide