Select the correct answer from each drop-down menu : Compared to modern Earth, Precambrian Earth's atmosphere and oceans were much richer in
because it was so prevalent in
.

A. carbon dioxide, oxygen, salt

B. volcanic gas, single-called organisms, crustal rock

a

Explanation:

you got to think single cell organisms were not abundant however the Co2  and salt compounds were as well as the oxygen needed to help evolve them which led the moncellular creatures to evolve into algae and fungi and then those 2 formed a symbiotic relationship to form lichen

Breeding ground

Explanation:

high levels of oxygen provide necessary material and aquatic insects provide a food source for the new hatchlings.