Question

which of these occurs at the start of primary succession?
wildfires appear causing groups of animals to flee
lichens and mosses begin breaking down rock into soil
biotic life begins to grow, restarting the ecosystem

Explanation:

Primary succession occurs in an area with no pre - existing soil. Lichens and mosses (pioneer species) break down rock (through chemical and physical means) to form soil. Wildfires are more related to secondary succession (as there is already soil and some remnants of the previous ecosystem). The statement about biotic life restarting the ecosystem is too vague compared to the specific role of lichens and mosses in primary succession.

Answer:

lichens and mosses begin breaking down rock into soil