After a volcanic eruption, airborne lichen spores settle on the bare, cooled rock. A scientist studies the lichens and changes to the biotic and abiotic factors of the area. She monitors the acid released by the lichens and tracks the rate at which the rock breaks down into soil. She also collects data on the level of nutrients in the soil and tracks the decay of dead lichen. As she monitors the formation of soil she concludes that lichens release acid that helps break down the rock and create soil, and that the lichens add nutrients to the soil as they die and decay. Based on the data she collected, which question was the scientist most likely trying to answer?

a
How deep does soil need to be to support the growth of grasses, flowers, and trees?
b
How long after a volcanic eruption do mosses and ferns begin to grow?
c
How do lichens contribute to primary succession?
d
How long after a volcanic eruption can newly formed soil hold water?