Final answer:
Lichens would be found first on newly formed rock, serving as pioneer species that begin the soil formation process essential for succeeding plant growth.
Step-by-step explanation:
The organism that would be found first on newly formed rock is lichens. Lichens act as pioneer species in primary succession, beginning the process of soil formation on barren landscapes such as new land formed from volcanic activity.
Lichens are symbiotic organisms comprised of a fungus and an alga or cyanobacteria. They have the unique capability to colonize harsh environments like bare rock because they can photosynthesize and do not rely on soil, with the fungus absorbing minerals and nutrients from the rock, while the alga or cyanobacteria provides sugary food through photosynthesis. Their growth results in the breakdown of rock, which is crucial for soil development that enables subsequent colonization by other organisms like mosses, ferns, and ultimately grass.