Name an abiotic factor that was once biotic.
Biotic features within an environment are living (bio means "life") substances within that environment. Examples could be plants, animals, fungi, decomposers, algae, etc.
Abiotic features of an environment are nonliving characteristics or features of that environment that have an impact on that environment. Examples of abiotic features include water, light, soil, temperature, rainfall, gases, pH, etc. These factors affect the survival and reproduction of biotic organisms within the environment.
An example of an abiotic feature of an environment that was once a biotic feature could be an empty seashell of a mollusk that is found along the shore of an ocean or a lake. The shell once served as the exoskeleton of a mollusk (clam, oyster, scallop, etc). However, once the mollusk passes, the shell is left behind. Eventually, the shell will be weathered by the tumbling of the ocean waves and currents. This process will cause the shell to break down into smaller pieces and become part of the beach's sand. The sand, in turn, is the habitat for other creatures such as crabs. Thus, the shell has become an abiotic substance that directly affects the survival of another organism in that environment.