The rock record of early Earth contains numerous examples of microscopic organic filaments and spheres, commonly interpreted as fossil microorganisms. Microfossils are among the oldest traces of life on our planet, making their correct identification crucial to our understanding of early biological evolution. They are furthermore potential targets for astrobiological investigations on rocky planets. Yet, spherical and filamentous microscopic objects composed of organic carbon and sulfur can form in the abiogenic reaction of sulfide with soluble organic compounds. These objects, called organic biomorphs, spontaneously form by self-assembly in aqueous solutions containing sulfide. These biomorphs adopt a diversity of morphologies that closely mimic a number of microfossils from the ancient rock record. Here, I will present results on the formation of the C-S biomorphs under geochemical conditions relevant to Hadean and Archean environments, and discuss possible implications for prebiological compartmentalization on early Earth.