The search for evidence of Earth's earliest life activities is a daunting challenge. Sedimentary rocks older than 3.6 Ga have undergone medium- to high-grade metamorphism, making it difficult to preserve fossil entities. The most plausible carriers of preserved biosignatures are graphitic carbon formed through biomass degradation and metamorphism. However, since abiotic processes can also generate graphite, previously reported biosignatures in rocks >3.6 Ga have been widely questioned. We summarizes current advances and ongoing controversies in the study of early life records. We further presents some recent progress in discriminating biosignatures within ancient metamorphosed sedimentary rocks through integrated micro-area analytical techniques. These findings aim to provide guidance for research on the origin of terrestrial life and the detection of life on Earth-like planets.

biosignatures,apatite,graphitic carbon,metasedimentary rocks