Composition and higher-order structure in nucleic acids sequenced from a chondrite

Abstract The known tree of life occupies an infinitesimal region of the space of all mathematically possible evolutionary histories, yet our sequence analysis frameworks are implicitly calibrated to it and to its associated compositional and grammatical regularities. Here we analyze nucleic acid molecules sequenced from the Zag meteorite as part of a broader effort to understand how nucleic acid sequence composition and higher-order structure are shaped under chemically divergent environments. We characterize these sequences across multiple analytical layers, and show that they lack signatures of protein-coding organization, translational periodicity, or known biological grammar. At the same time, they deviate significantly from random or composition-only null models, displaying constrained complexity and low-dimensional structure in k -mer frequency space. Multiple tests place amplification and sequencing-driven artifacts and metagenomic contaminants at a low likelihood. Taken together, these findings indicate that the Zag sequences occupy an unusual region of sequence space that is not readily accounted for by known biological or technical models, thereby narrowing, but not resolving, the range of plausible explanations and motivating independent replication and further investigation.