Gloeocapsomorpha prisca (Fig. 1) is a microfossil (∼10µm) with an organic wall of uncertain biological affinity, probably a cyanobacterium1,2,4,6. This fossil microorganism constitutes the vast majority of the organic matter in “kukersite” rocks. G. prisca has been thoroughly studied by gas chromatography-mass spectrometry (GC-MS), using extractive techniques, chemolysis and pyrolysis1,2,3. Here we perform a pilot study in order to investigate the potential of laser-assisted mass spectrometry to analyze the molecular fingerprint of single microfossils. Bitumen and kerogen of a kukersite sample from a 460-million-year-old deposit of northwestern Russia5, were analyzed after organic solvent extractions and demineralization. We measure bulk thermo-desorption and pyrolysis parameters with Rock-Eval 7S. We use molecular characterization methods that allow analyses down to the scale of a single microfossil. We analyze kerogen by secondary ion time-of-flight mass spectrometry (ToF-SIMS), which combines extreme surface sensitivity with a spatial resolution of ∼1 µm. The kerogen is then analyzed with high resolution (HR-µL2-MS) two-step laser desorption-ionization mass spectrometry with a spatial resolution of 140 µm. We used very-high mass resolution Fourier transform ion cyclotron resonance mass spectrometry by laser desorption/ionization (LDI-FT-ICR-MS) on G. prisca aggregates (e.g., Fig. 1) with laser beams down to less than 20 µm.