@article{small,
  title={The structure and distribution of carbon in 3.5 Ga Apex chert:Implications for the biogenicity of Earth‘s oldest putative microfossils},
  author={Gregorio, Bradley T. De and Sharp, Thomas G.},
  journal={American Mineralogist},
  volume={91},
  pages={784–789},
  year={2006},
  doi={10.2138/am.2006.2149}
}