Molecular fossils are the unique molecular structure formed after the break down of the complex organic compounds by the decomposition of organic matter in the sedimentary rocks. Example are Pristine, Phytane, etc. These molecular fossils also called the “Biomarker”. The biomarker is the proxy for identifying any past depositional environments or past events. Like, Mass extinction events of the Paleo-earth history. From the sedimentary rock, the biomarker can be identified by the Gas Chromatogram Mass Spectrometry-Mass Spectrometry (GCMSMS) measurements. This is the most powerful tools in the oil and gas exploration field also.