What is a biomarker?
This question might be asked by a medical student medical professional geological student or professional. Searching on the internet and writing “What is a Biomarker” will find many results but one is for the medical student and the other is for geological students namely all are the same because the biomarker is the end product from source organic matter.
The biomarker is the proxy for the paleoenvironment interpretation. The biomarker is named a biomarker that is related to the geological study. When an organic matter is discomposed, by some diagenetic processes, then some more stable organic matter is produced and they are called the biomarker or the geo-biomarker, the molecular fossils or geochemical fossils.
What is a biomarker and its application:
Biomarkers are generally derived from the lipids of organic matter. Suppose, Pristane, is a molecular fossil that indicates the redox environments and is widely recognized as a redox proxy.
How Biomarkers/molecular fossils are formed?
We can give an example of the production of Pristane in the sediments (Tetramethylepenta decane). Pristane is the branched acyclic isoprenoid containing 19 carbon atoms. A prominent peak of the Pristane elutes just after the C17 n-alkane peak in the Gas chromatography-mass spectrometry (GCMS) measurements.
The original source for the Pristane (Pr) is the phytol. Phytol is derived from Phytyle, a major chain off of the chlorophyll-a molecule from the tree leaf. If phytol undergoes diagenesis and categenesis then pristane and phytane (another related biomarker) are produced.
Pristane produces with the oxidation and by the decarboxylation of the phytol. The phytane has the carbon 20 atom, and is produced by the dehydration of the phytol and remain in the sediments as they are most stable. Some important biomarkers in the paleoenvironments study and petroleum industry.
Moretane and hopane are the most important biomarkers in geochemistry for identifying the maturity of rocks and paleoenvironments of the past.
What is a biomarker and what is the list of important biomarkers:
Pristane (Pr), Phytane (Ph), Phenanthrene (Phe), Dibenzothiophene (DBF), Cadalane, Retane, DBF/Phe, Cadalane/Phe, Bonzo(e)pyrene, n-alkane, C33ACH (C33 n-alkane cyclohexane), Metane, Hopane, Sterane, Simonelite, coronene, Isorenairatane, 2-Methyl hopane, etc.
How do we know the soil erosion event occurred in the past?
The high value of the Pr/Ph ratio indicates the oxic condition in the soil or marine depositional environments. Hence, the d13 Corg positive shift indicates the relation between the soil erosion event and deposited sediments in the ocean bottom as the high value of the Pr/Ph in the ocean sediments indicates the oxic environments as for the incorporation of more soil from the land. On the other hand, DBF/Phe high value also indicates the soil erosion event. So it must be seen the high value if there is a soil erosion event. The value of the Cadalane is also very important to make a correlation among them.
Because Cadalane is usually derived from the higher plants of terrestrial environments. Cadalane, retane, and Simonelite are all derived from higher plants, so, in the soil erosion events, the high value of Cadalane, retane, and Simonelite will be prominent in the rock samples. Another, evidence of the soil erosion event is the dominance of the higher n-alkane like, C25 n-alkane to C35 n-alkane.
Because these higher chain n-alkanes are usually derived from the higher plants or trees that contain higher cellulose. Hence, higher n-alkane is another proxy for the identification of soil erosion events. The total organic carbon from that sample will be high due to the incorporation of high organic matter during the soil erosion events.
Soil carries lots of organic matter along with the soil grain and is deposited in the ocean bottom. Hence, the TOC value will be higher in the rock samples. Soil erosion events may occur in many ways, like, huge volcanic eruptions, forest fires, meteorite impacts, etc, The main cause of the soil erosion event can be identified based on some important biomarker proxy, and among them, the Coronene index is one of them.
What is a Biomarker as a Coronene index can differentiate the forest fire and meteorite impact event
Coronene index indicates the event whether it was a forest fire, volcanic eruption, or massive meteorite impact based on the value of the Coronene index.
The coronene index=coronene/coronene+benzo (a) pyrene + benzo (g,h, i) pyrelene. This coronene index value increases if any extraterrestrial body hits the planet Earth where a higher amount of organic-rich sediment exists.
The combustion of coal or petroleum beneath the ground will produce a higher amount of coronene. A value of the coronene index higher than 0.8 indicates the meteorite impacts, less than 0.8-0.5 is for volcanic eruption and below 0.5 is for a forest fire event.
So, based on the observation of the coronene index value geologists can interpret paleo events like soil erosion events due to a forest fire volcanic eruption or meteorite impacts.
The evidence is the real fact because the coronene production in the rock sample depends on the heat used during the soil burning. If more than 4000 degrees Celcius is applied, a relatively higher amount of coronene will be produced, and if less heat is applied then less amount.
So, the coronene production in a rock sample is directly proportional to the heat applied. As the meteorite impact imposes huge heat in the soil hence high amount of coronene will be produced.
