পারমিয়ান গন বিলুপ্তির কারণ কি ঘটেছিল ২৫ কোটি বছর আগে?
Cause of Permian extinctions; In 252 Million years ago what happened?
Already Earth has past its 4.5 Billion Years. And through this interval of time earth has experienced 5 mage mass extinction. One of them is the Permian Triassic mass extinction. The main reason for this great dying event is still a great concern among the geologist, paleontologist. The main reason for extinction is mainly two
1. External cause; The meteorite impact from the outer space
2. Internal cause; Siberian flood basalt volcanism, sea-level change, the ocean anoxic events (detoxification), global warming due to the huge release of the under ocean methane clathrates, The water collum stratification, Ocean acidification, etc.
Recent Findings with the Biomarker Study:
One of the recent findings is the input of terrestrial organic matter which caused the excess primary production in the ocean and finally, the ocean became anoxic (no oxygen in the ocean water). The biomarker study can play a role to investigate that finding. The biomarker is the geochemical stable compounds that are formed after the diagenetic and cytogenetic effects of the buried organic matter. Like, Pristane and Phytane.
The biomarker can tell us the past depositional environments and the clue of the past event. Hopanoid is a larger group of compounds formed from the lipids. Then after diagenesis and catagenesis it stops and remains in the sediments as a Hopane, Moretane, etc. Hopane and Moretane are the same hopanoid group of geochemical fossils preserved in the sedimentary source rocks. C30 ab hopane is more stable than Montane. Usually, in the petroleum source rocks preservation of hopane and Moretane ration are 20:1. The amount of hopane than Moretane in the source rocks depends on the maturation of the rocks. The more mature or the abundance of hopane than moretane. During the categenesis the mostly we found hopane than moretane. In the GC MSMS we can measure the hopane and moretane by the Multiple Reaction monitoring methods (MRM) from the aliphatic compound samples (F1a). The Mass fragments (m/z) for identification of hopane and moretane are the same as (M/z; MRM 412.5- 191.3) but the main trick to identify hopene and moretane separately is the Kovats index value. The value of Kovats indices of C30 αβ Hopan (MRM 412.5- 191.3) and Moretane (MRM 412.5- 191.3) is 3068 and 3106 respectively. In the GC MSMS chromatogram, the C30 αβ Hopan (MRM 412.5- 191.3) appears first then the peak of moretane will appear and the M/Z is same as the C30 αβ Hopan (MRM 412.5- 191.3) because moretane is the diagenetic product of hopane group but less stable hence less abundance than ab hopane. Moretane will appear just 0.5 min later than C30 αβ Hopan (MRM 412.5- 191.3).
In sedimentary rocks hopanes are the most abundant geochemical marker usually hopane is produced by bacterial synthesis. The hopane has 5 stereoisomers like aa C30 Hopan, ab C30 Hopan bb C30 Hopane and ba C30 Hopane. Among them, ab hopane is more stable after the sedimentary diagenesis and categenesis. The ba c30 hopane is also called the Moretane. The ratio of ab C30 Hopan/Moretane is the marker for the identification of the maturity in the Petroleum industry even in the geological study. The Moretane is usually more in the immature rocks and in the peat, coal enriches sediments.
For the identification of the Permian Mass extinction this hopane and moretan ratio paly a major role. Scientists discovered the Permian marine extinction (252 million years ago) one of the causes is the excess input of the terrestrial organic matter. They found the increased value of the hopane/moretane ratio from the Meishan Section (The Global stratotype and section point) in South China. This discovery indicates the excess input of terrestrial organic matter in marine sediments.
Terrestrial input to the marine environments is due to the collapse of the tree and land plants during the Permian age which ultimately one of the causes of the great dying, especially for the marine environments. Still, Scientist needs to identify the effect of the extinction which had affected in the land plants. So, we need to identify the same hopane/ moretane anomaly for the terrestrial sample.