L1 - Organic geochemistry introduction Flashcards
what is organic chemistry?
The study of the transformation undergone by organic matter (both biological and manmade) in Earth’s systems, particularly focusing on the transition from biosphere to geosphere.
What is a biomarker?
An organic compound in natural waters, sediments, soils, fossils, crude oils, or coals that can be unambiguously linked to specific precursor molecules made by living organisms.
Why is DNA considered the ultimate biomarker?
DNA contains the highest source of specific information, though it doesn’t preserve well over time.
What are the three major domains that contain terrestrial and marine biomarkers?
Bacteria, Eucarya, and Archaea.
What makes green sulfur bacteria significant in biomarker studies?
They contain specific compounds not found anywhere else, indicating a photic zone environment when present.
What is the progression sequence of organic matter maturation?
Extant biomass → diagenesis → kerogen and bitumen → catagenesis → oil, coal, and gas.
What’s the difference between immature and mature organic matter?
Immature organic matter is fresh, while mature organic matter has been transformed into petroleum.
Is maturity equivalent to time in organic matter?
No, maturity is not equivalent to time - old sediments can still be fresh.
What is the Carbon Preference Index (CPI), and what does it indicate?
CPI measures the ratio of odd to even carbon numbers. Fresh organic matter has odd>even (>4), while mature organic matter has odd=even (≈1).
What is the reaction sequence for high molecular weight n-alkanes?
Acytyl coenzyme A (2 carbon atoms added) → N-alkanoic acids (even) → N-alkanes (odd and CO2 loss).
What is a proxy in organic geochemistry?
A parameter that uses empirically determined variables to estimate some other variable that cannot be measured directly.
What are the three main categories of proxies in organic geochemistry?
Water column proxies, sediment proxies, and thermal maturity proxies.
Name three water column proxies.
CO2[aq], nutrient richness, and productivity (among others like temperature, CH4 cycling, hypersalinity, stratification).
What is a lipid?
A chemical compound that is insoluble in water but soluble in organic solvents.
Why are phospholipids (PLFAs) useful as biomarkers?
They can be used as markers of ‘living biomass’ because they fall apart relatively fast after death.
What are the main products of isoprenoid biosynthesis?
- Tetracyclic Triterpenoids (steroids)
- Pentacyclic triterpenoids (oleanoids, ursanoids, lupanoids, hopanoids)
- Tetraterpenoids (GDGTs, carotenoids)
- Tetrapyrrole pigments
How can carbon isotope analysis be used to study environmental conditions?
Through compound-specific 13C and 14C analysis, it can determine relative C3-C4 plant composition, indicating wet or arid climate conditions.
What does PAH analysis of air samples from Sweden reveal?
It shows that polyaromatic hydrocarbons come equally from biomass burning (50%) and fossil fuels (50%), unlike Greece and Croatia which are mostly fossil fuel-derived
