Organic Geochemistry Laboratory - What are biomarkers?
Lipid biomarkers (molecular fossils) are organic compounds originating from living organisms and can be used in environmental and climatic reconstructions and petroleum research.
Biomarkers are also called chemical fossils, because similar to bones, these compounds can provide information on the producing organism, often even after chemical alteration of the original compound. This example shows cholesterol (chemical structure on left), a sterol that is typical for all eukaryotes (including animals and humans), degraded to its sterane derivative (chemical structure on right).
These compounds are tracers for environmental, depositional and climatic processes in soil, sediment, sedimentary rock and crude oil samples, allowing scientists to reconstruct past environmental conditions, understand human impacts on the environment, and trace sources of crude oil within sedimentary basins.
Examples of biomarkers (lipids) found in environmental samples. Chlorophyll a is the main pigment in plants, archaeol is a common compound in archaea, ladderanes are diagnostic for anaerobic ammonium oxidizing (anammox) bacteria, and cholesterol a widespread indicator of eukaryotes, which include humans.
Applications
- Environmental and climate research
We can use the concentration and compound-specific isotopic composition of biomarkers to reconstruct water column and air temperatures, pH values, salinity, stratification or redox conditions, pollution levels, and vegetation changes, giving us insight into human impacts, environmental and climate change. We can further learn about the evolution of life, distinguish between the sources of organic matter, study preservation and degradation of organic material and determine its age.
The compound-specific isotopic composition of biomarkers can also provide insight into the biogeochemical cycling of carbon (e.g., to learn about feedback on climate change, methane cycling), nitrogen (e.g., nutrient dynamics), hydrogen (e.g., precipitation), oxygen (e.g., paleotemperature reconstruction) and sulfur (e.g., preservation of organic matter).
- Petroleum research
We can use biomarkers to link crude oils back to their source rocks and to distinguish genetically related oil families. Biomarkers indicate the degree of thermal maturity and biodegradation of oils and enable interpretation of the age and depositional conditions of source rocks. This information helps scientists and oil exploration companies to understand where and when discovered oils were formed, and hence where to look for new oil fields.