Molecular biological markers, or biomarkers, are natural products that can be traced to a particular biological origin. They are powerful tools that can be used to trace diseases, drugs and environmental contaminants in modern systems. In our group, however, we use them to study ancient environments and the evolution of life on earth. The most effective biomarkers are organic compounds with specific biological sources, whose structures can be preserved through geologic time.
A few examples of lipids (Wikipedia commons)
Reconstructing early life from organic matter
Molecular fossils that are stable under geological conditions mostly originate from biological lipids. Lipids are a group of molecules that include fats and waxes, and they generally preserve better in sediments over long periods of time than molecules like DNA and proteins. These biomarkers encode information about ancient biodiversity, food chain associations and environmental conditions. They are recorders of element cycling, sediment and water chemistry, oxidation-reduction conditions and temperature histories. Most importantly, however, hydrocarbon biomarkers are stable for billions of years if they are enclosed in intact sedimentary rocks that have only suffered a mild thermal history (i.e. haven’t been heated up very much). Therefore, biomarkers offer a powerful means of studying geobiology—life and its interaction with the environment. Structural and isotopic information allow them to be distinguished from abiogenic (non-living) organic compounds that exist throughout the cosmos. Thus, biomarkers are also an important tool in searching for extraterrestrial life elsewhere in the universe.
How biomarkers are created and preserved in the geologic record
With that introduction, we can begin to get to the biological and geological processes that create and preserve biomarkers. Below is a geologic timescale from the beginning of the formation of the earth to the present day, which shows you what we have learned about the evolution of life through studying biomarkers.