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What is a biomarker?
in general...
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.
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stromatolites, believed to be one of the earliest forms of life on earth. remnants of them can be found in the very old geologic record, and we know what they are because they still exist today, like the ones you see here. photo courtesy of R.V. Burne
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reconstructing early life from organic matter
Molecular fossils that are stable under geological conditions mostly originate from biological lipids. 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. Therefore, biomarkers offer a powerful means to study geobiology, life and its interaction with the environment as recorded in rocks of Precambrian (543 million years old) age and older. Structural and isotopic information allow them to be distinguished from abiogenic organic compounds that exist throughout the cosmos. Thus, biomarkers are an important tool in searching for extraterrestrial life.
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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, which shows you what we have learned about the evolution of life through studying biomarkers.
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age distribution of sediments from well-preserved organic matter.
adapted from Treatise on Geochemistry review, Vol. 8, Chapter 3; Brocks and Summons |
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