ABSTRACT
The term biomarker is a contraction of the expression ‘biological marker compound’ and is used in a variety of scientific disciplines. In palaeoclimate studies it is used to refer to organic molecules, i.e. carbon-based, of relatively low molecular weight (usually less than 1000 mass units), which are found in sediments (see examples in Fig. 24.1). These compounds were initially produced by a variety of organisms either on land or in the aquatic environment. The key factor that determines the value of these molecules (natural products) in palaeoclimate studies is that after their biosynthesis, and the death of the source organisms, they survived deposition to sediments in a recognisable form in terms of their original structure and sterical configuration (i.e. spatial distribution of the atoms). They can thus be considered chemical fossils (Eglinton and Calvin, 1967). The success of these organic components as palaeoproxies largely depends on their resilience to early degradation processes during sedimentation and after incorporation into the sediment.
