Final answer:
Sodium ions have not been used as biomarkers since they are inorganic and do not contain carbon, which is essential for organic chemical signatures of life.
Step-by-step explanation:
Among the options provided in the question, sodium ions (3) sodium ions) have not been conventionally used as biomarkers or organic chemical signatures of once living organisms. Biomarkers are typically organic molecules that contain carbon and other elements such as hydrogen, nitrogen, oxygen, phosphorus, and sulfur – collectively known as the biogenic elements, or CHNOPS. Examples of organic biomarkers include cellular pigments and complex molecules that may contain carbon isotopes.
Carbon isotopes (like carbon-14) are used in radiocarbon dating to determine the age of organic artifacts. Oxygen isotopes can provide information about ancient climates and environments. Cellular pigments, found in living organisms, can indicate the presence of specific types of cells or organisms in ancient samples. Sodium ions, although essential for life, are inorganic and do not contain carbon; hence, they do not typically serve as organic chemical signatures of life.