Final answer:
A biomarker is a measurable indicator of a biological state or condition, often used to diagnose health conditions or to detect the presence of contaminants or life. Medical examples include proteins that denote certain diseases, while in astrobiology, they might refer to atmospheric signs of life.
Step-by-step explanation:
A biomarker is c) a measurable indicator of a biological state or condition. Essentially, it is a molecule, often a protein, that can be associated with a specific biological process, disease state, or environmental exposure. Biomarkers can be used in a clinical setting to diagnose health conditions or in environmental sciences to indicate the presence of life or contaminants.
Biomarkers are critical for early detection of diseases. For example, in medical research, proteins expressed by cells may serve as biomarkers for cancer or other diseases. The identification and study of biomarkers involves various technological methods, such as mass spectrometry to assess the 'fingerprints' of these markers in biological samples.
In the search for life beyond Earth, scientists may look for biomarkers that indicate the presence of life on other planets, which could include certain atmospheric compositions or organic molecules.