Biomolecules refer to high-molecular-weight organic molecules found in living organisms, such as proteins, nucleic acids, lipids, and sugars. Biomolecules are the fundamental building blocks of life and play important biological roles in organisms. Among them, nucleic acids serve as the core carriers for storing and transmitting genetic information; proteins have diverse functions, including catalytic roles in cell construction and regulation of metabolism; sugars serve as energy storage substances and structural components of cells; and lipids are the basic units of cell membranes. These biomolecules are composed of carbon, hydrogen, oxygen, and nitrogen, which are bonded together by various chemical bonds.
Over long periods of time, biomolecular fossils that have been preserved under geological conditions are typically composed of the hydrocarbon skeletons of lipid compounds. These derivatives are often referred to as biomarker compounds or molecular fossils. Currently, research on biomarker compounds has covered four main biochemical components—proteins (including nucleic acids), sugars (including chitin), lipids, and lignin, with lipids and proteins being the most extensively studied. Biomarker compounds help scientists supplement or refine fossil records, and their carbon and hydrogen isotopes also record the position and role of their parent organisms in ancient ecosystems, the elemental chemical background of the surrounding environment, and the evolutionary history of ancient temperatures. Today, biomarker compounds play a crucial role in exploring the origin of early life on Earth, major geological events, and reconstructing gaps in traditional fossil records.
Petroleum formed by organisms contains some biomolecular fossils. Some biomarker compounds are closely related to modern special organisms. Through comparative studies, people have gained a deeper understanding of the evolutionary history of these organisms. For example, dinoflagellates and diatoms are important oxygen producers on Earth, with their earliest fossil records dating back to the Middle Triassic and Jurassic periods, respectively. However, molecular fossils derived from these algae, such as dinoflagellate sterols and 24-hydroxysterols, have shown high concentrations in strata since the Middle Triassic and Jurassic periods. Based on the distribution of triaromatic dinoflagellate sterols, researchers proposed that the ancestors of dinoflagellates may have first appeared in the Devonian or Precambrian periods. In the late Middle Ordovician strata of Yongji, Shanxi Province, organic structures (organic walls) similar in morphology and ultrastructure to dinoflagellates were found, along with the detection of dinoflagellate biomarker compounds—dinoflagellate sterols. This result has advanced the record of dinoflagellate molecular fossils by 100 million to 400 million years and the possible record of solid fossils by 700 million to 900 million years.