Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.
The abiogenic petroleum origin is a fringe science which proposes that most of earth's petroleum and natural gas deposits were formed inorganically. Mainstream theories about the formation of hydrocarbons on earth point to an origin from the decomposition of long-dead organisms, though the existence of hydrocarbons on extraterrestrial bodies like Saturn's moon Titan indicates that hydrocarbons are sometimes naturally produced by inorganic means. Theories explaining the origin of petroleum as abiotic are generally not well accepted by the scientific community, and are rejected by most researchers and scientific theories on the subject.
Carbon-13 (13C) is a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth.
Isotopic labeling is a technique used to track the passage of an isotope through a reaction, metabolic pathway, or cell. The reactant is 'labeled' by replacing specific atoms by their isotope. The reactant is then allowed to undergo the reaction. The position of the isotopes in the products is measured to determine the sequence the isotopic atom followed in the reaction or the cell's metabolic pathway. The nuclides used in isotopic labeling may be stable nuclides or radionuclides. In the latter case, the labeling is called radiolabeling.
In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers are used in many scientific fields.
In chemistry and geology, biomarkers are any suite of complex organic compounds composed of carbon, hydrogen and other elements or heteroatoms such as oxygen, nitrogen and sulfur, which are found in crude oils, bitumen, petroleum source rock and eventually show simplification in molecular structure from the parent organic molecules found in all living organisms. Essentially, they are complex carbon-based molecules derived from formerly living organisms. Each biomarker is quite distinctive when compared to its counterparts, as the time required for organic matter to convert to crude oil is characteristic. Most biomarkers also usually have high molecular mass.
Oleanane is a natural triterpenoid. It is commonly found in woody angiosperms and as a result is often used as an indicator of these plants in the fossil record. It is a member of the oleanoid series, which consists of pentacyclic triterpenoids where all rings are six-membered.
Cholestane is a saturated tetracyclic triterpene. This 27-carbon biomarker is produced by diagenesis of cholesterol and is one of the most abundant biomarkers in the rock record. Presence of cholestane, its derivatives and related chemical compounds in environmental samples is commonly interpreted as an indicator of animal life and/or traces of O2, as animals are known for exclusively producing cholesterol, and thus has been used to draw evolutionary relationships between ancient organisms of unknown phylogenetic origin and modern metazoan taxa. Cholesterol is made in low abundance by other organisms (e.g., rhodophytes, land plants), but because these other organisms produce a variety of sterols it cannot be used as a conclusive indicator of any one taxon. It is often found in analysis of organic compounds in petroleum.
Phytane is the isoprenoid alkane formed when phytol, a constituent of chlorophyll, loses its hydroxyl group. When phytol loses one carbon atom, it yields pristane. Other sources of phytane and pristane have also been proposed than phytol.
Ferruginol is a natural phenol with a terpenoid substructure. Specifically, it is a diterpene of the abietane chemical class, meaning it is characterized by three fused six-membered rings and alkyl functional groups. Ferruginol was first identified in 1939 by Brandt and Neubauer as the main component in the resin of the Miro tree and has since been isolated from other conifer species in the families Cupressaceae and Podocarpaceae. As a biomarker, the presence of ferruginol in fossils, mainly resin, is used to describe the density of these conifers in that particular biosphere throughout time.
Unresolved complex mixture (UCM), or hump, is a feature frequently observed in gas chromatographic (GC) data of crude oils and extracts from organisms exposed to oil.
Biomarkers in analytical chemistry and in environmental science are chemicals, metabolites, susceptibility characteristics, or changes in the body that relate to the exposure of an organism to a chemical. They have the ability to identify if an exposure has occurred, the route of exposure, the pathway of exposure, and the resulting effects of the exposure. The use of biomarkers in exposure studies is also referred to as biomonitoring. When dealing with exposure assessment, there are three types of biomarkers that can be useful, biomarkers of susceptibility, biomarkers of exposure, and biomarkers of effect. Biomarkers of exposure are the most widely used because they can provide information on the route, pathway, and sometimes, even the source of exposure.
Abietane is a diterpene that forms the structural basis for a variety of natural chemical compounds such as abietic acid, carnosic acid, and ferruginol which are collectively known as abietanes or abietane diterpenes.
Okenane, the diagenetic end product of okenone, is a biomarker for Chromatiaceae, the purple sulfur bacteria. These anoxygenic phototrophs use light for energy and sulfide as their electron donor and sulfur source. Discovery of okenane in marine sediments implies a past euxinic environment, where water columns were anoxic and sulfidic. This is potentially tremendously important for reconstructing past oceanic conditions, but so far okenane has only been identified in one Paleoproterozoic rock sample from Northern Australia.
Bisnorhopanes (BNH) are a group of demethylated hopanes found in oil shales across the globe and can be used for understanding depositional conditions of the source rock. The most common member, 28,30-bisnorhopane, can be found in high concentrations in petroleum source rocks, most notably the Monterey Shale, as well as in oil and tar samples. 28,30-Bisnorhopane was first identified in samples from the Monterey Shale Formation in 1985. It occurs in abundance throughout the formation and appears in stratigraphically analogous locations along the California coast. Since its identification and analysis, 28,30-bisnorhopane has been discovered in oil shales around the globe, including lacustrine and offshore deposits of Brazil, silicified shales of the Eocene in Gabon, the Kimmeridge Clay Formation in the North Sea, and in Western Australian oil shales.
Regolith-hosted rare earth element deposits are rare-earth element (REE) ores in decomposed rocks that are formed by intense weathering of REE-rich parental rocks in subtropical areas. In these areas, rocks are intensely broken and decomposed. Then, REEs infiltrate downward with rain water and they are concentrated along a deeper weathered layer beneath the ground surface.
Tetrahymanol is a gammacerane-type membrane lipid first found in the marine ciliate Tetrahymena pyriformis. It was later found in other ciliates, fungi, ferns, and bacteria. After being deposited in sediments that compress into sedimentary rocks over millions of years, tetrahymanol is dehydroxylated into gammacerane. Gammacerane has been interpreted as a proxy for ancient water column stratification.
Sugiol is a phenolic abietane derivative of ferruginol and can be used as a biomarker for specific families of conifers. The presence of sugiol can be used to identify the Cupressaceae s.1., podocarpaceae, and Araucaraiaceae families of conifers. The polar terpenoids are among the most resistant molecules to degradation besides n-alkanes and fatty acids, affording them high viability as biomarkers due to their longevity in the sedimentary record. Significant amounts of sugiol has been detected in fossil wood dated to the Eocene and Miocene periods, as well as a sample of Protopodocarpoxylon dated to the middle Jurassic.
Arborane is a class of pentacyclic triterpene consisting of organic compounds with four 6-membered rings and one 5-membered ring. Arboranes are thought to be derived from arborinols, a class of natural cyclic triterpenoids typically produced by flowering plants. Thus arboranes are used as a biomarker for angiosperms and cordaites. Arborane is a stereoisomer of a compound called fernane, the diagenetic product of fernene and fernenol. Because aborinol and fernenol have different biological sources, the ratio of arborane/fernane in a sample can be used to reconstruct a record for the relative abundances of different plants.
Highly branched isoprenoids (HBIs) are long-chain alkenes produced by a small number of marine diatoms. There are a variety of highly branched isoprenoid structures, but C25 Highly branched isoprenoids containing 1 to 3 double bonds are the most common in the sedimentary record. Highly branched isoprenoids have been used as environmental proxies for sea ice conditions in the Arctic and Antarctic throughout the Holocene, and more recently, are being used to reconstruct more ancient ice records.
