Organic geochemistry – A retrospective of its ﬁrst 70 years q

Organic geochemistry had its origin in the early part of the 20th century when organic chemists and geologists realized that detailed information on the organic materials in sediments and rocks was scientiﬁcally interesting and of practical importance. The generally acknowledged ‘‘father’’ of organic geochemistry is Alfred E. Treibs (1899–1983), who discovered and described, in 1936, porphyrin pigments in shale, coal, and crude oil, and traced the source of these molecules to their biological precursors. Thus, the year 1936 marks the beginning of organic geochemistry. However, formal organization of organic geochemistry dates from 1959 when the Organic Geochemistry Division (OGD) of The Geochemical Society was founded in the United States, followed 22 years later (1981) by the establishment of the European Association of Organic Geochemists (EAOG). Organic geochemistry (1) has its own journal, Organic Geochemistry (beginning in 1979) which, since 1988, is the oﬃcial journal of the EAOG, (2) convenes two major conferences [International Meeting on Organic Geochemistry (IMOG), since 1962, and Gordon Research Conferences on Organic Geochemistry (GRC), since 1968] in alternate years, and (3) is the subject matter of several textbooks. Organic geochemistry is now a widely recognized geoscience in which organic chemistry has contributed signiﬁcantly not only to geology (i.e., petroleum geochemistry, molecular stratigraphy) and biology (i.e., biogeochemistry), but also to other disciplines, such as chemical oceanography, environmental science, hydrology, biochemical ecology, archaeology, and cosmochemistry.


Introduction
Organic geochemistry is a modern geoscience that results from the amalgamation of many aspects from the two fundamental, but disparate, scientific disciplines of geology and organic chemistry. The latter half of the 18th century saw the independent rise of each of these basic disciplines. Geology began in the 50 years between 1775 and 1825 with the musings of James Hutton (see McIntyre, 1963); organic chemistry, during approximately the same time interval, grew out of the recognition of the basic difference between organic and inorganic chemical compounds -organic compounds always contain carbon (see Noller, 1957). Geology and organic chemistry continued to evolve independently until the early part of the 20th century when geologists realized the scientific and practical importance of organic matter in rocks, and organic chemists discovered that rocks contain an abundance of organic compounds of fundamental and applied interest. The purpose of this paper is to (1) update information about the formal organization of organic geochemistry, (2) summarize the lives of early practitioners in the field, (3) gauge the content of the subject matter, and (4) acknowledge those who organized organic geochemistry and those who have helped sustain the field through their editorships of Organic Geochemistry. Fig. 1 shows a timeline of events in the development of the history of organic geochemistry.

Origins and awards
Two individuals can be identified who successfully merged geology and organic chemistry in the 1930s. From the geologic side, Parker D. Trask ( Fig. 2A) related the organic materials in sediments (Trask, 1932) and sedimentary rocks (Trask and Patnode, 1942) to an understanding of the source beds of petroleum. From the organic chemistry side, Alfred E. Treibs (Fig. 2B) discovered organic (porphyrin) pigments in shale, crude oil, and coal (Treibs, 1936), and demonstrated that these pigments were degradation products from biological sub-stances (chlorophyll and hemin), thus linking geomolecules to biomolecules. These men were contemporaries, both born in 1899, but it is unlikely that their paths ever crossed.

Parker D. Trask
Parker Trask ( Fig. 2A) came from New England in the United States, and was educated in California, obtaining an advanced degree in geology from the University of California at Berkeley. From 1926 to 1931 he was a research associate with the American Petroleum Institute (API), working on studies related to petroleum source rocks. In 1931 the source-bed project became a joint undertaking with the API and the U.S. Geological Survey (USGS), and Trask became a USGS employee, a connection he retained full time for 15 years and part time thereafter until his death in 1961. The joint API/USGS project, which he led, continued for 10 years during which time the chemical and physical properties of more than 25,000 samples from many geological formations from most parts of the United States were studied. The goal was to determine possible relationships between these samples and oil reservoirs in a search for clues to the recognition of true petroleum source beds. During   much of his later life (after 1941) Trask devoted his attention to engineering geology, and he is better remembered as an engineering geologist than an organic geochemist (Bailey, 1962;Gilluly, 1963). He probably did not even consider himself an organic geochemist, and perhaps did not even know that he was, in essence, an early practitioner of organic geochemistry on a grand scale, emphasizing the ''geo'' aspects of the subject.

Alfred E. Treibs
In contrast to Trask, Alfred Treibs ( Fig. 2B) was well recognized during his lifetime as an organic geochemist. His scientific research on porphyrin pigments in various geological materials, spanning almost five decades, set the stage and the standard for the new geoscience of organic geochemistry. His pioneering body of work is internationally recognized, and he was acclaimed and honored on his 80th birthday in 1979 by the symposium entitled ''The Impact of the TreibsÕ Porphyrin Concept on the Modern Organic Geochemistry'' (Prashnowsky, 1980). In 1999, 16 years after his death, a symposium was ''Dedicated to the Memory of Alfred Treibs, the Father of Organic Geochemistry on the 100th Anniversary of his Birthday'' (Prashnowsky, 2002).
Treibs was born in the German village of Idar-Oberstein; his home is now marked with a bronze plaque [GEBURTSHAUS VON PROF. DR. ALFRED TREIBS (1899-1983) BEGRÜ NDER DER ORGANISCHEN GEOCHEMIE]. He studied chemistry in Aachen and later in Munich where he obtained advanced academic degrees at the Technical University (TU). He continued on the staff at the TU for most of his career, except for the time from 1936 to 1945 when he worked at Wacker-Chemie, an industrial research institute. During his 50-year association with the TU, he was involved with research on porphyrins, first as a student supervised by Han Fischer (awarded a Nobel Prize for the utilization of physico-chemical methods applied to pyrroles, the basic structures of porphyrins), and later as FischerÕs colleague, as a research leader, and as a teacher. At the TU, Treibs laid the foundations of the science of Organic Geochemistry with his fundamental research leading to an understanding of the significance of porphyrin pigments in shale, oil, and coal (Treibs, 1936). With the recognition of Treibs as the ''father'' of organic geochemistry, the date 1936 represents the begin-ning of the geoscience of organic geochemistry, 70 years ago. A tribute to Treibs has been provided by Seifert (1977), who was one of TreibsÕ many students.

Awards
In recognition of the pioneering work of Alfred Treibs, an award was established in his name. The Alfred E. Treibs Award (consisting of a Medal and Certificate) is given for ''outstanding contributions to Organic Geochemistry'', and was presented as an honorary award to A.E. Treibs in 1979. In the same year, the first designated recipient was G.T. (Ted) Philippi ( Fig. 2C) for his pioneering work in petroleum geochemistry, a major part of organic geochemistry. Much of his research was conducted from 1936 to 1968 in various laboratories of Shell Oil Company. His publications, though not numerous, were recognized by the organic geochemical community as conceptually important and very stimulating. Appearing late in his professional career, after a lifetime of experience, his publications, beginning about 1957, dealt with (1) the chemical recognition of petroleum source rocks, (2) the importance of subsurface temperatures on the formation and composition of petroleum, (3) the roles of marine and terrestrial plants as the ultimate sources of petroleum, and (4) the nature and extent of bacterial affects on petroleum. His active life as a petroleum geochemist continued unabated after his retirement in 1968, and many of his publications appeared after that date. His early contributions to petroleum geochemistry have been outstanding.
From 1979 through 2002, 17 organic geochemists have received the Treibs Award (Kvenvolden, 2002). Since 2002 this award has been presented to Roger Summons (2003), Eric Galimov (2004), and Jaap Sinninghe Damsté (2005). Two other awards are given to recognize organic geochemists -the Pieter A. Schenck Award and the Australian Organic Geochemistry Medal. The Schenck Award is given every second year to a scientist under 35 years of age who has made a major contribution to any specific area of organic geochemistry or related field.

Organizations and conferences
Organic geochemistry was formally organized and recognized as a geoscience about 30 years after Treibs and Trask set the stage (Fig. 1). In 1959 Bart Nagy ( After OGD was formally organized in 1959, two series of conferences have been devoted specifically to organic geochemistry for more than 40 years ( GRCs on Organic Geochemistry have been held every other year at Holderness School, New Hampshire, since 1968. The 1968 conference was titled ''Organic Geochemistry'', but in 1970 and 1972 the conferences were titled ''Geochemistry'', although the main topic of discussion was organic geochemistry. From 1974 to the present, the name ''Organic Geochemistry'' has been used to identify the subject matter of these conferences. The idea of a GRC on organic geochemistry seems to have originated in 1963 with a conference entitled ''Origin of Petroleum''. For the next six years, GRCs were convened and dealt with broad issues in geochemistry, including organic geochemistry, but it was not until 1968 and thereafter that GRCs focused specifically on organic geochemistry. A tabulation of GRCs (from 1968 to 2002) is given in Kvenvolden (2002). One GRC has met since in 2004 with S. Wakeham as Chairperson.

The journal Organic Geochemistry
Responding to the proliferation of technical papers addressing organic geochemical topics, Irving Breger established the journal Organic Geochemistry Organic Geochemistry has been established in response to the need for a specialized medium for the publication of research in this highly interdisciplinary field. At present papers concerned with interrelated fields such as organic chemistry, inorganic chemistry, geology, mineralogy, biogeochemistry, oceanography, hydrology, atmospherics and extraterrestrial subjects are published in many scattered journals. It is intended that Organic Geochemistry serve as a medium for the publication of reports on all phases of geochemistry in which organic substances play a role. Interpretation of this policy will be liberal to permit the broadest possible exchange of ideas. Among others, papers related to crude oils, coals, natural gas and shales and their associated substances will be welcome, as will reports of studies on the roles of organic substances in the geochemical cycles of various elements. Reports of paleontological and coal petrographic studies will be considered favorably if they are geochemically oriented. Letters to the Editor, relevant news and book reviews will be published. Individual issues of Organic Geochemistry may be devoted to papers at Symposia.
This statement became the Aims and Scope of the journal through v. 20, n. 3 (1993); in the next issue [v. 20, n. 4 (1993)] the Aims and Scope were expanded and have appeared in most issues of the journal to the present. The expanded version can be found at the frontmatter of this issue of Organic Geochemistry. In addition to the major points of the original statement, the current version includes several more specific aspects of organic geochemistry, such as molecular and isotope geochemistry (including compound-specific isotope techniques), environmental geochemistry, organic matter in marine and non-marine sediments, organicrich rocks and soils, archaeological chemistry, biogeochemical ecology, biomolecular paleontology, and molecular stratigraphy. The journal seeks papers covering the full range of research activities in organic geochemistry. Earl W. Baker assumed editorship of the journal in 1983 with v. 5, n. 1 (1983). Also this issue noted the journalÕs official affiliation with EAOG. With v. 12, n. 1 (1988) Organic Geochemistry became ''The Official Journal of EAOG'' with co-editors Earl Baker and Pieter Schenck. To date seven individuals have served as Editors of Organic Geochemistry (Fig. 4).

Textbooks in Organic Geochemistry
In addition to the journal Organic Geochemistry, several books and compilations of papers have been prepared which serve as textbooks on the subject. Table 1 lists the Proceedings of IMOG. Each of these 21 (as of 2005) compilations of papers is assembled under the title ''Advances in Organic Geochemistry'' and presents an up-to-date view of organic geochemistry as of the date of each IMOG conference. Examples of textbooks containing  1197-1634 (2004) papers in organic geochemistry by many different authors are listed in Table 2, and textbooks in which the entire content was prepared by one to three authors are listed in Table 3. These textbooks range in subject matter from general organic geochemistry to specialties such as petroleum geochemistry and the organic geochemistry of non-marine sediments, oil shales, and carbonate rocks.   Table 3 Examples of Organic Geochemistry textbooks in which the content has been prepared by the listed textbook authors Swain, F.G., 1970. Non-marine Organic Geochemistry. Cambridge University Press, UK, 445p Tissot, B.F., Welte, D.H., 1978. Petroleum Formation and Occurrence. Springer-Verlag, Germany, 538p Hunt, J.M., 1979. Petroleum Geochemistry and Geology. Freeman, USA, 617p Waples, D., 1981. Organic Geochemistry for Exploration Geologists. Burgess, USA, 151p Tissot, B.F., Welte, D.H., 1984. Petroleum Formation and Occurrence. second ed. Springer-Verlag, Germany, 699p Philp, R.P., 1985. Fossil Fuel Biomarkers -Applications and Spectra. Elsevier, The Netherlands, 294p Waples, D.W., 1985 Table 4 Organic Geochemistry Division, Best Paper Award Winners

Content
Organic geochemistry is highly interdisciplinary, as outlined above in the Aims and Scope of its journal Organic Geochemistry. An understanding of the breadth and depth of the subject matter can be gained by perusing the numerous papers within each volume (Table 1) published for the twenty-one IMOG conferences that have been held since 1962. Also the textbooks in Tables 2 and 3 contain a variety of papers on subjects dealing with the multiple aspects of organic geochemistry.
Another way to judge the content of this field is to review the published papers that have been selected by committee as Best Papers and Best Student Papers in Organic Geochemistry. To date, 32 Best Paper Awards and 4 Best Student Paper Awards have been presented. Best Papers were first selected starting in 1971 and have been identified every year (except 1988) thereafter until 1998. The 32 Best Papers have been organized here under four categories (Table 4), although some papers could fit under more than one category: Molecular Organic Geochemistry (8 papers); Biogeochemistry (7 papers); Petroleum Geochemistry (10 papers); and Miscellaneous (7 papers). Nineteen of these papers were published in Geochimica et Cosmochimica Acta (GCA, 1974(GCA, -1986. The papers classified under Molecular Organic Geochemistry deal with the discovery and structural determination of several classes of organic molecules found in geological materials. These molecules include di-, tri-, and tetraterpenoid hydrocarbons, aryl isoprenoid hydrocarbons, steranes, carboxylic and amino acids, and sulfurcontaining lipids. In addition, the radiocarbon ages of individual organic compounds have been measured. Biogeochemistry papers are concerned mainly with organic geochemical processes mediated by organisms. For example, papers address the biogeochemistry of lacustrine and marine sediments, lipid cycling, microbial generation of methane, including the use of carbon and hydrogen isotopes, and palaeoenvironmental implications of organic sulfur compounds. The category Petroleum Geochemistry has papers on both bacterial and thermal processes as applied to petroleum occurrence, including studies of isomerization and aromatization of petroleum molecules during basin development. Organic molecules such as steranes, terpanes, and monoaromatic and isoprenoid hydrocarbons are used in the identification of petroleum source rocks, in oil-rock correlations, in assessment of organic matter maturity, and in understanding the origin and migration of petroleum. Papers in the Miscellaneous category treat the geochemistry of bulk organic carbon (kerogen) and include thermal alteration experiments. The four Best Student Papers were identified for the years 1994-1998, and they also reflect some of the content of organic geochemistry (Table 5). Thus, the numerous publications in the IMOG conference proceedings (Table 1), in organic geochemical textbooks (Tables 2 and 3), in GCA, Organic Geochemistry, specialty journals, such as Chemical Geology, Applied Geochemistry, Marine Chemistry, Marine and Petroleum Geology, Bulletin of the American Association of Petroleum Geologists, Environmental Science and Technology, [notably the Best Papers (Table 4) and the Best Student Papers (Table 5)], and general journals, such as Science and Nature, attest to the rich content of the field of organic geochemistry.

Summary
In 70 years, organic geochemistry, an amalgamation of aspects of organic chemistry and geology, has become a mature and widely recognized geoscience. The beginnings can be traced back to the early part of the 20th century when Alfred E. Treibs, an organic chemist, turned his attention to geological materials and discovered the presence of significant organic molecules in shale, coal, and crude oil. Not only did he find complex organic molecules but, perhaps more important, he traced the source of these molecules to their biological precursors. For his visionary and pioneering work, he is generally regarded as the ''father'' of organic geochemistry. Formal recognition of organic geochemistry came about in 1959, when an organization was established to promote organic geochemical research, and conferences focusing on organic geochemical topics have been convened and have met regularly since 1962. Because of the proliferation of scientific papers on organic geochemistry, a need was identified for a journal, and Organic Geochemistry was founded in 1977. Outstanding contributions to the subject have been acknowledged with the presentation of various awards starting two years after the journal was founded. Organic geochemistry is a highly interdisciplinary field, comprising fundamental and applied research, and it is now an important component of many studies in geology and in other fields such as oceanography, hydrology, archaeology, and cosmochemistry.