Using the GeoRef database in Dialog Select on the Internet, I did a subject search for Chicxulub Crater, specifying articles in English, without a restriction on year. There were a total of forty seven hits, and the last, and therefore, oldest one was an article by Alan R. Hildebrand and associates, called Chicxulub Crater: A Possible Cretaceous/Tertiary Boundary Impact Crater on the Yucatan Peninsula, Mexico. The citation is as follows:
Hildebrand, Alan R.; Penfield, Glen T.; Kring, David A.; Pilkington, Mark; Camargo Z.; Jacobsen, Stein B.; Boyton, William V. 1991. Chicxulub Crater: A Possible Cretaceous/Tertiary Boundary Impact Crater on the Yucatan Peninsula, Mexico. Geology (Boulder), Volume 19, Number 9, Page 867 871.
Since this paper was the oldest one found in the database, it was believed to be a key paper on the subject. This was later confirmed by consultation with someone who is quite knowledgeable in scientific matters. Key papers are important because they let you find the early unpublished stages of research activity, "follow the history or methodology of an idea from its first communication to the present, locating current research based on earlier published works or findings, create a list of experts within a field of research, and analyze the impact of published research" (Katz 1987, 9).
Until 65 million years ago dinosaurs lived on this planet, but within a short period they were extinct. Not only did the dinosaurs suddenly disappear, an examination of a variety of fossils show that 70% of all living species, both plant and animal, disappeared along with the dinosaurs. There was a mass extinction, with the death of most living creatures. The death of the dinosaurs has always been one of the greatest mysteries to face scientists and many have given suggestions for their disappearance.
A very controversial theory has suggested that the destruction of living species 65 million years ago was triggered by the collision of a huge asteroid with the Earth, which would have created a crater at least 150 km wide. An impact of this magnitude would have caused a tremendous amount of energy within a short time, along with acid rain, incineration, greenhouse warming, and cold darkness a deadly combination. Evidence for such an occurrence has been deposits of "iridium-rich clay found at the boundary of the Cretaceous and Tertiary deposits known as the K/T Boundary" (Hildebrand 1991,868).
During an aerial survey of the region in 1978, Pemex, Mexico's national oil company located what it believed was a buried impact crater nearing 180 km. in diameter close to the town of Chicxulub. For unknown reasons, this information was never released to the scientists actively looking for such a site, nor to the scientific world until 1990. It was announced in 1981 at a petroleum geology conference, but the information was not passed along to the K/T Boundary people. By 1991, Alan Hildebrand and his associates from the University of Arizona, Harvard University, and the Geological Survey of Canada had concluded that,
The Chicxulub Crater is the largest probable impact crater on Earth. Its position and target rock composition satisfy many of the characteristics required for the K/T crater, and it may have a K/T boundary age. This impact may have caused the K/T extinctions (Hildebrand 1991,871).
Since 1991, Alan Hildebrand has continued to work with others in the field on the mystery surrounding the Chicxulub Crater. Many other scientists have also used their research to begin or extend experiments of their own in this very important area. To find out how often Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico has been cited by others doing research, one can use SCI or SciSearch. Its distinction is that it includes all the cited references (footnotes and bibliographies) for each article it indexes. Originally, when this was done using the version of Dialog Select on the Internet, only forty four articles were found to have cited the 1991 paper, most of which were obviously from the field of microbiology. These results seemed incomprehensible because only one paper was on topic. The process was started all over again using Dialog at the local university, and the numbers changed dramatically, this time providing 120 citations. (Although the 1991 paper was a seminal piece of work, it has not been identified as a SCI Citation Classic, nor a SCI Research Front.)
By retracing the search steps leading to the incorrect answer, it was realized that Dialog Select gives Instructions to use the first three letters of an author's first name, rather than the initials. Having used the initials A.R., I tried again, and the numbers went from 44 to 120. Why those incorrect instructions were posted on the website is unknown, but they caused me to retrieve a batch of citations that were off topic, and obviously not in any way connected to Alan R. Hildebrand. With the new results in hand, the next step was to find out how many of the citing articles were subject related.
By looking at the abstracts for all of the 120 citing articles, there was no question that each of them was subject related and on topic. However, under certain circumstances a cited reference search might yield articles that are off topic or of little use. Authors might use one small aspect of a study in their own work, something that relates to the study at hand, or simply referring to it in passing, but must cite the reference. For example, a researcher may be studying specialized stratigraphy in the Southern Hemisphere, and refer to the area around Chicxulub, Mexico, while using some findings from the work done by Hildebrand and associates. Of course, the paper has nothing to do with asteroids hitting Earth millions of years ago, but would undoubtedly come up in a SciSearch. The citing of articles of a tertiary manner is unavoidable, and does sometimes result in the retrieval of unwanted materials.
In addition, there is the problem of padding bibliographies within certain fields. This means that certain authors will cite papers in their references although they have not actually read or used the concepts in them. It is sometimes done so that an article will look more academic or prestigious by citing the works of important authors, or having a large number of citations. The only other disadvantage of using SCI over a conventional subject index is the cost. When compared with other databases, it is extremely expensive and should be used with consideration given to the financial expenditure. As previously stated, those articles citing Hildebrand's 1991 paper were on topic. What follows is a small sample of the titles to prove the point.
1. Size and morphology of the Chicxulub Impact Crater.
2. Re Os isotope systematics as a diagnostic tool for the study of impact craters and distal ejecta.
3. Extraterrestrial impact events: the record in the rocks and the stratigraphic column.
4. Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact.
5. When the sky fell on our heads identification and interpretation of impact products in the sedimentary record.
6. Magnesioferrite spinel in Cretaceous/Tertiary Boundary sediments of the Pacific Basin remnants of hot, early ejecta from the Chicxulub impact.
7. Impact of meteorites.
8. Models and causes of mass extinction.
9. Impact a natural hazard in planetary evolution.
10. Impact winter and the Cretaceous/Tertiary extinctions results of a Chicxulub asteroid model.
11. Yucatan Karst features and the size of Chicxulub Crater.
12. Cretaceous Tertiary (Chicxulub) impact angle and its consequences.
13. Chicxulub, the ideal crater.
14. Target earth: evidence for large scale impact events.
15. Did the European dinosaurs disappear before the K/T event? Magnetostratigraphic evidence.
Assessing the quality of scientific publications has long been a major problem, and the academic community had no choice but to view prolific writers as outputting quality work; there was the age old struggle between quantity and quality. That was until the introduction of the Science Citation Index (SCI), a reliable tool to measure the significance of individual scientists' contributions. Citation indexing is a method of organizing documents in a way that overcomes many of the shortcomings of the more traditional indexing methods. SCI has listed all bibliographic references appearing in an increasingly large number of journals, allowing the number of citations an individual receives to be tabulated and used as an indicator of the relative scientific significance or quality of that individual's publications.
The primary advantage of citation indexing is that it identifies relationships between academic publications that are often overlooked in a subject index. A second important advantage is that the compilation of citation indexes is especially well suited to the use of machine indexing methods that do not require indexers who are subject specialists (Katz 1987,171). Furthermore, citations, which are bibliographic descriptions of documents, tend to bring together material that would never be collated by the usual subject indexing because they "are not vulnerable to scientific and technological obsolescence as are the terms used in subject indexes" (Katz 1987,172). Whereas a traditional topic search is dependent on your knowledge of the field's vocabulary and on how well you formulate your search statement, a cited reference search leads you to relevant data through the experts themselves. Since this type of search is not language dependent, it will reveal changes in terminology and phrases being used in your area of research (Katz 1987,174).
Studies have shown that a citation search will yield relevant results that could not be found by conducting a topic search. It overrides the need to have indexers provide exact terms of controlled vocabulary to connect papers by retrieving related articles via cited reference searching rather than subject searching which has its pitfalls. For instance, a search for citations to journal articles allows one to perform more comprehensive searches of the journal literature, and retrieve all the data relevant to a particular subject, despite how limited your initial information is. You may know the name of an important researcher who published a work several years ago, but are not sure how to find current research on that same topic. By using the author's name, a cited reference search can lead you to more recent papers it is a very powerful tool which allows you to move forward in time. SCI can also be helpful to the scholar, who would like to be aware of possible criticisms of his or her work made by colleagues in the field. This can be done by discovering who is referencing the information and how it is being used to support current research. The citation index makes this possible.
Katz, William A. 1987. Introduction to References Work. New York. McGraw Hill Book Company.
Citation Data is Subtle Stuff a Primer on Evaluating Scientist's Performance. 1987. Scientist 1(10): 9, p.6.