2.3 Mass Extinctions (1981-2001) and (2001-2010)

Initial Study in 2002

There are five known major mass extinctions on earth. The extinction of dinosaurs occurred in the most recent one - the K-T extinction, which was 65 million years ago.

Our first study of the case is reported in Chen et al. (2002), based on a Pathfinder network without time slicing as the base map and annual citation increments growing along the third dimension.

Revisited in 2006

There were over 80 theories of the K-T extinction. One of the most compeling ones is the big purple circle in the following timeline visualization, followed by the green stream of studies until the conclusive evidence was found in early 1990s. The footprint of the research community subsequently switched to the orange stream of studies on the top of the chart, driven by an application of the same theory, or at least, the same way of thinking, to another mass extinction of 250 million years ago.

The latest burst term captured by this analysis was the phrase Permian-Triassic boundary, referring to the PT mass extinction 250 million years ago.

The general movement of the scholarly inquiry was confirmed several years later in a systematic review of the topic by domain experts.

Revisited in 2010

We revisited the research area again in 2011. We are particularly interested in the development of the orange stream identified in the 2006 analysis. So we picked it up from where we stopped last time. The viewing window this time ranges from 2001 till 2010. As shown in the following visualization, Becker (2001) is a landmark article in the major cluster #11, labeled as - reassuringly - Permian-Triassic boundary. Cluster #15, shown in the blue circle, consists of mostly red links, indicating that it must be where the forefront of the research was at the time. Two papers are mostly responsible for the formation of the cluster. One of them is by French and Koeberl (2010), which is a review paper, entitled "The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why."

What makes the French and Koeberl (2010) even more interesting is what we found next. In their background section, French and Koeberl (2010) described in remarkably similar terms of what we observed in our 2006 study. I color the matching phrases below to highlight the similarity.

French and Koeberl (2010), page 152:

Since the establishment of a firm connection between the later K-T extinction and a major impact event (Alvarez et al., 1980), numerous workers have searched for evidence of a similar connection between another large impact event and the Permian extinctions.

Chen (2006), page 369:

Encouraged by the successful puzzle-solving experience, many scientists appear to have adapted the same approach to solve a different puzzle - by applying the impact theory to an earlier mass extinction.

As the designer of CiteSpace, I have at least two good reasons to be pleased about two independently made observations of this level of similarity. First, we are not a domain expert, not even a beginner to the domain, and yet we were able to make an observation of the dynamics of the domain by analyzing patterns emerged from the literature. Furthermore, the observation was evidently consistent with what domain experts made based on their knowledge of the domain. Second, we made our observation in our paper published in 2006, which is a few years ahead of 2010. This is an encouraging fact that one can repeatedly apply the tool to the literature and make your own observations.

The following diagram is a roadmap of the field made by Wignall, a leading expert in the field. As a belief map of the domain knowledge, each domain expert has one of their own. Each beginner or a new comer may hope to get one for themselves. This is an important area of interest. We will return to this topic later on.

References

• Chen, C., Cribbin, T., Macredie, R. and Morar, S. (2002) Visualizing and tracking the growth of competing paradigms: Two case studies.Journal of the American Society for Information Science and Technology, 53 (8), 678-689.
• Chen, C. (2006) CiteSpace II: Detecting and visualizing emerging trends and transient patterns in scientific literature. Journal of the American Society for Information Science and Technology, 57(3), 359-377.
• French, B. M., Koeberl, C. (2010) The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why. EARTH-SCIENCE REVIEWS, 98, 123-170.
• Wignall, P. B. (2007) The end-Permian mass extinction - how bad did it get? Geobiology, 5(4), 303-309. 10.1111/j.1472-4669.2007.00130.x