Tracing Competing Paradigms - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 209

Fig. 6.7 The location of the Chicxulub crater

in Siberia, dated only 28.8 million years old, would be too young. Alvarez and his
colleagues suggested that there was a 2/3 probability that the impact site was in the
ocean. If that was the case, we would not be able to find the crater because evidence
from the ocean of that age had long gone. Nevertheless, searching for the impact
crater had become a crucial line of research. A breakthrough came in 1991 when
Alan Hildebrand linked the Chicxulub crater to the KT impact.
The Chicxulub crater is a 110-mile (180-km) structure, completely buried under
the Yucatan Peninsula in Mexico (See Fig. 6.7 ). In 1950s, the gravity abnormality
of the Chicxulub crater attracted the Mexican National Oil Company (PEMEX)
searching for oil fields, but the crater remained its low profile to the community of
mass extinction research until Alan Hildebrand's discovery.
Hildebrand's 1991 paper is one of the most highly cited articles in the KT impact
cluster (Hildebrand et al. 1991 ). Figure 6.8 shows the gravity field and magnetic
field of the Chicxulub crater.
Since the impact theory was conceived, its catastrophism point of view has
received strong resistance, especially from paleontologists who held a gradualism
viewpoint. The impact theory, its interpretations of evidence, and the validity of
evidence have been all under scrutiny.
In Walter Alvarez's topic, Gerta Keller was regarded as the number one opponent
of the impact theory (Alvarez 1997 ). A number of Keller's several papers appeared
in the KT impact cluster, including their 1993 paper, in which they challenged the
available evidence of impact-generated tsunami deposits.
The presence of articles from a leading opponent to the impact theory right
in the center of this cluster has led to new insights into visualizing competing
paradigms. Co-citations not only brought supportive articles together into the same