The pattern in the fossil record which supports the idea of a mass extinction event is the sharp decrease in biodiversity in rock layers.
A mass extinction event is one which in which a large number of species of organisms die off due to natural or artificial causes.
A mass extinction events is concluded to have killed the dinosaurs and other species, in part as a result of an asteroid striking the planet.
The evidence for this in fossils records is that the lower, older rock layers contains a great diversity of fossil life forms, while the younger layer immediately above is contains few organisms in comparison.
Therefore, the sharp decrease in biodiversity in rock layers provides evidence for a mass extinction event.
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