A Trilobite (Courtesy commons.Wikimedia.org)
"...Abrupt, even catastrophic, regional to global mass mortalities and extinctions (bioevents) are predictable and commonly observed in Phanerozoic strata...."
 
 –   Erle G. Kauffmann, Palaoios, vol. 2, no. 6, 1987.
 
 
For the CCC geologic model's explanation
for this, see:
The CCC Model and Its Geologic Implications