An asteroid impact 65.5 million years ago may have caused a mass extinction event that resulted in the simultaneous loss of many lineages from Earth. This event is marked by a unique global rock layer known as the K-Pg boundary, which formed 65.5 million years ago and implies an abrupt transition in the fossil record at the time of mass extinction.

1. Chapter 16
Evidence of Evolution
Section 16.9

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16.9 Reflections of a Distant Past
• An asteroid impact may have caused a mass extinction
65.5 million years ago
– Resulted in a simultaneous loss of many lineages from Earth

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Reflections of a Distant Past (cont’d.)
• K-Pg boundary sequence (formerly known as K-T
boundary)
– A unique rock layer
– Formed worldwide 65.5 million years ago
– Marks an abrupt transition in the fossil record
– Implies a mass extinction

4. © Cengage Learning 2015
Reflections of a Distant Past (cont’d.)
Figure 16.18 The K–Pg boundary
sequence, an unusual, worldwide
sedimentary rock formation that formed 66
million years ago