K-Pg mass extinction
In 1980, Luis and Walter Alvarez, Frank Asaro, and Helen Michels discovered, across the world, a spike in the concentration of iridium within the sedimentary layer at the K–Pg boundary. These researchers hypothesized that this iridium spike was caused by an asteroid impact that resulted in the K–Pg mass extinction. In the photo, the iridium layer is the light band.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, The Biodiversity Crisis. October 17, 2013."
http://cnx.org/content/m44892/latest/Figure_47_01_05.png
OpenStax CNX
CC BY 3.0.
