Putting the K-Pg in Chicxulub K-Pg Impact Crater Expedition

The official name of this expedition is “Chicxulub K-Pg Impact Crater.” Hopefully by now you know what “Chicxulub” and “impact crater” mean, but you may not know what “K-Pg” means. If that is the case, then today is your lucky day.

If you are not a geologist or a paleontologist, then “K-Pg” may sound like the hip hop nickname of a rapper in the late 1980’s, but it actually is the abbreviation for the Cretaceous-Paleogene Boundary. This is a boundary in geologic time. It marks the dividing line between the Cretaceous period and the Paleogene period, as well as the dividing line between the Mesozoic Era and Cenozoic Era. Boundaries in geologic time indicate that some enormous change happened at that time, like a mass extinction.

Geologic time_kleiner.jpg
Geologic Time Scale

The K-Pg boundary is also a physical boundary you can see in the stratigraphy (the rock layers) around the world. It is a layer that contains a lot of ash and iridium (an element that is rare on Earth and usually indicates an asteroid or meteorite impact).

In this photo, you can see one of our science party, David Kring, pointing at the K-Pg boundary in a rock outcrop in Colorado.

As you may have already figured out, the K-Pg boundary is integrally linked to the Chicxulub asteroid impact.  The impact created the layer of ash, iridium, and other debris by spewing rock and asteroid bits around the world. The impact also caused the mass extinction that drastically changed the Earth.  “Chicxulub Impact” and “K-Pg boundary” are so linked together that they are almost synonymous.

PS: It’s called “the K-Pg Boundary” and not “the C-Pg Boundary,” because “C” was already claimed as an abbreviation for the Cambrian Period. The Cretaceous Period was given the abbreviation “K” from the German word for chalk, Kreide.

Just to be more confusing, the K-Pg boundary is also the boundary formerly known as “the K-T boundary.” “K-T” stands for Cretaceous-Tertiary. The Tertiary period used to be the name of the period that followed the Cretaceous, but not too long ago, the International Commission of Stratigraphy decided to sack the Tertiary period and replace it with the Paleogene and Neogene periods. So we’re not supposed to say K-T boundary anymore, though the change was recent enough that there are a lot of places where you will still see that term used.

By Kevin Kurtz

Images used above are from the Center for Lunar Science and Exploration website (http://www.lpi.usra.edu/exploration/training/resources/?view=illustrations), which includes many images and other resources about the Chicxulub impact and meteorites in general that are free to use for educators.


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