Answered: The Cretaceous–Paleogene (K–Pg)…

Applications and Investigations in Earth Science (9th Edition)

9th Edition

ISBN:9780134746241

Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Chapter1: The Study Of Minerals

Section: Chapter Questions

Problem 1LR

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The Cretaceous–Paleogene (K–Pg) extinction was one of the largest mass extinctions in Earth’s history, as roughly three-quarters of all plant and animal species perished. The extinction event marked the end the Cretaceous period and the beginning of the Paleogene period 66 million years ago. Geologically, this transitional period is represented by a layer of rock called the K–Pg boundary (in the photo, the handle of the hammer points to the K–Pg layer).

In the late 1970s, Walter and Luis Alvarez (a father–son duo) investigated the chemical composition of the K–Pg boundary layer in regions of Denmark and Italy. They discovered that the boundary layer contained unusually high levels of iridium, an element rare in Earth’s crust but abundant in space rocks.

The following table depicts the average abundance of iridium (in parts per billion) in rock samples at the K–Pg boundary layer, as well as at depths (in meters) above and below the boundary layer.

From which period is a rock at +1.2 m depth?

Paleogene

Cretaceous