Walter Alvarez

Walter Alvarez is an American geologist who, with his father Luis Alvarez and other collaborators, proposed that an asteroid impact caused the end-Cretaceous mass extinction.

Luis Alvarez: Luis Alvarez was an American physicist who shared the 1968 Nobel Prize in Physics and co-proposed the impact explanation for the K–Pg extinction. His suggestion to test iridium in the boundary clay launched the collaboration with his son.
Iridium anomaly: An iridium anomaly is an unusually high concentration of the rare element iridium in a geological layer. The anomaly in the K–Pg boundary clay provided the hypothesis’s initial clue.
Gubbio: Gubbio is an Italian town near the Bottaccione Gorge, where a continuous sequence of Cretaceous and Paleogene rocks is exposed. The limestone sequence near Gubbio supplied the boundary clay that prompted Alvarez’s investigation.
Alvarez hypothesis: The Alvarez hypothesis proposes that a large asteroid impact caused the Cretaceous–Paleogene mass extinction. Walter Alvarez co-developed this explanation from geological evidence and trace-element measurements.
Frank Asaro: Frank Asaro was an American nuclear chemist who developed neutron-activation methods used to measure trace elements in geological samples. His measurements established the unusually high iridium concentration in the boundary clay.
K–Pg boundary: The K–Pg boundary is the geological interface marking the transition from the Cretaceous Period to the Paleogene Period. Alvarez and colleagues measured iridium in clay from this worldwide boundary layer.
Bottaccione Gorge: Bottaccione Gorge is a ravine near Gubbio, Italy, exposing marine rocks that record the K–Pg boundary. Walter Alvarez studied its strata while investigating changes in the geological record.
Chicxulub impact: The Chicxulub impact was the collision of a large asteroid with Earth about 66 million years ago, creating the Chicxulub crater. The impact supplied the physical event that the Alvarez hypothesis had predicted.
Helen Michel: Helen Michel is an American nuclear chemist known for applying neutron activation analysis to archaeological and geological materials. She helped analyze the boundary clay samples that supplied key evidence for the hypothesis.
Chicxulub crater: Chicxulub crater is a large buried impact structure beneath Mexico’s Yucatán Peninsula, formed about 66 million years ago. Its discovery identified the likely impact site predicted by the hypothesis.

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