What is the Cretaceous-Paleogene boundary iridium layer?

The Cretaceous-Paleogene boundary iridium layer is a thin band of sedimentary rock marking the major geological transition between the Mesozoic and Cenozoic eras 66 million years ago. This stratum contains unusually high levels of the rare platinum-group metal iridium compared to the Earth's crust. Discovered by Luis and Walter Alvarez in 1980, this iridium anomaly serves as crucial physical evidence that a massive extraterrestrial asteroid impact triggered the mass extinction event that wiped out the non-avian dinosaurs.

What we know

• The Cretaceous-Paleogene boundary is typically a thin band of rock marking the end of the Cretaceous Period and the beginning of the Paleogene Period. [1, 2]
• Boundary clay across the globe shows unusually high concentrations of the metal iridium, which is much more common in asteroids than in the Earth's crust. [3, 4, 5]
• The unusually high level of iridium was reported in 1980 by Luis and Walter Alvarez, who argued that an asteroid impact accounted for its presence. [5]
• The scientific consensus accepts that the impact matching the boundary and its ejecta layer triggered the Cretaceous-Paleogene mass extinction. [2, 5]

Still open

• While climate-modeling favors the asteroid impact, other proposed or contributing factors to the mass extinction have included Deccan Traps volcanism, climate change, and sea level change.

Where to go next

• what caused itWhat caused the Cretaceous-Paleogene mass extinction?
• what followedHow did mammals diversify after the extinction event?
• how it workedHow does an impact winter halt photosynthesis?
• how we knowWhat evidence links the Chicxulub crater to the extinction?
• whoWho were Luis and Walter Alvarez?
• an unexpected connectionHow is chalk etymologically linked to the K-Pg boundary?The word Cretaceous derives from the Latin for chalk, which is abbreviated as K in German as Kreide, providing the literal K in the K-Pg boundary name.

Sources

• [1]Cretaceous–Paleogene boundary (Wikidata Q682871) · CC0 1.0
• [2]Cretaceous–Paleogene boundary · CC BY-SA 4.0
• [3]Iridium anomaly · CC BY-SA 4.0
• [4]Cretaceous–Paleogene extinction event · CC BY-SA 4.0
• [5]Timeline of Cretaceous–Paleogene extinction event research · CC BY-SA 4.0