20 Dollars - Elizabeth II Chicxulub Crater

The Chicxulub crater, buried beneath the Yucatán Peninsula and the Gulf of Mexico, was definitively linked to the Cretaceous-Paleogene extinction event only in 1991, when Alan Hildebrand and colleagues published the identification — decades after the underlying iridium anomaly had been detected worldwide in the geological record. The impactor is estimated at roughly 10–15 kilometers in diameter, releasing energy orders of magnitude beyond any human-made weapon.

Cook Islands has issued science-themed collector silver under its numismatic licensing program since the early 2000s, with KM#2753 falling squarely in that category — a bullion-adjacent commemorative struck for the collector market, not circulation.