The Manson impact crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

is near the site of Manson, Iowa

Manson, Iowa

Manson is a city in Calhoun County, Iowa, United States. The population was 1,893 at the 2000 census.-Geography:Manson is located at . According to the United States Census Bureau, the city has a total area of , all of it land....

 where an asteroid or comet nucleus struck the Earth during the Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 Period, 74 Ma

Year

A year is the orbital period of the Earth moving around the Sun. For an observer on Earth, this corresponds to the period it takes the Sun to complete one course throughout the zodiac along the ecliptic....

 (million years ago). It was one of the largest known impact events to have happened in North America.Previously it was thought to have led to the extinction of the dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s until isotopic ages proved that it was too old.

No surface evidence exists due to comparatively recent coverage by glacial till

Till

thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....

, and the site where the crater lies buried is now a flat landscape.