Manson impact structure
impact crater
The Manson impact structure is an impact structure near the city of Manson, Iowa where an asteroid or comet nucleus struck the Earth during the Cretaceous Period, approximately 74 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 dinosaurs until isotopic ages proved that it was too old.
Description
No surface evidence exists due to comparatively recent coverage by glacial till, and the site where the impact structure lies buried is now a flat landscape. But, hidden about 20 to 90 m (66 to 295 ft) below the surface is a buried structure about 38 km (24 mi) in diameter. It lies under the southeast corner of Pocahontas County and extends under portions of three adjoining counties. That an anomalous structure underlaid the area was known from unusual water well drill cuttings in 1912 of deformed rock, "crystalline clast breccia with a melt matrix" as a later report described it. A research investigation was started in 1955, and it was labeled a "cryptovolcanic structure" (a hypothetical volcanic steam explosion). Further investigation was undertaken by Robert S. Dietz who proposed an impact origin in 1959 and by Nicholas Short in 1966 who produced evidence of shocked quartz grains which confirmed the impact origin of the structure.
In 1991 and 1992 the U.S. Geological Survey along with others including the Iowa Geological Survey conducted detailed research in part to test the possible connection of the Manson impact structure with the Cretaceous–Paleogene extinction event.
The public source identifies “Manson impact structure” as impact crater. This brief keeps that definition visible, then builds a research path around Manson, impact and structure.
Why this record matters
A short description can identify a subject without explaining its stakes. For “Manson impact structure”, the useful work is to connect “impact crater” to the records capable of establishing context and consequence.
Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jul 22, 2026. The linked authority identifier is Q3503047. Authority coordinates are 42.583, -94.550. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank. The first chronological checks are 1912, 1955, 1959 and 1966.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Manson impact structure”, its source revision and the description used here.
- Expand the search: follow Manson impact structure primary sources, Manson impact structure archive and Manson research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Manson impact structure”?
- Which institution is responsible for the underlying evidence?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “Manson impact structure” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.