Editing Decorah, Iowa (section)

===Impact crater===
{{main|Decorah crater}}
About 470 million years ago, a meteorite as big as a city block smashed into what is now Decorah, supporting a theory that a giant space rock broke up and bombarded Earth just as early life began flourishing in the oceans.<ref name="Crater found">{{cite news|first=Brian|last=Vastag|title=Crater found in Iowa points to asteroid break-up 470 million years ago |url=https://www.washingtonpost.com/national/health-science/crater-found-in-iowa-points-to-asteroid-break-up-470-million-years-ago/2013/02/18/545131f8-76d5-11e2-aa12-e6cf1d31106b_story.html|newspaper=The Washington Post|date=2013-02-18}}</ref>

The impact dug a crater nearly four miles wide that now lies beneath the town, said Bevan French, one of the world's foremost crater hunters and an adjunct scientist at the National Museum of Natural History.<ref name="Crater found"/>

The Decorah crater lay undiscovered until recently because almost none of it is above ground. Instead, it is filled by an unusual shale that formed after an ancient seaway sluiced into the crater, depositing sediment and an array of bizarre sea creatures that hardened into fossils.<ref name="Crater found"/> One such creature is ''[[Pentecopterus decorahensis]]'', which was named for the city.<ref name="BMC-20150901">{{cite journal |last1=Lamsdell |first1=James C. |last2=Briggs |first2=Derek E. G. |last3=Liu |first3=Huaibao |last4=Witzke |first4=Brian J. |last5=McKay |first5=Robert M. |title=The oldest described eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek Lagerstätte of Iowa |date=1 September 2015 |journal=[[BMC Evolutionary Biology]] |volume=15 |pages=169 |doi=10.1186/s12862-015-0443-9 |pmid=26324341 |pmc=4556007 |doi-access=free }}</ref>