Editing Grove Karl Gilbert (section)

===Meteor crater===
In 1891, Gilbert examined the origins of a crater in Arizona, now known as [[Meteor Crater]] but then as Coon Butte. For several reasons, and against his intuition, he concluded it was the result of a [[Maar|volcanic steam explosion]] rather than an impact of a [[meteorite]]. Gilbert based his conclusion on the beliefs that the volume of an impact crater including the meteorite should be more than the ejected material on the rim and that, if it was a meteorite, iron should create magnetic anomalies. Gilbert's calculations showed that the crater's volume and the debris on the rim were roughly equal, and that there were no magnetic anomalies. He argued that the meteorite fragments found on the rim were just "coincidence". In 1892, Gilbert delivered his paper "The Moon's Face; A Study of the Origin of Its Features" as his retiring President's lecture to the Philosophical Society of Washington, and it was published in the Society's bulletin.<ref name = "Gilbert">{{cite journal |last1=Gilbert |first1=G. K. |title=The Moon's face; a study of the origin of its features |journal=Bulletin of the Philosophical Society of Washington |date=1892 |volume=12 |pages=241–292 |url=https://www.biodiversitylibrary.org/item/252085#page/311/mode/1up}}</ref> He publicized these conclusions in a series of lectures in 1895.<ref>{{Cite web |url=http://www.barringercrater.com/science/ |title=The Science: What is the Barringer Meteorite Crater? |access-date=2008-09-16 |archive-url=https://web.archive.org/web/20080719102623/http://www.barringercrater.com/science/ |archive-date=2008-07-19 |url-status=dead }}</ref> Later investigations revealed that it was in fact a meteor crater, but that interpretation was not well established until the mid-20th century. As part of his interest in crater origins, Gilbert also studied the moon's craters and concluded they were caused by impact events rather than volcanoes, although he wondered why the craters were round and not oval as expected for an oblique impact. The interpretation of lunar craters as of impact origin was also debated until the mid-20th century.<ref name=DRO-GS2002>{{cite book|last=Oldroyd|first=David Roger|title=The earth inside and out: some major contributions to geology|year=2002|publisher=Geological Society|pages=28–30}}</ref>