Ordovician meteor event

File:Middle Ordovician craters.jpg

North American Middle Ordovician impact craters. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Disturbance, 4: Slate Islands crater.

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If the line of North American Middle Ordovician impacts is extended on the modern globe it leads to the impact area of southern Sweden. Although this is suggestive of a single large meteorite shower, the exact alignment of continental plates 470 million years ago is unknown and the exact timing of meteors is also unknown.

Approximately 9 m (30 ft) tall shatter cone in McGreevy Harbour, Slate Islands in Lake Superior.

The Ordovician meteor event is a proposed shower of L chondrite meteors that occurred during the Middle Ordovician period, roughly 470 million years ago. This theory was proposed by Swiss and Swedish researchers based on the comparatively tight age clustering of L chondrite grains in sediments in southern Sweden and at the Neugrund crater in Estonia. They proposed that a large asteroid transferred directly into a resonant orbit with Jupiter, which shifted its orbit to intercept Earth. In addition to the northern European evidence, there is circumstantial evidence that several Middle Ordovician meteors fell roughly simultaneously 469 million years ago in a line across North America, including the Ames crater in Oklahoma, the Decorah crater in Iowa, the Slate Islands crater in Lake Superior, and the Rock Elm crater in Wisconsin. It is hypothesized that this shower was associated with, or possibly caused, the Great Ordovician Biodiversification Event.