86% of species lost

The Ordovician–Silurian extinction event, was the second-largest of the five major extinction events in Earth’s history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. This was the second biggest extinction of marine life, ranking only below the Permian extinction. At the time, all known life was confined to the seas and oceans. More than 60% of marine invertebrates died including two-thirds of all brachiopod (hard upper/lower shells) and bryozoan (aquatic invertebrates) families.

— Graptolite 2-3 cm length

Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding animals and colony builders. Their demise over about a million years was probably caused by a short, severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians. The first terrestrial moss-type (bryophyte) fossils appear.

The Late Ordovician (Sandbian) Glasford structure: A marine‐target impact crater with a possible connection to the Ordovician meteorite event Meteoritics & Planetary Science 1–24 (2019)

The Glasford structure in Illinois (USA) was recognized as a buried impact crater in the early 1960s but has never been reassessed in light of recent advances in planetary science. Here, we document shatter cones and previously unknown quartz microdeformation features that support an impact origin for the Glasford structure. We identify the 4 km wide structure as a complex buried impact crater and describe syn‐ and postimpact deposits from its annular trough. We have informally designated these deposits as the Kingston Mines unit (KM). The fossils and sedimentology of the KM indicate a marine depositional setting. The various intervals within the KM constitute a succession of breccia, carbonate, sandstone, and shale similar to marine sedimentary successions preserved in other craters. Graptolite specimens retrieved from the KM place the time of deposition at approximately 455 ± 2 Ma (Late Ordovician, Sandbian). This age determination suggests a possible link between the Glasford impact and the Ordovician meteorite shower, an increase in the rate of terrestrial meteorite impacts attributed to the breakup of the L‐chondrite parent body in the main asteroid belt. (MONSON 2019)

First known Terrestrial Impact of a Binary Asteroid from a Main Belt Breakup Event

Jens Ormö, Erik Sturkell, Carl Alwmark & Jay Melosh

ABSTRACT: Approximately 470 million years ago one of the largest cosmic catastrophes occurred in our solar system since the accretion of the planets. A 200-km large asteroid was disrupted by a collision in the Main Asteroid Belt, which spawned fragments into Earth crossing orbits. This had tremendous consequences for the meteorite production and cratering rate during several millions of years following the event. The 7.5-km wide Lockne crater, central Sweden, is known to be a member of this family. We here provide evidence that Lockne and its nearby companion, the 0.7-km diameter, contemporaneous, Målingen crater, formed by the impact of a binary, presumably ‘rubble pile’ asteroid. This newly discovered crater doublet provides a unique reference for impacts by combined, and poorly consolidated projectiles, as well as for the development of binary asteroids.

The Österplana 065 fossil meteorite from the Glaskarten 3 bed. The meteorite is 86.52 cm large. It is surrounded by a grey reduction halo, in the otherwise red limestone. Oxygen was consumed when the meteorite weathered on the sea floor. The coin in the image has a diameter of 2.5 cm.. Credit: Image courtesy of Lund University.

The red dot represents the approximate area of the possible multiple impact in the late Ordovician Period.

The red dot represents the approximate area of the Pilot Lake impact 445 million years ago in the Ordovician Period.
North American Middle Ordovician impact craters. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Impact Structure, Wisconsin, 4: Slate Islands, Ontario.

Evidence for Impact: 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.[1][2][3] 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 Decorah crater in Iowa, the Slate Islands crater in Lake Superior, and the Rock Elm crater in Wisconsin.[4]

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Rock Elm, Wisconsin 6 ~450 Geological dating CONFIRMED Complex Youngest exposed rocks



Heck, Philipp; Birger Schmitz, Heinrich Baur, Alex N. Halliday. Rainer Wieler (15). “Fast delivery of meteorites to Earth after a major asteroid collision”. Nature 430: 323-325.

H. Haack et al. Meteorite, asteroidal, and theoretical constraints on the 500-Ma disruption of the L chondrite parent body, Icarus, Vol. 119, p. 182 (1996).

Korochantseva et al. “L-chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar-39Ar dating” Meteoritics & Planetary Science 42, 1, pp. 3-150, Jan. 2007.

Charles C. MONSON, Dustin SWEET, Branimir SEGVIC, Giovanni ZANONI,
Kyle BALLING, Jacalyn M. WITTMER, G. Robert GANIS, and Guo CHENGThe Late Ordovician (Sandbian) Glasford structure: A marine‐target impact crater with a possible connection to the Ordovician meteorite event Meteoritics & Planetary Science 1–24 (2019)

Vastag, Brian (18 February 2013). “Crater found in Iowa points to asteroid break-up 470 million years ago”. Washington Post. Retrieved 19 February 2013.