• 86% of species lost
      • diversity of life increases, fish are the first true vertebrates;
      • O2 68 % of modern level;
      • mean surface temperature 2 °C above modern level;
      • sea level 180m above present day, rising to 220 m and falling sharply to 140 m in end-Ordovician glaciation;
      • 100 times as many meteorites struck the Earth per year during the Ordovician compared with today;
      • Appalachians first formed, Laurentia and Gondwana hover near equator, wide shallow seas; climate warm but later cools;
      • First life on land – primitive liverwort plants and fungi;
      • The period ends in ice age and extinction.


Name Diameter (km) Age (megayears) Dating method Morphological type Notes
James River, Alberta 4.8 <480 Geological dating PROBABLE Complex No surface expression
Clearwater East, Quebec 26 ~460–470 Rb-Sr melt rocks CONFIRMED Complex Chondrite-type
Calvin, Michigan 7.24 450 ± 10 Geological dating CONFIRMED Complex
Pilot Lake, North West Territories 6 445 ± 2 K-Ar, 40Ar/39Ar and Rb-Sr CONFIRMED Complex Dating based on one sample
Bear Swamp, New York 3.5 ~444 Geological dating PROBABLE Simple No surface expression
Glasford, Illinois ~4 443.8-485.4 Geological dating CONFIRMED Complex Shattercones, shock metamorphism


86% of species lost — 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 newly exposed silicate rock sucked CO2 out of the atmosphere, chilling the planet.

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.

Paleogeography of Baltica and neighboring cratons at the time of the increased cosmic bombardment following the ~470 Ma asteroid breakup event illustrating the resulting known craters (red dots). Clearwater East is dated to this event (~460–470 Ma). Light blue color represents areas of shallow epicontinental seas, and dark blue areas of deep ocean. This distribution may, however, have varied somewhat due to periodical transgressions and regressions of the sea. The timeline documents the related meteorite falls (black dot and line).

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. At that time CO2 was at 17 times that of present levels and the first terrestrial moss-type (bryophyte) fossils appear.

North American Middle Ordovician impact craters. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Impact Structure, Wisconsin, 4: Slate Islands, Ontario.The Ordovician–Silurian extinction event, the Ordovician extinction, 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.

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]


1. 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.

2. 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).

3. 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.

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