Ordovician period dating
Image: An Ordovician drama - an endocerid cephalopod captures a trilobite. During the Ordovician, Southern Europe, Africa, South America, Antarctica and Australia remained joined together into the supercontinent of Gondwanaland, which had moved down to the South Pole.
North America straddled the equator, and was about 45 degrees clockwise from its present orientation.
Tectonic evidence suggests that the single supercontinent Rodinia broke apart and by the early to mid-Cambrian there were two continents.
Gondwana, near the South Pole, was a supercontinent that later formed much of the land area of modern Africa, Australia, South America, Antarctica and parts of Asia.
1), which represents an update containing the unit names and boundary age estimates ratified by the International Commission on Stratigraphy (ICS). North American Commission on Stratigraphic Nomenclature, 2005, North American stratigraphic code: American Association of Petroleum Geologists Bulletin, v.
Scientists should note that other published time scales may be used, provided that these are specified and referenced (for example, Palmer, 1983; Harland and others, 1990; Haq and Eysinga, 1998; Gradstein and others, 2004; Ogg and others, 2008).
Fossils of soft-bodied animals are a rare find because squishy body parts tend not to hold up as well as hard shells and bones over time, wearing away before they can leave an impression.
On the coattails of the famous Cambrian Explosion (around 530 million years ago) — which saw the establishment of all the major animal groups and the development of complex ecosystems — was the Great Ordovician Biodiversification Event (around 490 million years ago).
For consistent usage of time terms, the USGS Geologic Names Committee (GNC; see box for members) and the Association of American State Geologists (AASG) developed Divisions of Geologic Time (fig. (Also available at Ogg, Gabi, comp., 2009, Global boundary stratotype sections and points (GSSP): International Commission on Stratigraphy, accessed May 10, 2010, at Advances in stratigraphy and geochronology require that any time scale be periodically updated. Geological Survey (USGS), State geological surveys, academia, and other organizations have sought to create a consistent time scale to be used in communicating ages of geologic units in the United States. Therefore, Divisions of Geologic Time, which shows the major chronostratigraphic (position) and geochronologic (time) units, is intended to be a dynamic resource that will be modified to include accepted changes of unit names and boundary age estimates. Many international debates have occurred over names and boundaries of units, and various time scales have been used by the geoscience community. R., comp., 1983, The Decade of North American Geology [DNAG] 1983 geologic time scale: Geology, v. Paleontologists found more than 1,500 soft-bodied marine animal fossils, some dating to nearly 500 million years ago.
The discovery provides a more complete understanding of marine life at that time and suggests that these soft-bodied sea animals did not die off during a major extinction event during the Cambrian period, as previously thought.The end of the period is marked by an extinction event.