The Ordovician Period is the second period of the Paleozoic Era and began 485.4 million years ago and ended 443.4 million years ago (when the Silurian Period began). Four continents were present and separated by three main oceans. Laurentia was composed of present-day North America, part of Scotland, and Greenland and was near the equator. Siberia-Kazakhstan was east of Laurentia, slightly north of the equator. The Iapetus Ocean separated these two masses on the south from the continent of Baltica. Avalonia (England, New England, and parts of Canada) was to the west of Baltica. England, Baltica, and Kazakhstan were separated from Gondwana by the Paleotethys Sea. At this time, Africa and South America were rotated almost 180° from their current location. The Panthalassic Ocean covered the Northern Hemisphere almost completely.
The rate of seafloor spreading was minimal during the Ordovician Period but thanks to high oceanic ridges, the seafloor became elevated and many parts of the continents were flooded. Shallow seas within the continents were thus formed. Sea levels fluctuated constantly maybe due to the rates of plate motion, ice caps, etc. The major tectonic plates were moving during this period so volcanism was extensive, peaking twice during the early Paleozoic Era. Mountain building belts were created wherever plates converged as well.
The levels of carbon dioxide in the atmosphere were 15 times higher than they are today and this was due to the volcanic activity, which released enormous amount of carbon dioxide gas into the atmosphere. The flooding of continents and the lack of plants on land also contributed to the heightened levels. These conditions created a greenhouse effect so tempera...
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...nd Stromatoporoids (a kind of sponge with a layered skeleton) were common rock builders of the Northern Hemisphere. Moss was common in shallow seas. Among the arthropods, the giant eurypterids (sea scorpions) have been found in the Old Red Sandston facies (see image above). The first insect was part of a group of wingless insects that feed off of debris and soil. Conodonts were vertebrate animals abundant in marine life. Many of the fish were heavily armored and the earlier fish (agnathans) had no jaws and were mud eaters and scavengers. Chondrichthians are sharklike fishes that were first found in the Middle Devonian. In terms of plants, many vascular plants emerged and a varied flora was established. There is evidence of algae, bryophytes, and charophytes. Algae and fungi also existed. As previously stated, the first known forests are from the Devonian Period.
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