ORDOVICIAN PERIOD 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). There were four continents separated by three main oceans. Laurentia was made up of present-day North America, parts of Scotland and Greenland and was near the equator. Siberia-Kazakhstan was located east of Laurentia, slightly north of the equator. The Iapetus Ocean separated these two landmasses to the south from the Baltica continent. Avalonia (England, New England, and parts of Canada) was located west of Baltica. England, Baltica and Kazakhstan were separated from Gondwana by the Paleotethys Sea. At this time, Africa and South America had rotated nearly 180° from their current position. The Panthalassic Ocean almost completely covered the Northern Hemisphere. The rate of seafloor spreading was minimal during the Ordovician period, but thanks to high mid-ocean ridges, the seafloor rose and many parts of the continents were inundated. Shallow seas were thus formed within the continents. Sea level fluctuated constantly, perhaps due to the speed of movement of plates, ice sheets, etc. Major tectonic plates were moving during this period, so volcanism was extensive, peaking twice during the early Paleozoic era. Mountain belts also formed at the points where the plates converged. Carbon dioxide levels in the atmosphere were 15 times higher than today and this was due to volcanic activity, which released huge amounts of carbon dioxide gas into the atmosphere. The flooding of continents and the lack of plants on land have also contributed to the rising levels. These conditions created a greenhouse effect, so tempera...... middle of paper ...... and stromatoporoids (a kind of sponge with a layered skeleton) were common rock builders in the Northern Hemisphere. Moss was common in shallow seas. Among arthropods, 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 on debris and soil. Conodonts were vertebrate animals abundant in marine life. Many fish were heavily armored and the earliest fish (agnathan) had no jaws and were mud eaters and scavengers. Chondrichthyans are shark-like fish first found in the Middle Devonian. From a plant point of view, many vascular plants have emerged and a varied flora has formed. There is evidence of algae, bryophytes and charophytes. There were also algae and fungi. As stated previously, the earliest known forests date back to the Devonian period.