ORDOVICIAN PERIODThe Ordovician Period is the second period of the Paleozoic Era and began 485.4 million years ago and ended 443.4 million years ago years (at the beginning of the Silurian period). Four continents were present and separated by three main oceans. Laurentia was made up of present-day North America, part of Scotland and Greenland and was located near the equator. Siberia-Kazakhstan lay to the east of Laurentia, slightly north of the equator. The Iapetus Ocean separated these two masses to the south of the Baltica continent. Avalonia (England, New England and parts of Canada) was west of Baltica. England, the Baltic and Kazakhstan were separated from Gondwana by the Paleotethys Sea. At that time, Africa and South America were rotating almost 180° from their current locations. The Panthalassic Ocean covered almost the entire Northern Hemisphere. The rate of seafloor expansion was minimal during the Ordovician period, but thanks to high ocean ridges, the seafloor rose and many parts of the continents were flooded. Shallow seas within continents were thus formed. Sea level was constantly fluctuating, perhaps due to the speed of movement of plates, ice sheets, etc. The major tectonic plates were moving during this period, so volcanism was widespread, peaking twice in the early Paleozoic era. Mountain-forming belts were also created wherever 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 into the atmosphere. The flooding of continents and the lack of plants on land have also contributed to rising levels. These conditions created a greenhouse effect, so tempera... middle of paper ... and stromatopores (a kind of sponge with a layered skeleton) were common rock builders of the Northern Hemisphere. Moss was common in shallow seas. Among arthropods, giant eurypterids (sea scorpions) were 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 early fish (agnathans) had no jaws and were mud eaters and scavengers. Chondrichtians are shark-like fish that were first discovered in the Middle Devonian. At the plant level, numerous vascular plants have emerged and a varied flora has been established. There are traces of algae, bryophytes and charophytes. Algae and fungi also existed. As previously noted, the earliest known forests date from the Devonian period..