At the end of the Proterozoic, the supercontinent [[Pannotia]] had broken apart in the smaller continents [[Laurentia]], [[Baltica]], [[Siberia (continent)|Siberia]] and [[Gondwana]]. During periods when continents move apart, more [[oceanic crust]] is formed by volcanic activity. Because young volcanic crust is relatively hot and less dense than old oceanic crust, the ocean floors will rise during such periods. This causes the [[sea level]] to rise. Therefore, in the first half of the Paleozoic, large areas of the continents were below sea level.

Early Paleozoic climates were generally warmer than today, but the end of the Ordovician saw a short [[ice age]], in which glaciers covered the south pole, where the huge continent Gondwana was situated. Traces of glaciation from this period are only found on former Gondwana. During the Late Ordovician ice age, a number of mass extinctions took place, in which many [[brachiopod]]s, trilobites, [[Bryozoa]] and [[coral]]s disappeared. These marine species could probably not cope with the decreasing temperature of the sea water. After the extinctions new species evolved, more diverse and better adapted. They would fill the niches left by the extinct species.

The continents Laurentia and Baltica [[continental collision|collided]] between 450 and 400 million years ago, during the [[Caledonian Orogeny]], to form [[Laurussia]]. Traces of the mountain belt which resulted from this collision can be found in [[Scandinavia]], [[Scotland]] and the northern [[Appalachian]]s. In the [[Devonian]] period (416-359 million years ago) Gondwana and Siberia began to move towards Laurussia. The collision of Siberia with Laurussia caused the [[Uralian orogeny|Uralian Orogeny]], the collision of Gondwana with Laurussia is called the [[Variscan Orogeny|Variscan or Hercynian Orogeny]] in Europe or the [[Alleghenian Orogeny]] in North America. The latter phase took place during the [[Carboniferous]] period (359-299 million years ago) and resulted in the formation of the last supercontinent, Pangaea.

हिमाच्छादित पृथ्वी आणि ओझोन आवरणाची उत्पत्ती
सजीवसृष्टीची सुरुवात
पृथ्वीचा गाभा आणि पहिले वातावरण
Paleozoic tectonics, paleogeography and climate