The Early Paleozoic Era includes the Cambrian and Ordovician periods from ~542 444 million years ago. At the beginning of the Cambrian, the continents were breaking up from a Precambrian supercontinent (Rodinia then Pannotia). The two major landmasses that resulted from this supercontinent split were Gondwana and Laurentia. Laurentia underwent major flooding due to sea level rise in the Cambrian period, which deposited marine sediment far inland of the continental margin and can be found in the rock record of the North American continent today. The deposits from this sea level rise and flooding is called the Sauk transgression which overlies the Great Unconformity.
The Cambrian was also a period with numerous mass extinctions. Some of the Cambrian extinctions are associated with climate change, but some Cambrian extinctions remain unexplained, and may be due to evolutionary experimentation.
The Ordovician brought glaciation in the southern hemisphere on Gondwana which lowered the sea level after the Sauk transgression and caused major climate change leading to the first of the Big 5 mass extinctions of the Phanerozoic Eon.
The Ordovician also marked tectonic events that built mountains, namely, the first orogeny in a series of mountain building collisions that built the Appalachians, the Taconic Orogeny.
The Burgess Shale formed at the base of the passive margin of Laurentia during the Early Paleozoic and perfectly preserved many softbodied Cambrian organims that would not have been preserved if it wasn't for this pristine, anoxic presevation environment.
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0:00 Timeline & Geology Summary
1:20 Cambrian paleogeography
2:10 Cambrian flooding
5:00 Deposition from flooding
6:22 Cambrian extinctions
9:25 Ordovician paleogeography
10:17 Ordovician glaciation
12:04 Ordovician mountain building
16:13 Burgess Shale environment
18:16 Related videos & references
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