Short answers, pulled from the story.
Adam Sedgwick first used the name Paleozoic in 1835 to describe rock layers containing Cambrian and Ordovician fossils. John Phillips redefined the term two years later in 1840 to include all periods from the Cambrian through the Permian.
Geologists now date the start of this era at 538.8 million years ago. This specific number marks the boundary between the Neoproterozoic Eon and the Phanerozoic Eon.
International Commission on Stratigraphy members eventually chose a site called Fortune Head on the Burin Peninsula in Newfoundland as the Global Stratotype Section and Point. This location sits below the first appearance of both trilobites and small shelly fauna.
The breakup of the supercontinent Pannotia began with the opening of the Iapetus Ocean during the early Cambrian period. Continental collisions later formed the supercontinent Pangaea by the late Paleozoic.
The final catastrophe occurred at the start of the Mesozoic Era 251.9 million years ago. Ninety-five percent of all life on Earth disappeared during the Permian-Triassic extinction event known as The Great Dying.