What occurred during the Perian period that drastically altered organism population on Earth? Be detailed

The Permian period, which ended in the largest mass extinction the Earth has ever known, began about 299 million years ago. The emerging supercontinent of Pangaea presented severe extremes of climate and environment due to its vast size. The south was cold and arid, with much of the region frozen under ice caps. Northern areas suffered increasingly from intense heat and great seasonal fluctuations between wet and dry conditions. The lush swamp forests of the Carboniferous were gradually replaced by conifers, seed ferns, and other drought-resistant plants.

Early reptiles were well placed to capitalize on the new environment. Shielded by their thicker, moisture-retaining skins, they moved in where amphibians had previously held sway. Over time, they became ideally suited to the desert-type habitats in which they thrive today.
Hope it is helpful

1) ^^ population, individuals

2) speciation

3) A,C