The end-Paleozoic extinction, the largest in magnitude, determined the fate of modern animals including human beings. It occurred in two steps: first around the end-Middle Permian (Guadalupian-Lopingian boundary; G-LB) and then at the end-late Permian (Permian-Triassic boundary; P-TB). Biological and non-biological aspects unique to the first event include significant drop in biodiversity, changes in isotope ratios (C, Sr etc.) and redox state of seawater, sea-level drop, episodic volcanism, and change in geomagnetic reversal pattern. These global phenomena suggest that the ultimate cause was not on the planet’s surface but was related to changes within the planet’s interior. Among the major extinctions in the Phanerozoic, the G-LB and end-Ordovician events share multiple similar geologic phenomena including the appearance of global cooling, suggesting that the same cause and processes occurred repeatedly at least for the two events. The extinction-scenario with mantle plume-generated large igneous provinces (LIPs) seems difficult to explain the repeated cooling-associated extinctions during the Phanerozoic. The similarity between the end-Ordovician and G-LB particularly indicates that drop in atmos. CO₂ alone could not equally trigger the cooling and relevant extinction both in pre- and post-green (terrestrialization) world. Instead, star-burst events (massive formation of stars) detected in the Milky Way Galaxy apparently coincide in timing with the cooling-associated major extinctions of the Phanerozoic, e.g. end-Ordovician, Late Devonian, and G-LB episodes, and also with the Proterozoic snowball Earth episodes at ca. 2.3 Ga and 0.7 Ga. Episodic passage of dark clouds (blocking irradiance), and/or increased flux of galactic cosmic radiation (GCR) (cloud coverage), likely caused the major events of global cooling and associated extinction in the past. Material-based evidence for the extraterrestrial forcing immediately before the cooling-associated extinctions is lately appearing. The study of mass extinctions on Earth is entering a new stage with a new cosmoclimatological perspective.