Early major events, a mixture of myth and history:
Age of Creation: Golarion's creation is indefinite, with different groups telling different stories. For unknown ages, aboleths ruled the oceans and Vault Dwellers kept the land. Mortals eventually arose from somewhere, but from where is also debated. It was during this time Rovagug, The Rough Beast, god of destruction, disaster, and wrath, was trapped deep in the core of the world by an alliance of all the other gods. Sarenrae, The Dawnflower, goddess of healing, honesty, redemption, and the sun, cleft a rift into the world and thrust Rovagug into a strange dimension therein. Asmodeus, Prince of Darkness, god of contracts, pride, slavery, and tyranny, provided a lock and a key to Rovagug's prison.
Age of Serpents: One of the first mortal empires was founded by the serpentfolk, long since defeated by Azlant, the first human civilization.
Age of Legend: Technological and magical discoveries were made by the Azlanti the likes of which are now unknown. A second empire, Thassilon, was founded by a group of separatists in the northwest part of the continent of Avistan. The rulers of both of these empires grew to be proud and haughty, so their aboleth enemies decided to end things on their own terms, with an event now called Earthfall.
Age of Darkness:
-5293 to -4295: Earthfall. The Starstone crashes down across the land bridge connecting Avistan and Garund, carving out the Inner Sea and causing darkness to cover the world (mostly Avistan, Garund, and Casmaron) for a millennium. Azlant and Thassilon are destroyed, and humans are forced to do they can to survive. Elves, who had been present but less dominant than the humans, flee through magical gates, cross the Crown of the World, or hide in the Darklands. Dwarves, living in other areas of the Darklands, undertake their great Quest for the Sky, driving their ancient Orc enemies before them as they push upwards.
Age of Anguish:
-4294 to -3471: The darkness passes and humans begin rebuilding civilization. The gnomes arrive on Golarion, fleeing an unknown terror of the First World. The pit of Gormuz opens in Casmaron, disgorging the first Spawn of Rovagug. Old-Mage Jatembe, a powerful mage in the Mwangi expanse of Garund, brings the light of learning back to the world.
Age of Destiny:
-3470 to -1: Osirion is founded, ruled by God-Kings and Pharaohs, then falling into decline. Taldor is founded by descendants of Lost Azlant.
Age of Enthronement:
1 to 4605: Aroden, last of the Azlanti, raises the Starstone from the sea, founds the city-state of Absalom, and becomes god of human culture, innovation, and history. The Taldan empire expands due to the efforts of several Armies of Expansion. Aroden leads Taldor against the wizard-king Tar-Baphon, who later rises as the most powerful lich ever known, The Whispering Tyrant. Norgorber, Cayden Cailean, and Iomedae all pass the test of the starstone during this time, ascending to godhood. Cheliax is founded in western of Taldor, eventually secedes, and gradually supplants the Taldan empire as the preeminent human society. Chelish forces found Korvosa in southeast Varisia and push the native Shoanti tribes out of the fertile southern lands onto the arid Storval Plateau. A group of settlers leave Korvosa and found Magnimar in western Varisia. Baba Yaga conquers the eastern territories of the Land of the Linnorm Kings, founding the country of Irrisen. Cheliax prepares for the Prophesied return of Aroden to lead the empire in the coming Age of Glory.
Age of Lost Omens:
4606 to now: Rather than Aroden appearing, three storms wracked Golarion, one remaining as the eye of Abendago. Aroden's clerics found themselves disconnected from their god, who is now assumed dead. Cheliax falls into civil war, resulting in the Asmodeus-worshipping House Thrune taking the throne. Thousands of disaffected citizens leave Korvosa for Magnimar.