Naturally, it's not going to give you anything other than the broad strokes of the meta-setting, and in fact some of the settings were fleshed out in separate (not-free) setting books from HERO Games.
Overall, it reminds me of three things: The History of the DC Universe which was published after the seminal Crisis on Infinite Earths maxi-series, the Planetary comics series by Warren Ellis and John Cassaday, and the Wold Newton Universe which grew out of Philip Jose Farmer's ingenious attempts to tie all manner of pulp heroes (and villains) into a single history and set of families.
The reasons it does this include: to create a massive backdrop against which Heroic and Super-heroic adventures may be played; to allow spaces in the timeline in which the various genres and sub-genres that super-heroic fiction might be played; to create rationale for bringing various NPCs and organizations backwards and forwards in the timeline.
Before I talk about the pros and cons of the approach, let me give you a taste of the various time periods (and descriptions + inspirations of each) tackled in the document. Much of it is taken from the PDF itself, though trimmed, edited and annotated by yours truly.
But let's start off with the era that seems most friendly to the type of settings found in OSR adventures -- the fantasy genre-friendly era:
The Pre-Cataclysm Period
The Pre-Cataclysm Period is an age of civilization prior to the recorded history of mankind. For flavor, think Robert E. Howard, Clark Ashton Smith, Jack Vance, Lord Dunsany, Michael Moorcock, Lin Carter, and the like.
Fantasy Primeval (100,000 TO 75,000 BC)
The first civilizations of men other sentient races -- such as Dwarves and Elves -- arise. Initially, many of the dreaded Elder Races control much of the planet, and dominate most of the races of men either directly or through fear, but are in decline, gradually leaving Earth after warring with each other for millennia.
The gods evolve, and many walk the Earth, using humans as pawns in their interminable wars with each other. At long last, the wars of the gods come to a head, and in a tremendous clash they break the world. Realizing they could destroy themselves by destroying their worshipers, the gods depart Earth for other dimensions, leaving the planet to settle down and the few surviving humans to rebuild their shattered civilizations.
Note: One might consider this very similar to the Runequest setting, where magics constantly shape the world, physics are just as valid in terms of world rules as arcana, and where battles of gods ensnare the lives of mortals.
Turakian Age (73,000 to 65,000 BC)
An age defined by the rise and fall of Kal-Turak, Ravager of Men, from whom this period takes its name. It ends with the overthrow of Kal-Turak at the hands of all the free peoples of the world, in a magical cataclysm that once again re-shapes the world.
Note: Kal-Turak acts much like a campaign's uber-baddie, kind of a Vecna meets Invincible Overlord meets Darkseid, and gets to return in various forms and guises in future ages of the timeline.
Valdorian Age (50,000 BC TO 33,000 BC)
The Valdorian Age -- named after a Hero Universe fantasy empire founded by its hero-king Valdor -- is a classic sword-and-sorcery style fantasy setting in the mode of Howard or Moorcock. Mankind remains the dominant race on the planet; other races go into decline (many apparently vanish). Fantastic creatures of all descriptions are found on the Earth (some remnants of the Primeval age, others newly arisen). The gods still exert a strong influence on the Earth through gateways, priests, and avatars.
Note: This age seems friendliest to a Conan-like campaign, or an Elric-like campaign, or a Fafhrd and the Grey Mouser campaign depending on where you adventure and how you arrange your nations and states.
Atlantean Age (32,000 TO ~30,000 BC)
Toward the end of the Valdorian Age, a new empire, the Dominion of Atlantis, arose. Based on an ancient island (of the same name) of great mystical power, Atlantis soon came to dominate most of the world. Around 30,500 BC, Dalsith, son of the rebellious warrior-king and sorcerer Cormar the Mighty, sacrificed his soul to the Kings of Edom for great mystical power and became Sharna-Gorak the Destroyer, Vondarien’s greatest enemy. The clash between Sharna-Gorak and the forces of Atlantis shook the earth, eventually sinking continents, toppling mountain ranges, and creating a great flood -- the Cataclysm.
Note: The Atlantean Age is a overpowered high fantasy campaign setting, where magic can push the power ratings to super-heroic levels. It has an eclectic cultural mix that is reminiscent of Barsoom or Jack Vance’s Dying Earth or perhaps even the Final Fantasy series of video games.
This takes place around ~30,000 B.C. and it changes the world yet again. It destroyed almost all traces of civilization prior to this time. The survivors were thrown back to Stone Age technology and magic.
Note: the function of the Cataclysm is meant to handwave all this hoo-hah about no evidence existing concerning pretty much everything that happened prior. There will be stories and accounts that might survive to the present day, but since terrible physical and magical energies laid waste to everything, what puny evidence might be found is inconclusive and certainly insufficient to draw any inference about the majestic histories that were wiped from memory.