Earth's (known only as Terra in the 41^st Millennium) early history has largely been lost, leaving little but legends and myths. All Imperial citizens know that the human race originated on Holy Terra, but beyond that they know nothing, save of course that it is the home of the God-Emperor and the Golden Throne – and compared to that, how important are a few history lessons!?

The Imperial Calendar currently in use was created by the Emperor following Unity on Terra to replace the myriad systems then in use. It is not known in the 41^st Millennium what he based the calendar dates upon; most likely he just took whatever calendar was most prevalent on Earth at the time and extrapolated from there. At least one semi-heretical school of thought claims that 001.M1 is actually the year of the Emperor's birth, while another holds that the beginning of M1 marks the beginning of human civilization, and a third claims that 001.M1 marks the year of the first human venture into space. The Administratum, the Ecclesiarchy and the Inquisition are all quick to suppress any secular speculation into Terra's or the Emperor's hallowed past.

Fragments of older dating systems can still be found here and there, but the Administratum is quick to correct any such instances that come to their attention – they have worked diligently for 10.000 years to standardize everything and do not take any deviance from the Holy System lightly. For non-official correspondence beyond the scrutiny of the Adepta local calendars are alive and well, especially on worlds whose length of year and day differ greatly from Terran standards. Indeed, when it comes to the counting of days and hours local systems hold sway.

The First Age of Terra (M1-M15)

In the beginning of the First Age humanity was bound to the homeworld, taking its first tenuous steps into space at some point during this Age. What actually happened on Earth during this period we will never know. Whatever physical evidence once existed has been destroyed by the passage of years and the total urbanization of Holy Terra. The only sources that remain are copies of copies of copies of works created by scholars of the Great Crusade Era – some originals supposedly having been written by the Emperor himself, if such a thing be believed.

The Adeptus Mechanicus actually claims that Mars was visited by machine probes prior to M3, that humans had set foot on the planet no later than 100.M3, and that before the end of M3 Mars had been made at least semi-habitable. It does seem incredibly unlikely, but the Adeptus Mechanicus is insistent. As if that wasn't enough there are scholars of good repute that claim that man took to the stars long before the beginning of the Dark Age of Technology. Some even go as far as claiming that man held the secrets of warp-travel millennia before what is commonly accepted.

Dark Age of Technology (M16-26)

The Dark Age of Technology is characterized by humanity's unbridled expansion across the galaxy and the technological supremacy that allowed it to go where it wanted and to do as it pleased. It is sometimes referred to as the Golden Age of Humanity, but only by those blind to the godless ways that eventually paved the way for the Age of Strife. At the height of this period there existed an estimated 70 million human-inhabited worlds, average population 100 billion, total population of about 7 million trillion (7x10¹⁸⁾.

Some Imperial scholars active at the end of the 41^st Millennium place the Dark Age of Technology in M18-M23, beginning with humanity's unbridled colonization of the galaxy in M18 and ending with the War Against the Abominable Intelligences late in M23.

M16 First major colonization drive beyond local star area initiated using massive warp-capable ark-ships, advanced AI robotics, and STC technology. Psykers scientifically proven to exist.

M18 Warp drives are perfected, increasing the speed and range of starships, making ark-ships obsolete and allowing humanity to reach even the most remote corners of the galaxy. A few scholars mark this millennium as the true beginning of the Dark Age of Technology.

M21 Great Diaspora – countless planets have been terraformed since the beginning of the Dark Age of Technology and are ready for settlement, setting the stage for a period of intense colonization, ending several thousand years later.

M22 Navigator Gene, astropsychic beacons and astrotelepathic communication developed, bringing humanity closer together, leading to Golden Age of Mankind. Expansion gradually stagnates as energy if focused on providing existing colonies with near-limitless standard of living.

M23 War between Stone Men and Iron Men – a galaxy-spanning war nearly destroys humanity as its robotic servants rise in rebellion. Machines eventually defeated and strict control of AI implemented. Some scholars mark this as the beginning of the Age of Strife as it marks the end of the utopian golden years of humanity.

M24 Humans continue to rule the galaxy unchallenged, but much has been lost in the Machine Wars. Without access to an infinite supply of skilled machine labor the standard of living is nowhere near what it was, at least for the masses.

Late.M25 Increasing warp-turbulence makes travel and communication increasingly difficult, causing the collapse of pan-galactic human civilization and replacing it with regional or local political powers. Powerful psykers emerge in hitherto unprecedented numbers.

Age of Strife (M26-M30)

The Age of Strife put an end of man's unchallenged domination of the galaxy. Even during the Dark Age of Technology the Immaterium was ill understood, and scientists could offer no rational explanation (though many tried) as to why it had suddenly become tumultuous and chaotic in the extreme. It eventually became impossible to navigate or communicate between the stars, putting an end to galactic civilization. In addition many people were driven insane by warp pressure, and many of the emerging psykers become outright possessed by daemonic entities (and even if they did not succumb to possession they were terribly dangerous and often mentally deranged). Once again neither effect was well understood at the time, and science could neither explain nor counteract these new developments.

Across the galaxy human civilization broke down on countless worlds, resulting either in the total extinction of the human population or a reversal to a more primitive state. Only a small fraction of human worlds survived at all, a few per cent at most. Even where a world survived it would likely see great suffering, loss of life, and erosion of technological capabilities. At one point the total human population might have been as low as a few hundred trillion (extreme estimate) or perhaps in the low thousands (a more conservative estimate). Dead worlds dot the galaxy even today, awaiting discovery by rogue traders and explorator fleets.

M26 Interstellar travel and communication finally collapses completely down in face of ever-more violent and persistent warp disturbances. Manifesting daemons, rogue psykers and mass warp-madness cause widespread destruction and collapse of civilization.

M28 Earth government, which has endured so far, breaks down. The planet experiences a tumultuous period of two and a half thousand years of war and atrocity, eventually leading to the near destruction of civilization on the human homeworld.

M30 The Emperor reveals himself on Terra and starts preparations for Unity.