In the universe our great Doctor inhabits there are four distinct timelines he has lived through.
In this lesson, we shall learn the histories of these timelines, and more importantly, our history throughout them.
The first timeline was the original.
This is the timeline the Doctors one through three inhabited. The Time lords were a stuffy bureaucratic race and the Daleks were a race of exterminating psychopaths that created one of the greatest empires in history - and the most terrifying.
Humanity was a force to be reckoned with. Similar to the current timeline up to the 1980's it was a race of the most confused beings in the universe. By our time it would be similar, if it wasn't for the interference of the Doctor. In the 1980's, he inadvertently advanced human science by years, with fully functioning Z-Bombs being developed by 1986 (seventy years early).
By the mid-twenty first century, humanity had achieved faster-than-light travel establishing an empire that rivalled the Daleks. Its government, over its million year existence, would consistently alternate between libertarian, fascist and near anarchic governments.
By the twenty-second century, Earth was merely another planet in the empire. When it was invaded by the Daleks in 2164, it was barely a footnote. It was abandoned afterwards ten thousand years.
Near the end of its life, nostalgia and curiosity led to its rediscovery, with the now aging empire, and its crowning as humanity's homeworld.
However, the dying sun led the human race to abandon the Earth in mighty arks, leaving the planet to finally die in the year 10 million due to the sun going supernova (this was caused by exhaustive solar mining - had humans not evolved, the sun could have lasted to up to 5 billion years).
When the Doctor went back in time to stop the development of the Daleks, he permanently altered the timeline.
The Daleks instead of having hit and miss attempts at evolution during the development days as a space-faring race, they developed entirely during the thousand years they were trapped in the Kaled undercities. They abandoned Skaro and almost immediately entered the war with the Movellans. They were thoroughly trounced and reduced to a joke to the entire universe.
Davros, their creator, reappeared after thousands of years and took control. The Daleks didn't appreciate his leadership and overthrew him, building a new empire. Davros, through planets such as Necros and Planet 2 developed a new breed of Daleks and the Daleks were plunged into civil war. The war ended when the Doctor destroyed Skaro.
Without the Daleks to interfere and invade London, Earth became a major political power once again with the Human government becoming a consistent republican humanitarian force in the universe, with it being known for its uniqueness in Galaxy One.
However, the Daleks rebuilt Skaro and declared war with the Time Lords. While it began as a simple war, it soon blew up into a time war, the Last Great Time War. This timeline burnt and was reduced to almost nothing by the war. Everything died and everything lived. Creation ended and began and ended again. Everything happened at once.
This ended when the Doctor ended it. Ending this timeline once and for all.
Time was ravaged. War had burnt it.
Several species from before never existed. Some were exterminated to the point of extinction. Others were held back at several points in their timeline.
The Daleks and the Time Lords were removed from existence, leaving nothing but stories of things that never happened.
Humanity was held back. They never developed all things they did in the twentieth century, with Z-Power and Faster-than-light travel only beginning in the twenty-second century. In space, they were a xenophobic race with a tendency with starting wars with every species they come across for another 100,000 years.
They became extreme isolationist for another million years, with true diplomatic relations only being formed a long time afterward.
The Earth was destroyed in the year 5 billion, with all of humanity watching, truly at peace with the universe. They colonized a new planet, christened it New Earth and continued existing to the universes end.
The Doctor rebooted the universe and subconsciously moulded it to suit his liking. He made it more exciting.
The Daleks had returned as an isolationist power around Skaro, a ruined and war-torn planet.
The Earth Empire developed in the late twenty-first century, with it becoming a peaceful force in the galaxy. Earth was abandoned within two million years of this, due to solar flares. It was never returned to, unfortunately.
The Earth Empire was ruled by the papal mainframe, the church who provided the army and the government. They tracked time travellers with the help of their time agency, who especially monitored the Doctor.
They did this because of one thing. On every planet, there is a message carved into history. It confuses some. It terrifies others. And it drives some to kill the Doctor.
That message is Doctor Who?
And it must never be answered, lest the universe burn again.