Humanity is a scattered race. After they were 'uplifted' at the end of the 21st century by the Xarn, they were forced into a war with the Scree. Earth's defences were destroyed in 2109, and the Scree started colonisation and terraforming of Earth.
Pacification process of humans on Earth went drastically wrong (a disease used to cut down Earth's population to ~2billion left only 500 million). Earth is under the control of the Scree, who have done much work changing Africa to their tastes (the deserts are covered in lush alien plant life, and the native rain forests are fighting for survival against the new breeds of Scree plants).
The atmosphere has increased its oxygen content by 3% - not that many humans have really noticed.
Since the change in regimes in the Scree Empire, humans are starting to be allowed to work alongside the Scree. Still many restrictions on what humans are allowed to do or possess though. Earth is being turned into a Garden World, with all industries in LEO.
Somewhere in the region of a million humans were transported off to planet, being sold to the Drae slavers. Many died, but many more found ways out of slavery. Together with a few hundred humans who escaped from Earth before the Scree took control, they can be found throughout the One Time surviving as best they can. For many of them, Earth is a but a name - a memory of their parents. A few have done well for themselves, but most are living poorly.