New Australia

Prisons Ministry looked at Gate Technology and dreamt of a New Australia.
“The parallel universe is habitable,” said the Warden-General. “Just like Prehistoric Earth. Better there than wrecking civilization here.”
The test prisoners went through without problem, surviving the trip and living out their lives peacefully across the Gate.
Approval was given, and prisoners were shipped off by the hundreds.
Eventually the world treated the Gate as their social garbage disposal. Murders. Rapists. Thieves. Tax cheats. Jaywalkers.
Until one day, research determined that they actually were going into Prehistoric Earth.
And they were hunting Homo habilis for sport.
Civilization vanished.