An asteroid is streaking towards Earth.  Its exact path is not known … a solid strike or a near miss.  The people on Earth are alerted.  Governments plan to send up missiles to nudge the asteroid away from Earth.  It’s a glancing blow.  Debris is thrown into the atmosphere.  Earthquakes everywhere.  Volcanoes going off.  Destruction everywhere.  Chaos.  Earth enters a long ‘nuclear winter’ from all the debris in the atmosphere.  Huge losses of life.  Mankind adapts … rebuilds.