Asteroid 2011 MD was part of a group of earth approaching asteroids called Apollo Class, which regularly crosses earths orbit and however unlikely have a slight but discernible chance of striking earth.
There is however a near earth asteroid discovered in 1951 Geographos if impacted earth would cause an extinction level event on the scale of the object that destroyed the dinosaurs. Albeit closer to our future we have the threat of asteroid Apophis to deal with, which is looming ever closer, mooted to either shave past or impact earth April 13 2036 several kilometers in diameter that would potentially cause severe devastation.
Its worth noting that Susan Sontag has said that "Science fiction films are not about science. They are about disaster, which is one of the oldest subjects of art."
The educative documentary video below from the Discovery channel encapsulates the mythology perpetrated by Hollywood with several speculated scenarios. The video rounds out its discussion of a possible utilization of near earth asteroid getting captured and turned into kind of box car facility for future inter solar activity.
