Probing the `Dark Age' with NGST
  At redshifts between 5 and 20, stars and `subgalaxies' created the first heavy elements; these same systems (together perhaps with `miniquasars') generated the UV radiation that ionized the IGM, and maybe also the first magnetic fields. The history of the universe during this crucial formative stage is likely to remain highly uncertain until the launch of NGST. 
Martin J. Rees