Does reach blow up IN HALO?

Answer 1

It wasn't exactly blown up. It was glassed, but not in the normal way, either. Glassing is sending streams of plasma down on a planet, and the heat created wipes out most life forms on the planet, sometimes making material (including organic material) into glass, hence its name.

However, Reach was a bit different.

The covenant detected forerunner artifacts on the planet, so they didn't completely glass the planet, as they were afraid completely glassing the planet would destroy the forerunner artifacts they held so dear. They only glassed the major military sights, leavinglarge pockets of life on Reach.