英语听力：探索发现 科学新发现：我们的大气层-20（在线收听）

 As the balloons rise higer still,they face an attact by an invisible bombardment,radiation.Every day the Sun radiates a titanic amount of energy,some of them in the form of high energy of ultra violet rays.These rays packed a powerful punch ,and in the high up atmoshpere they attack the structures of the piles of balloon.The UV literaly damages the material,you start getting the microscopic cracks on the materials which makes a brindle and eventually just fails and the balloon pops.The rays are potential killers,both for balloons and human.They bombard our cells and DNA,triggering cancers.But around 7 miles up, a layer in the atmosphere shields us from 99% of this rays.It's made up of ozone,a rare monecule of three-bonded oxigen atoms.This can absorve and block high energy UV rays.The ozone layer is not like the saran wrap,thick layer the boundary that you past through.It's actually miles and miles thick,so it's a slow diminishment.Man made chemicals used in refregeraters and aerosols have been eating away this delicate protective layer.Every winter,holes in the shield appears in the poles.The harmful chemicals are now banned and the layer is beginning to recover.