this is what i think happened....
meteor comes to destroy the planet,but it only comes to destroy anything that is harmful to the planet if im not mistakin...but Nanaki and his tribe of people were the planets protectors, therefore he would not perish......and so then,after being the only one left on the planet for say, 200 years, the lifestream kicks in and starts reproducing all the energy in the planet in the form of vegetation and Nanaki's clan...this is just what i think,plz beg to differ