run the evolution of the planet to see how it looks 
        after 'years'

def evolve(self, years):
        """
        run the evolution of the planet to see how it looks 
        after 'years'
        """
        world_file = fldr + os.sep + self.name + '.txt'
        self.build_base()
        self.world.add_mountains()
        self.add_life()
        self.world.grd.save(world_file)
        
        print('TODO - run ' + str(years) + ' years')