alien invasion sci fi movie magic, there was probably no real logic behind the ground being cold. it was just done to make it look neat, the people in the film could not figure what was going on, first a lightening storm and then that, very strange events were taken place that they could not figure out, basicly little red flags that they did not understand that something was up . but the movie goers knew what these ominous first signs were all about.
chris
PS I am more interested in why people clothes did not disintergrate from the aliens weapons I know why it was done simply to show there was nothing left but their clothes but it is funny to think about. they can blow up houses and cities, nuke entire armies but are powerless to destroy your Fubu shirt, Levis Jean and Nike's also I wonder, if you are completly covered from head to toes leaving nothing exposed would the alien beam bounce off of you???