Describe the planet earth from the perspective of an alien from another planet

  Your question is interesting, because I am not sure if the alien would be describing the planet itself or the inhabitants of Earth.  For argument's sake let's say that the alien is part of an exploration group.  The alien would look at the length of our day, our atmosphere, and plant and animal life.  The alien would also describe mineral resources and may even scout for possible landing and colonization sites.  Aliens would also look for samples of life to take home with them for further experimentation.  
Aliens would also comment on the most advanced species on the planet, which would be humans.  Were the humans friendly or dangerous?  Were the humans intelligent?  All of these things would be part of a useful description for future alien visitors.  When writing your answer, try to keep in mind the alien's reason for describing Earth.