Earth is properly capitalized. It is a proper noun -- the name of the planet.
I was lost in the second paragraph of the article, but the posts have been a great read. It has been a fascinating debate on the finer points of physics.
I love this place.
Earth:
It is lowercase unless at the beginning of a sentence. That would be according to Webster's. Moon is also lowercase, as is sun, universe, world. For proper names we usually resort to Latin and use Terra, Luna, Sol, etc., and then the names are considered proper names and capitalized. It may be used with or without the definite article, as in earth, or the earth. It is sometimes capitalized anyway, depending on whether your English teacher insists.