Currently, there are two Unicode codepoints for symbols representing the Earth, used mainly in historical publications and contexts: U+2641 (http://unicode.org/cldr/utility/character.jsp?a=2641
) and U+1F728 (http://unicode.org/cldr/utility/character.jsp?a=1F728
An alternate character to the second one, used to my knowledge in the 18th and 19th centuries, was a circle with an equator line only. See for example this page from an 1872 high-school astronomy text (reference in the Wikipedia article on astronomical symbols): http://books.google.com/books?id=XksAAAAAYAAJ&pg=PA32#v=onepage&q&f=false
, where "a sphere and its equator" is given as one of the two symbols. Benjamin Franklin also used this symbol in Poor Richard's Almanac
, for example: http://public.gettysburg.edu/~tshannon/his341/pra53293.htm
(a little hard to see but starting 9 lines from the top of the right-hand page).
There are numerous glyphs in Unicode that look similar, notably capital '0' with a median bar, Greek capital theta, etc., but nothing I see that is a pure circle with a media bar (in U+29B5 it extends to the sides).
Would it be worth working up a proposal for this symbol?