What is the average temperature of the Earth today?and What was it when earth was starting out (4BYA)?

Answer 1

the average temperature annually for the planet (not today) is about 15C, on the land surface. THe average for England is 10C if your interested, dont know about america because is so overproportionaly big for a country, should be a continent.
oh yea, 4bya most of the planets surface would still consist of molten rock, although we were still a similar distance from the sun, there was still a huge amount of heat and energy left over from the big bang, which can still be found today in the earths core. as a guess the temperature would have to be several thousands of degrees

Answer 2

Tough question because the thermometers were so primative back then and global waming today, but it is generally felt that because the earth was closer to the sun and because of increased radioactivity and energy from impacts of space materials, it was much hotter than now. At some point, it had to be hot enough to melt some of the granite rock that forms the base layer of the continents (say 2000C) and some time later it had to be cool enough for water to condense (so under 100C)