What is the average temperature of the Earth?

Dasht-e Lut desert, by http://picasaweb.google.com/kispoev

Question posed by Ciara

That all depends on what you mean by 'the Earth':

If you're talking about the Earth's surface, the bit that's most immediately important to use because we live there, then the average temperature is, depending on which sources you look at, usually said to be somewhere between 13 and 17 degrees centigrade. Quite comfortable for us, which makes sense!

There is quite a wide variation in temperatures, however: The coldest temperature ever recorded on Earth was at the Russian Vostok weather station in Antarctica on 21^st July 1983 - a rather chilly -89.2 °C (or 184 K). The highest recorded temperature on Earth was in the Dasht-e Lut desert in Southeastern Iran, which reached a whopping 70.7 °C (that's 343.85 K) in 2005.

Vostok station, Antarctica, from http://www.newzeal.com/

If you want to include the entire Earth rather than just the thin layer that we live and breathe in, then the story's a little different. Temperature estimates of the Earth's core hover around 7000 °C in the middle, and drop to around 4000 °C in the outer core. The mantle, the area between the outer core and the Earth's crust, is thought to be around 870 °C. These regions take up a much larger volume of the total Earth, so estimates of an average temperature for the entire body would be much greater than the 15 or so degrees given above; we're looking more towards the thousands!