Question

what is the earth mean temperature? state it's one advantage

Answer 1

The average temperature on Earth is about 61 degrees F (16 C). But temperatures vary greatly around the world depending on the time of year, ocean and wind currents and weather conditions. Summers tend to be warmer and winters colder. Also, temperatures tend to be higher near the equator and lower near the poles.  
SIMPLE Answer is 

The Earth's mean temperature is 17° C. Because of that life is possible.