does pure water boil at hundred degrees everywhere on earth?

No. Water boils at 100 deg Celsius at sea level. At higher elevations, water boils at lower temperatures. 

Boiling begins at the point when a liquid begins to vaporize (turn into a gas). This can only begin to occur when the vapor pressure of the liquid is at least equal to the surrounding air pressure.

Air pressure decreases as elevation increases, so less vapor pressure is required before vaporization begins. Vapor pressure increases with increasing heat. So this results in lower boiling points. 

Conversely, water boils at higher temperatures below sea level, because the air pressure is increased. 

It is important to note that it is not just water that behaves this way. All liquids will experience different boiling points at different physical elevations.