How many atmospheres fors the earth have?

1 atm or less unless you go underwater. 3 atm is about 20 meters in depth.

http://www.calctool.org/CALC/other/games/depth_pre...

One atmosphere is the air pressure at sea level (it varies a bit with the weather but that is the "standard" pressure).  the "3 atmosphere" rating usually means "3 more atmospheres of pressure above natural air pressure", and is usually done with reference to water resistance only.  Each 33 feet of water is about one atmosphere of pressure so the watch ought to take the equivalent of about 100 feet under water without leaking.  A good hammer strike will generally still smash the watch.  Static load is a different animal from kinetic or dynamic collision/impact in terms of force and capacity to resist the force. 

5

Exosphere

Thermosphere

Mesosphere

Stratosphere

Toposphere

Normal air pressure is approximately one atmosphere; that is where the definition comes from.

However, in relative terms, it's zero, as that will also be the pressure inside the watch.

A rating around 2 - 3 atmospheres on a match basically means "splashproof", not really enough even for swimming or continuous immersion.

In purely hypothetical terms it's equal to a depth of 30m underwater, but that does not account for the pressures caused by movement or flowing water, which can cause momentary pressure far beyond the pressure from depth alone.