"Despite the rather mind-boggling rate at which Earth is losing atmosphere -- 5×10^25 molecules per second -- scientists say there is no cause for alarm. If the loss rate stays the same, the planet's atmosphere will last for several more billion years.

"Ultimately we're trying to understand why Venus, Mars and Earth atmospheres behave so different when initially the planets were pretty much the same," Russell said.

Russell presented his research at the American Geophysical Union conference in Toronto last week. He and his colleagues are working on paper that details the comparative atmospheric losses of Earth, Venus and Mars."
http://dsc.discovery.com/news/2009/06/02/solar-wind-atmosphere.html
linked from http://wattsupwiththat.com/