It's finally happened. After several years of dominance, Microsoft's Web-based email service, Hotmail, has been unseated by Google's significantly younger webmail service, Gmail.

Gmail's growth has skyrocketed since its public introduction in 2007, but this year in particular, Google has been successful in attracting millions of new users. In January, Google mentioned in its earnings call that it had about 350 million monthly active users on Gmail; six months later, about 75 million more users had flocked to Gmail, growing the total number to 425 million monthly active users. By this measure, Gmail has dethroned Hotmail.

A few notes to mention: Gmail has more monthly active users than Hotmail, but comScore mentions that Google has significantly fewer unique visitors than other rival email services. Hotmail currently sits at No. 1 with 325 million unique visitors, Yahoo takes the No. 2 spot with 298 million users, and Gmail comes in at No. 3 with 289 million users. But while Gmail is still behind in these areas, it will catch up shortly; the other services had a significant head start. Hotmail was launched in 1996, Yahoo Mail was launched in 1997, and, in comparison, Gmail was only created eight years ago in 2004.

This is the circle of life with email services: AOL Mail and Yahoo Mail both had their days in the sun, but both were eventually overthrown by newer mail services like Hotmail and Gmail, which promised more useful, intuitive features than their precedessors offered. Now, Google appropriately gets to claim it's the top dog in the webmail contest, as most of the company's products have become dominant in each of their respective areas. In search, Web browsers, email services, hardwaresoftware, and beyond, Google has been dominant over the last decade. Gmail's rise to the top is a tribute to Google's elevated status overall in terms of global digital culture.

Google has surpassed Microsoft in Web browsers -- and now email services. It's clear that the two top tech companies in America are currently Apple and Google, no longer Apple and Microsoft. Given the products and software services announced at Google I/O this week, it looks like Sergey Brin and crew have no intentions of letting up.