I think that google earns from ad network - Adwords and adsense. Almost all people using adwords to promote their business online.
too many options are provided by Google search adsense, adwords, Google applications analytical tools
Advertising is the main earning source of Google. Millions of companies are spending billions for advertising on Google.
Given that Google Adsense pays money out to people that is not how Google makes money. Google Adwords is where they make money, as in people pay to advertise. Adsense is what Google uses to buy advertising to sell the advertising it sold for Adwords
It is simple to understand from this chart, Check this out. http://static6.businessinsider.com/...-of-the-day-google-search-profit-oct-2010.jpg