When Google started they sold the platform based on better search results with an interface that didn't put advertiser content above organic results. Now you usutally don't see organic results without scrolling. When Google first started advertising, they didn't have the massive tracking network they have now. Advertising was based on surfacing advertising related to the terms you searched for and was often relevant to what you wanted.

They were profitable enough under that model to buy You Tube, Android, and many of the other services now under the Google umbrella. I would assume their business model would continue to be selling advertising based on relevant search terms.

Good answer, thanks!