Yeah, absolutely. It takes time and it takes a lot of hard work in the beginning. If you can get enough traffic onto a site daily, you can easily earn hundreds of thousands a month. Those sites are few and far in between but they do exist. If we are talking blogs only, I would look at buying an already established domain that is earning for itself and learn from it, replicate it, and make 3 or 4 blogs around the same base model. You will be earning in no time. If you work hard enough at it, you can see huge profits within the first 3 or 4 years.