I have a close business associate who literally spends thousands of dollars taking college courses to keep his mind sharp.
I don't make money at this, I consider it one of my volunteer activities because it is a subject I feel strongly about.
For me, the writing is secondary, I LOVE research. I will do all the research anyway so why not share it and continue to learn from others?
Having stated that I will also share it is possible to earn a living online. If you are good writer and IF you are dedicated and lastly if you find your writer's voice. By writer's voice, two items must be fundamental - you are passionate about your topic and you have a laser sharp focus.