If we should go by the term 'investment,' I think it's impossible to earn without any investment. Life doesn't work like that. The time dedicated to blogging itself is an investment. So I'd take the term 'investment' in your case to mean 'money.' And yes, you can earn with your blog without investing money into it except paying the hosting company. 1) Get a good, free themes and plugins. 2) Create mind-blowing contents that'll drive traffic to your blog. 3) Connect with influencers in the game by guest posting to their blogs. 4) Monetize your blog through affiliate programs whether Pay Per Click or Click Per Action. All these, of course, don't come with ease. You have to put in your best--time and efforts in order to earn. I hope this helps.