How about mining? Isn't that a way of earning? Sorry for a naive reply, I am just a newbie who wanted to learn and interested in this question. 
You can do mining there is many ways to do that if you want free investment you have to do task like join in free mining cloud that offer free.and if you want to do mining at your own, it cost you money first to buy equipment for mining,or you invest legit mining online like genesis mining etc.