I don't think you can earn free bitcoin, all those site that will ask you to be minning bitcoin for free, all of them are scam, no free way to get bitcoin, if you can't invest or work before you get paid, then nobody will give you bitcoin for free, most of those minning sites are just scam, they just want to take steal from you, or some might ask you to drop your wallet address on a site then you will receive free bitcoin, all of them are scam, if you are looking for free money in Cryptocurrency space then you might endup being scammed, we all have to be smart, Bitcoin is too precious than to be sharing it for free.