It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth ( up to five kilometers below the surface ) in the form of extremophile archaea , rather than the better-known eubacteria ( which live in more accessible conditions ) . It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth , up to 5 k below the surface , in the form of extremophile archaea , rather than the better-known eubacteria ( which live in more accessible conditions ) .