This isn't an earth floor but it had a lot of earth in it. It was our very cheap but very time-consuming alternative to expensive terre cuite tiles. I thought about an earth floor but I dye wool and make a lot of conserves and we have some older dog/cats and sometimes lambs and kids who pee on the floor occasionally, so it was too much of a risk to try an earth floor, then have to redo it because it couldn't stand up to the humidity.
I read how to use straw for insulation under the floor and make the tiles in a book called "The Straw Bale House". So on top of about 75cms of rocks, we laid straw bales with mortar mixed with straw between them to support the floor. The floor is warm in the winter and cool in the summer. On the left in the photo is a small underfloor cellar which stays really cool.
Then we laid a classic screed floor and on top (because our house is bioclimatic and we wanted loads of thermal mass) we made a mix with sand, clay, white cement and ochre colours and made "tiles", tamping them down, then cutting and shaping them by hand (plastic bag over hand) to consolidate the mix and give them a nice finish.
Finishing off the last joints between the "tiles"
Floor after 17 years (Although I promised to wax it every summer, I don't) I love the floor and it doesn't show the dirt much with loads of muddy boots and 5 dogs coming in and out.