Do you know what adobe is? It is a building material that is as old as the hills (not sure what the means) except that adobe has been around for many centuries and it is made of earth (like the hills).
It starts out as earth. Earth that is not too wet and yet not too dry. When people make adobe bricks the earth has to be just right.
Traditional adobe is a mix of earth, straw and horse poop. A more modern recipe for adobe mixes clay, sand, straw, and asphalt. The various elements do different things to bind the blocks together, creates strength and to avoid cracking. In the more modern way, the asphalt makes the bricks WATERPROOF. Isn’t that amazing?
A wonderful aspect of adobe is that it has zero-waste so it does not hurt the earth (unlike a lot of other building materials). Because it is made of stuff from the earth, all of the elements can return to the earth.
Adobe can be shaped into all sort of brick shapes for piling into walls. And when bricks break or crack, they can be replaced easily. Look at some of the interesting structures that have been made all over the world out of adorable adobe in this story in archdaily about adobe.