Earth can be a very good material to build with. Very little energy is needed to extract, transport and use locally quarried sub-soil, and so the carbon emissions that result from its use will be tiny when compared with brick or concrete. Unfired earth can also be easily reclaimed at the end of a building's life.
There are different ways of using earth in building; most have a very long history. We have used rammed earth here at CAT, in our information centre (opened in 2000) and in our new WISE building (the Wales Institute for Sustainable Education). We also used compressed earth bricks to build a toilet block. A method used traditionally in the south-west of England is cob building - a mixture of earth and straw.
You can read more about these various techniques in this article about earth construction. It was written by Cindy Harris, co-author of the Whole House Book, for the CAT membership magazine Clean Slate.