Most animal groups populating our planet today appeared during the early Cambrian (by about 520 million years ago), establishing the animal-rich biosphere we still have today. Despite the biological importance of this time, there are still substantial uncertainties about what Earth was actually like then, in particular the position of the continents and the nature of the climate. These uncertainties persist because most of the techniques used to reconstruct past climatic conditions and to determine the palaeo-positions of the continents are difficult to apply so far back in time. In particular, the further back in time we go, the less rock is preserved, and more likely it is that the physical and chemical properties of the preserved rock will have been altered by geological processes.