The interpretation of these features of the cosmic ray spectrum depends on the details of the model assumed.Historically the ankle is interpreted as the energy at which the steep Galactic cosmic ray spectrum transitions to a flat extragalactic spectrum. However diffusive shock acceleration in supernova remnants, which is the predominant source of cosmic rays below 10 eV, can accelerate protons only up to 3 x 10 eV and iron up to 8 x 10 eV. Thus there must be an additional source of Galactic cosmic rays up to around 10 eV. On the other hand, the 'dip' model assumes that the transition between Galactic and extragalactic cosmic rays occurs at about 10 eV. This model assumes that extragalactic cosmic rays are composed purely of protons, and the ankle is interpreted as being due to pair production arising from interactions of cosmic rays with the Cosmic Microwave Background (CMB). This suppresses the cosmic ray flux and thus causes a flattening of the spectrum. Older data, as well as more recent data from the Telescope Array do favour a pure proton composition. However recent Auger data suggests a composition which is dominated by light elements to 2 x 10 eV, but becomes increasingly dominated by heavier elements with increasing energy. In this case a source of the protons below 2 x 10 eV is needed.