What kind of shape of a sanddune tell you about how it was formed?

Why does physical weathering speed up the processes of chemical weathering? a) physical weathering requires abundant water, as does chemical weathering. b) physical weathering produces fresh surfaces for chemical weathering to attack. c) chemical weathering can occur only on small surfaces, not large ones. d) chemical weathering requires salt, which is provided by salt wedging.

Which theory suggested that the earth was once a signle supercontient that gradually that broke up into the contients that we know today

Where does the availability of water pose the greatest problem