Mary Ann Woerner, age 12, of Tremont, Ill., for her question:

 How do salt flats form?

A salt flat stands on the dried out floor of some ancient sea or old inland lake, of salty seawater. In the past, the seas have invaded vast areas of the established continents many times and receded back to their basins. In some places, stretches of soggy salt marsh have been lifted high and dry, and in other places arms of the sea have been sealed off from the ocean by landslides.

These geological events often left salty lakes and large puddles of seawater to dry up in the air. The evaporating water did not carry aloft its loads of dissolved chemicals. These salty solids were left behind in flat layers on the floor. The lane areas left behind after all the water was gone were salt flats covered with crusty layers of the salty chemicals once dissolved in seawater.