| Even Longer Records.... Evidence for these dry periods comes from paleoclimatic proxy data such as pollen, charcoal, minerals and other materials within lake sediments, and sand dune sediments. Fossil pollen data provide information about changes in vegetation composition, used to reconstruct past changes in precipitation and temperature. Relative changes in charcoal abundance, indicative of fire, are interpreted in terms of climatic conditions favorable to fire. Changes in the composition and the chemistry of sediments of lakes provide information on regional aridity and drought. Lake level records are a direct measurement of moisture balance providing information on long term hydrologic variability. The interpretation and dating of ancient soils and wild-blown sand/silt deposits constrain the timing and magnitude of sand dune mobilization associated with large-scale droughts.
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