Diatoms are identifiable based on each species unique silica cell walls and vary depending on their environment. Because they have determinant properties diatoms create flora profiles for scientists. When these microscopic algae die, their frustules (silica cell walls) becomes a part of the water sediment. The presence of the frustules enables scientists to compare the cell walls of the deceased organisms with the living diatoms to determine characteristics of their environment. In early spring and the fall the ratio of living diatoms to dead diatoms is high, whereas, in summer and winter the amount of dead diatoms outpopulates the living. Based on this known information diatoms can verify the time of year samples were taken.