There have been many paleolimnological studies done to determine past general productivity via the stratigraphy of chlorophyll and carotenoid degradation products in sediments. Morphological remains of many plants and animals are fossilized in lake sediments. Most lakes are less than 20,000 years old, geologically this is young. If the modern physiology and ecology of the organisms are known one can make predictions about past ecological conditions. Plant pollen and spores are often used to help make these predictions.
Pollen grains are the tiny male reproductive bodies of flowering plants.
Their outer shell is indestructible and can survive in certain sediments for tens of thousands of years. In pollen analysis the exines or shells of pollen are taken from the soil and studied underneath the microscope. At this time identification is done according to the distinctive shape and surface of the exine. Once all the information is quantified, the identifications are plotted as curves on a pollen diagram. Fluctuations in the curve for each plant category may indicate signs of climatic changes or forest clearance and crop planting by humans.