The removed core is sampled every 10 to 20 cm and washed in solutions of very strong, corrosive chemicals, such as potassium hydroxide, hydrochloric acid, and hydrogen fluoride. This harsh process removes the organic and mineral particles in the sample except for the pollen, which is composed of some of the most chemically resistant organic compounds in nature. Microscope slides are made of the remaining pollen and examined to count and identify the pollen grains. Because every plant species has a distinctive pollen shape, botanists can identify from which plant the pollen came. Through pollen analysis, botanists can estimate the composition of a lake area by comparing the relative amount of pollen each species contributes to the whole pollen sample.
Carbon dating of the lake sediment cores gives an approximate age of the sample.
Scientists can infer the climate of the layer being studied by relating it to the current climatic preferences of the same plants. For example, they can infer that a sediment layer with large amounts of western red cedar pollen was deposited during a cool, wet climatic period, because those are the current conditions most conducive to the growth of that species. First, by examining the pattern of plant changes over time, they can determine how long it took for plant species to migrate into or out of a given area due to natural processes of climate change. This information makes it easier to predict the speed with which plant communities might change in response to future climate change. Second, by determining the kinds of plants that existed in an area when the climate was warmer than at present, scientists can more accurately predict which plants will be most likely to thrive if the climate warms again.