A dramatic fact was found from the peat bog in the Easter Island whose civilization has remained in a fog of mystery. By identifying the pollen grains in the sediment, the real picture of the past environment and the people's lifestyle were held among the researcher's minds. The island was covered by forest, rich in the varieties, animals and fresh water. The people who lived there could get everything they needed from the gifted forest. However, the civilization had disappeared since they had used up the resources by cutting trees and indiscriminate hunting. All the vegetation was gone.

The pollen analysis, study of vegetation history using the microfossils (pollen grain and spores of size 15-50 um), can give us useful information about the target area's condition in the present and past. Since the outside of the pollen grain wall is made of highly resistant material, the pollen spores from 400 million years ago can be found today. Each pollen grain and spore is different in structure and shape, thus, the morphology is the key to understanding the kinds of vegetation that existed and their evolutionary development.

When we think of the lakes created by the glaciation some 12,000 years ago (most lakes in Minnesota), the sediments within the lake have been deposited about 12m thick. By making a bore hole in the sediment, a vertical sequence of sediment can be drawn, each of which have been deposited at a particular time in a particular sequence.

Each sample can be analyzed for pollen grain and spore content, with each grain or spore being identified as the prepared slide is traversed on a mechanical stage under the high-power microscope. Then a pollen diagram, graphical expression of pollen analysis, can be constructed with consideration of sampling error.

Analysis of this kind were first produced by the Swedish geologist Von Post in about 1916. From the pollen diagram, information can be obtained about vegetational, floristic and climatic changes (sea levels, too) which took place in the past. The difference in amount of pollen in 1cm cubic tells us the condition of the forest. If the amount is small, it could be tundra (moss), and larger amounts indicate deciduous forest (vegetation which depends on pollen or spore reproduction.) As studying the pollen analysis, researchers have to deal with many aspects such as, wind direction, vegetation identification of surrounding areas, pollen traveling distance, lake sedimentation, turn-over rate of the lake ecosystem, etc.

The analysis are based on statistical correlation and probability. To get a reliable conclusion out of the complex phenomena, the researchers try to improve the accuracy by adding new technology, such as computer and carbon dating technique.

Reference

West, R.G. Studying the Past by Pollen Analysis. Oxford University Press 1971.