A branch of paleontology dealing with the fossilized microscopic organic remains (microfossils) of the geologic past, their structure, biology, phylogenetic relations, and distribution in space and time. The study of these microfossils has become an independent scientific field largely because of the following: (1) The size of these fossils requires special methods for collection and examination. (2) Their abundance in geologic formations makes it possible to analyze their spatial distribution and the rates of morphological changes during the course of evolution by means of statistical methods which can be used only under exceptional circumstances in the study of larger fossils. (3) Microfossils have become indispensable tools in certain branches of applied geology, especially in the exploration for oil-bearing strata, because countless numbers of these minute fossils may be obtained from small pieces of subsurface rock recovered from drill holes. (4) The diversity of microfossils, their wide spatial distribution in varied environments, and their distinctive steps in evolution and the ease of studying them have contributed to make micropaleontology one of the most actively studied branches of the earth sciences. Many organisms are restricted to certain environments best suited to their life activities. The occurrence of certain organisms in sediments, therefore, can in turn provide a clue to a particular environment that existed in the past. Micropaleontologists can obtain important information about depositional environments, such as their ancient environment, water depth, temperature, current systems, water mass distribution, proximity of shore lines and, of course, these organisms are used to date ages of enclosing sediments.