Micropaleontology is the study of microscopic fossils. It is the largest discipline in paleontology, just as microfossils are by far the most abundant of all fossils. Although nearly invisible, micro-organisms at the base of the food chain make up nearly 90 per cent of the biomass in oceans and lakes. The variety of life forms at this level is almost incomprehensible, and while only a few kinds leave solid remains that fossilize, even these few can be so abundant that in places they form mountains of pure fossil remains. The limestone of the plateau from which the Sphinx and Pyramids are carved is actually a mass of foraminifera (left, in a microscopic view), preserved in a vast offshore formation that, 40 million years ago, extended from France to Burma. The Chalk Cliffs of Dover, another microfossil marvel, is a layer hundreds of feet thick all across western Europe that consists of nothing but sub-microscopic coccoliths (see below). In other parts of the world, solidly packed remains of diatoms (see below) make up formations of thin-layered diatomite hundreds of feet thick that are quarried for industrial uses.

The abyssal floor of the ocean, which occupies more than half of the earth's surface, is buried under a carpet of microfossils that slowly piles up like layers of dust over the millenia. Changes in the abundance and types of microfossils from year to year, over millions of years of undisturbed accumulation, makes an exquisitely detailed record of climate change, plate tectonics, and biological evolution. Each time a new species of free-floating marine micro-organism (such as the dinoflagellate, right) evolves, it quickly spreads throughout the oceans in countless billions, forming a worldwide marker in the fossil record. Such marker horizons allow geological events in different parts of the world to be related in a global earth history. For instance,it was the microfossil "tape recorder" that proved that reversals of the polarity of the earth's magnetism were worldwide events. Microfossil data also revealed that changes in sea levels, temperature, and glacial advances were synchronous worldwide, proving the reality of global climate changes more accurately than geochemical dating methods.Recently, micropaleontology has shown how oscillations in the earth's orbit and tilt lead to cycles in global climate, including the Ice Ages.

Microfossils are vital to oil exploration. Because of their tiny size and great abundance, they occur unbroken in the rock fragments brought up by drilling into the deeply buried ocean formations and lake beds where oil is found. By comparing the characteristic fossils from each formation as they are penetrated by the exploratory drills, geologists can unravel the geometry of the strata far beneath the surface and locate the domes and traps that may hold oil. The condition of the fossils, as well, indicates whether the petroleum source rocks have been buried and heated sufficiently to generate oil from trapped organic matter. Most importantly of all, the organic matter itself is almost entirely from ancient micro-organisms that make up the ocean's biomass. (Diatoms, as at left, are important trace fossils as well as the primary source of oil.)

Most of the principal microfossil groups are Protista. These are single-celled or colonial Eukaryotes (i.e. organisms with cell nuclei and chromosomes), that are more advanced than Prokaryotes (archaea and bacteria), while being ancestral to higher eukaryotes such as fungus, plants and animals. The foraminifera and radiolaria are two orders of predatory (i.e., non-vegetative) protists, related to amoeba in the Sarcodina, that secrete multi-chambered limy and siliceous shells, respectively.

Vegetative (photosynthesizing) protists with fossilizing hard parts include coccoliths, with complex structures (as in the coccolith at the right, and on our splash panel ) that break down into submicroscopic but readily identifiable limy disks and stars, and the diatoms, with single-chambered circular or ovoid valves of silica that fit together like pillboxes. The dinoflagellates and their extinct relatives acritarchs, with whip-like propulsive flagella and chitinous body casing, are both predatory and photosynthesizing; they are represented in the fossil record by the cysts that they make during one part of their life cycle.

Important groups of microfossils are also found among animals and plants, for instance the ostracodes, tiny free-swimming crustaceans in the same family as barnacles. Spores and pollen from fungi and plants give important paleonvironmental data. In ancient strata conodonts, the teeth of an extinct group of soft-bodied invertebrates, are important stratigraphical guides, and icthyoliths, or fish teeth, are used for deep-sea dating.

Recommended reading covers the biology of microfossils and their role in unravelling the history of life and the great geological events that shaped the modern oceans and continents.