Palynology is the study of organic (i.e., non-mineralized) microfossils, especially those in sediments, either of terrestrial (land), freshwater, or marine (sea) origin. These microfossils are very small, generally falling into the 5 - 500 µm range, and are found in rocks of all geological ages, beginning about 1.4 billion years ago in the late Precambrian Eon right up to the present. Most palynomorphs are produced by plants, including flowering plants, such as apple trees and dandelions; coniferous plants, such as pine trees; and other plants, such as ferns and mosses, and some algae. Some are derived from fungi or from animals, such as the mouthparts of marine annelid (segmented) worms, which are called scolecodonts. Others are derived from dinoflagellates, meaning "whirling whips", which are types of mainly marine algae. Dinoflagellates are strictly neither plants nor animals but are members of another natural kingdom, the Protista. Further back in the geological record, there are palynomorphs whose biological affinities are uncertain. These include chitinozoans, which disappear by the end of Permian Period, about 250 million years ago, and which may have been produced by extinct life-forms called graptolites, and acritarchs, which are the oldest palynomorphs and whose very name means "of doubtful origin"!
The most widely-studied group of microfossils are pollen grains and spores produced by plants. This sub-field of palynology is often called pollen analysis. Pollen grains and spores are about the same size, are dispersed and deposited in similar ways, and are often found together. For these reasons, "pollen analysis" refers to the study of both. Pollen analysts look at material from the geologic past and also the production and distribution of pollen and spores today.
Palynology has wide application in the earth and natural sciences. For instance, it can be used to correlate (match) and provide relative ages for layers of rock, mainly in oil exploration (stratigraphic palynology), and to understand vegetation distributions (biogeography) and climate changes of the past (palaeoecology), especially in the Quaternary Period. As in the example above, it can be used to investigate what plants were available to people living in past landscapes (archaeopalynology or geoarchaeology). Palynology is also used to monitor the production and dispersal of pollen in the atmosphere (allergy studies or aerobiology), to confirm the type and purity of honey and its country of origin (melissopalynology), and, in recent police work, to trace the origin of illegal drug shipments (forensic palynology).
The oldest palynomorphs are found in Precambrian sedimentary rocks. Palynologists believe that these were probably produced by simple aquatic algae. Palaeobotanists think that the oldest terrestrial (land-living) plants appeared in the late Ordovician Period, about 440 million years ago. The spores produced by their descendants are abundant in rocks from the Ordovician to the Devonian Periods. Many of these types of plants, such as ferns and horsetails, still exist today. Spores are produced as part of their reproductive cycle and can be thought of as a type of primitive seed.
Pollen-producing plants first appeared in the late Devonian Period, about 360 million years ago, and have become the dominant plant type over most of the earth. The earliest types of pollen-producing plants were gymnosperms (which means literally "naked seed"), of which the best-known modern group are the conifers, such as spruce and fir trees. Flowering plants, or angiosperms (meaning "enclosed seed" plants), first appeared somewhat later, about 120 million years ago in the early Cretaceous Period. Because these plants have become increasingly abundant and diverse from the Devonian Period to the present, pollen grains have become more dominant in the geologic record and spores have consequently decreased in abundance. In most modern samples, for instance, pollen grains generally form more than 95% of the sample.
Many coniferous and flowering plants produce vast quantities of pollen as part of their reproductive cycle. Pollen grains carry the male genetic information for fertilization. From this, seeds are formed which ultimately can produce new plants. Pollen grains are dispersed widely over the landscape, mainly by wind, and are a major cause of the hay-fever and allergies suffered by many people in the summer months. Plants produce many more pollen grains than are actually used in reproduction. Much of the pollen falls to the ground or is washed from the atmosphere by rain and ultimately becomes part of sediments, especially the mud accumulating on the floor of lakes. Because pollen grains are so tiny, less than a teaspoonful of sediment can contain many thousands of them. Most pollen grains are extremely resistant to decay and are preserved in large numbers in many types of sediments.
Pollen grains have distinct shapes and surface patterns that allow palynologists to identify them according to the plants that produced them (Pictures 1 and 2). The walls of pollen grains are made from sporopollenin, one of the most resistant natural chemical substances known. This explains why the grains preserve so well and are still found relatively intact and identifiable after thousands or millions of years burial. Many grains are quite beautiful, with intricate textures and shapes. One of the great pleasures of palynology, and a source of constant wonder, is looking at all these tiny but perfectly-formed grains under the microscope. A small amount of lake mud may contain pollen grains from up to thirty to fifty different types of plants. When analyzing pollen from the recent past (the Holocene Epoch), palynologists assume that pollen grains were produced by the same plants that produce similar grains today, i.e., that there has been little evolutionary change over this time. Palynologists assume that these plants had the same climatic and ecological tolerances as their modern descendants. They can use this information, therefore, to reconstruct past climate and landscape conditions.
Quaternary palynologists usually work on cores of lake mud or peat, or sometimes cores from the sea-bed. This material is not usually hardened to rock, but is soft muddy sediment. Small samples of sediment taken from intervals throughout the core are separated and chemically processed to remove all the material except the resistant pollen and spores. Processing is done with relatively simple laboratory equipment but must be carried out carefully, not only to avoid sample contamination but also to avoid injury to the processor because some of the chemicals involved are dangerous. Palynologists may spend many hours in the laboratory to "clean up" or process a sample to extract the palynomorphs, which are concentrated into a residue. Tiny amounts of this residue are mounted on glass slides and, using a microscope, the pollen grains and spores on them are identified and counted. These data are then used to reconstruct a picture of the vegetation growing in the region around the collecting site. This stage of the work is like a detective story, piecing together information from the plants and other geological evidence to produce a picture of a vanished world - a snapshot of the past. The basic tool of the palynologist is the standard biological microscope but some palynologists, especially those interested in pollen taxonomy, use more powerful tools, such as scanning electron microscopes (SEM), which have much greater magnification.
Because sediments in a lake build up over time, the sequence of samples from the bottom to the top of a core provides details of vegetation change over time. In Canada, for example, we can use pollen analysis to trace the revegetation of the landscape following the end of the last major Ice Age from about 18,000 years ago to present. Plants often have very specific climatic requirements and tolerances and so knowing what plants were growing in an area at a particular time also gives information on the climate. Using this method, for instance, palynologists deduce that there was an interval of warmer and drier climate than today on the Canadian prairies about 9,000 to 6,000 years ago when the Prairie grasslands expanded northwards and many lakes dried up or became very saline (salty). This type of information is valuable for predicting how today's plants will respond to continued climate warming in the next few decades (Global Change).
As in the opening example, much of this research is multidisciplinary and involves collaboration with scientists from other fields. Combining information from many different disciplines allows a more complete picture of past landscapes to be built up. For example, palaeolimnologists may study other microfossils, such as diatoms, in lake sediments, geochemists may study the chemical composition of the sediments, especially salinity changes, sedimentologists may be interested in the changes in amount and type of sediment deposited in the lake over time as a measure of erosion in the catchment, and archaeologists may investigate the human occupation of the surrounding landscape.
Although naturalists have investigated pollen grains since at least the eighteenth century, palynology has only really developed as a branch of earth science since the 1930s. This was encouraged by the development of laboratory processing techniques allowing palynomorphs to be extracted from rocks. Growth was also stimulated by the application of palynology in oil-exploration following the Second World War, and the increasing attention being paid to environmental issues, such as Acid Rain and Global Change, in the last twenty years. Although it is lessening, there is a regrettable but real split in the discipline between primarily geologically-trained and primarily botanically- or ecologically-trained palynologists. With some exceptions, this very roughly corresponds to a division between stratigraphic and Quaternary palynology.
Stratigraphic palynologists, who generally have a background in geology, are usually concerned with pre-Quaternary rocks and often use palynology as a relative dating and correlation tool. Stratigraphic palynologists usually examine palynomorphs from rock samples from drill cores that may be many hundreds of metres in length. These ancient rocks may also contain other larger fossils, such as leaves or wood (studied by palaeobotanists) or faunal (animal) remains (studied by palaeontologists). When layers of rock are buried deeply, they are subject to great pressure and heat. This causes alteration, especially colour changes, in palynomorphs in the rock. These colours give palynologists valuable clues about the thermal history of the rocks which are useful for assessing the type and quality of any associated hydrocarbon deposits (coal, oil, and gas). Stratigraphic palynologists cannot assume that the palynomorphs they find are derived from the plants that produce similar pollen or spores today. On the scale of millions of years, evolutionary change has occurred. In fact, many of these pre-Quaternary palynomorphs are unlike any modern forms (Picture 3).
Traditionally, stratigraphic palynology has been a powerful tool in oil-exploration. Palynologists and biostratigraphers have correlated rock layers (strata) from different drill cores and assessed the origin (terrestrial or marine, for instance) of the sediments. Using all this information, petroleum geologists (Link?) can better understand the layering (stratigraphy) and the structure in the underlying bedrock and work out where would be the best place to drill for oil.
In the boom years of the 1970s, many stratigraphic palynologists found employment with oil companies. Unfortunately, in recent years the Canadian oil-industry has declined due to falling world oil prices and, as a result, oil-company-based palynologists in Canada have been laid-off. Most stratigraphic palynologists now work as consultants or in universities.
Quaternary palynologists often use palynology to investigate palaeoecological questions and to trace climatic and vegetation change. With increasing attention paid to these fields, there has been a "data explosion" in Quaternary palynology in the last few decades. In North America, palynological information from many different sites is gradually being compiled into large electronic databases. This allows palaeoecologists to ask complex questions about vegetation patterns and processes on a regional or continental scale, such as "How did plants migrate back into Canada after the last Ice Age?" To take full advantage of these new opportunities, modern palynologists need to have a good understanding of statistics and other computational methods, and require computer skills. Most Quaternary palynologists have a background in botany, biology, or geology (including physical geography and geomorphology). The application of palynology to topical problems, such as biodiversity and Global Change, suggests that this will remain an exciting and viable field for some time.
Fieldwork is an important part of palynology, as it is in all earth sciences, and a liking for the outdoors, including camping and hiking, are definite requirements. Fieldwork can involve rough or uncomforable conditions. Some palynologists may be involved in ocean-drilling projects, requiring them to spend time at sea. In Canadian Quaternary palynology, fieldwork often takes place in winter when it is relatively easy to core the mud at the bottom of the lake from the frozen lake surface (Picture 4).
However, unlike many other branches of earth sciences, fieldwork forms a comparatively small amount of the time required by any palynological project. By far the majority of time is spent in the laboratory, processing samples, working at the microscope, and analyzing the data (Picture 5). Meticulousness and patience are two essential attributes for a palynologist! Perhaps because of this emphasis on laboratory work, gender has not been such a great barrier to participation in palynology and the subject has attracted more female researchers than many other branches of earth science. Indeed, several of the outstanding palynologists working in North America at present are female.
Most palynologists in Canada work in university Botany or Geology departments, with government agencies, such as the Geological Survey of Canada, or with museums, such as the Provincial Museum of Alberta. Some work as private consultants, especially to the oil industry. However, there are comparatively few palynologists working in Canada. The main professional organization, the Canadian Association of Palynologists, for instance, has only about 60 members, of whom 12 or 20% are female. Salaries for palynologists are modest, compared with other branches of science. The main motivation for going into the field is not financial but, rather, an intense curiosity about the past development of the landscape we see around us everyday.
Educational requirements: PhD, generally from a Botany or Geology department.
Starting salary (as a junior faculty member in a university department): about $35,000/year. Note that many palynologists work for years in Postdoctoral positions, as sessional lecturers, or on various types of research contracts, all of which pay much less, before obtaining more stable full-time employment.
catchment = the area surrounding a lake that drains into that lake.
core = a core is a cylindrical sample of rock or mud. Cores can be obtained with simple hand-operated corers or machine-driven drill-rigs. Most soft-sediment cores obtained from hand-operated corers are only about 6 cm in diameter. Rock cores from drilling may have a somewhat larger diameter.
Cretaceous Period = an interval of geologic time, roughly spanning 144 to 65 million years ago.
Devonian Period = an interval of geologic time, roughly spanning 410 to 353 million years ago.
diatoms = diatoms are a type of algae which produce a structure made from silica that is often preserved in great numbers in lake sediments. Diatoms are roughly the same size as pollen but their remains (called "frustules"), being formed from silica, are usually destroyed in the chemical procedure to extract pollen from sediments. A separate, different preparation technique is required to extract diatoms from sediments.
Holocene Epoch = an interval of geologic time, the last 10,000 years, the time since the last major ice-age in Canada.
µm = micrometre. There are 1000 micrometres in a mm. So 500 µm, about the size of the largest palynomorphs, is 0.5 mm.
Ordovician Period = an interval of geologic time, roughly spanning 510 to 441 million years ago.
palaeolimnology = limnology is the study of lakes, so palaeolimnology is the study of lakes in the past.
palynomorph = literally, "a pollen-shaped thing". A general term used to refer to all the material studied by palynologists whatever its origin.
Permian Period = an interval of geologic time, roughly spanning 300 to 250 million years ago
Precambrian Eon = a vast interval of geologic time, stretching from the formation of the Earth, perhaps 4.6 billion years ago to 544 million years ago. The first primitive forms of plant and animal life appeared towards the end of this interval, in the Proterozoic Period, between 2500 and 544 million years ago.
Protista = kingdom of one-celled organisms. The protists are one of the five major subdivisions into which all living material is classified. The others are plants (Kingdom Planta), animals (Kingdom Animalia), fungi (Kingdom Fungi), and microbes, including bacteria (Kingdom Monera). Many members of the Protista have characteristics that are intermediate between plant and animal, or have affinities of both. All Kingdoms, except Monera, produce palynomorphs.
Quaternary Period = an interval of geologic time, equivalent to the last 1.7 million years.
sedimentary rocks = rocks that are layered, built up from smaller particles such as sands, silts and clays. This category also includes rocks that have been derived from solutions, such as rock salt, or built up from the accumulation of organic material, such as coal.
Silurian Period = an interval of geologic time, roughly spanning 441 to 410 million years ago.
taxonomy = classification and naming of organisms
1. A pollen grain from lodgepole pine (Pinus contorta). This pollen type has bladders which give it buoyancy. It is dispersed far from its parent plant by wind. Therefore, pine pollen can often be collected in areas far from any pine trees, such as in the Arctic. Pine trees are abundant in the modern boreal forest, which stretches across the north of Canada. Pine pollen is one of the most common types found in most Holocene pollen records from Canada. This grain is about 80 µm across. (Photo: Dr. David M. Jarzen, Canadian Museum of Nature, Ottawa).
2. A pollen grain from fireweed (Epilobium angustifolium), the floral emblem of the Yukon. This plant is pollinated by insects. Thus the grain is relatively large and sticky, often forming clumps of several grains, so that it attaches to insects as they visit the flower. Fireweed is a common plant in Canada. It has bright pink flowers and often grows on disturbed or burned-over areas, forming a vivid splash of colour. This grain is about 40 µm across. (Photo: Dr. David M. Jarzen, Canadian Museum of Nature, Ottawa).
3. A pre-Quaternary palynomorph, Aquilapollenites, from the Cretaceous Judith River Group. This palynomorph occurs in sediments from 74 to 76 million years ago. Rocks of the Judith River Group consist largely of mudstones and sandstones laid down by ancient rivers. They outcrop in the major river valleys, such as the Red Deer, Bow, Oldman and Milk River valleys, of southern Alberta. This grain is about 50 µm in length. (Photo: Dr. Dennis Braman, Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta).
4. Coring through the winter ice at Wizard Lake, Alberta. The team is working with a hand-operated piston corer. It is lowered to the lake bed through a hole cut in the ice. The piston is driven into the sediments and then the whole assembly is raised and the core of sediment is retrieved from the barrel. Using this relatively simple apparatus, it is possible, depending on sediment type, to obtain cores up to about 8 m depth in the sediments. (Photo: provided by A. B. Beaudoin, Provincial Museum of Alberta collection)
5. The biological microscope set up for pollen counting in the laboratory. Notice the radio - a vital piece of laboratory equipment! (Photo: provided by A. B. Beaudoin, Provincial Museum of Alberta collection)
The paper was written in 1996 and reflects the state of knowledge at that time. Some information (e.g., length of the Quaternary) has changed in recent years, but the text has not been altered. The essay was hosted on the Careers in Earth Sciences's website at the University of Waterloo, and was re-configured for its current location after that site closed. Latest update: April 10 2011