Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Select the first letter of the word you are seeking from the list above
to jump to the appropriate section of the glossary or scroll down to it

  Return to Last Page     Return to Menu  

- A -

accelerator mass spectrometer   click this icon to hear the preceding term pronounced   (AMS)
a research instrument primarily used in physics to accelerate streams of charged subnuclear particles to high velocities in order to sort and analyze them.  This technique is now also used to count carbon isotope atoms for radiocarbon dating.  The advantage of this technique over the conventional radiocarbon method is that it requires a far smaller sample size and can potentially provide dates going back to around 100,000 B.P.  At present, however, AMS dates generally are for events less than 60,000 years old.
alpha particles   click this icon to hear the preceding term pronounced
positively charged subnuclear particles (consisting of 2 protons and 2 neutrons) given off by some isotopes when they decay or fission.
amino acids   click this icon to hear the preceding term pronounced
organic molecules that are building blocks of proteins.  There are at least 20 different kinds of amino acids in living things.  Proteins are composed of different combinations of amino acids assembled in chain-like molecules.  Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.
amino acid racemization click this icon to hear the preceding term pronounced dating
a method for dating organic matter that is based on the fact that amino acids progressively change to mirror image forms following the death of an organism--i.e., from L-amino acid to D-amino acid forms.  Aspartic acid in organic samples is commonly used for this dating technique.  Amino acid racemization could be considered to be a chronometric or a calibrated relative dating method.
anaerobic   click this icon to hear the preceding term pronounced
without oxygen.
angle of declination   click this icon to hear the preceding term pronounced
the degree difference between the direction of magnetic north and rotational north at a particular location.
archaeology   click this icon to hear the preceding term pronounced
the study of the prehistory or early history of societies and their cultures.  Unlike paleoanthropology, the focus of archaeology is mainly on the material remains of culture rather than biological evolution.
archaeomagnetic click this icon to hear the preceding term pronounced dating
See paleomagnetic dating.
argon-40/argon-39 click this icon to hear the preceding term pronounced dating   (40Ar/39Ar)
a radiometric dating method based on the changing ratio of argon-40 to argon-39  with the passage of time in volcanic rock or ash.  This technique was derived from potassium-argon datingThe argon-40/argon-39 method is usually more accurate than potassium-argon dating and doesn't require as large a sample.
artifacts   click this icon to hear the preceding term pronounced
things that are intentionally made according to a cultural pattern or inadvertently modified as a result of culturally patterned behavior.  Artifacts are usually relatively portable objects such as projectile points, ceramic pots, and baskets.
artifact time marker
an artifact type that was made by a particular culture during a limited time period.  When discovered clearly in association with ancient humans in an archaeological site, they are an indication of at least the relative time of the occupation.  When the independent dating of the artifact types is reliable, this can be considered a calibrated relative dating method.

Old World artifact types
used as time markers

  drawings of Old World paleolithic stone and bone artifact types used as time markers
atomic mass
the mass number of one atom of an isotope (e.g., carbon-14).  It is the sum of the masses of the protons, neutrons, and electrons of one atom.  See atomic number.
atomic number
the number of protons in the nucleus of one atom of an element.  See atomic mass.
Back to Top

- B -

beta particles   click this icon to hear the preceding term pronounced
energy charged subnuclear particles (consisting of an electron or a positron) given off by some isotopes when they decay or fission.
biostratigraphy   click this icon to hear the preceding term pronounced
the relative dating of early human sites by association with index fossils uncovered in the same strata as human evidence.  The assumption is that both the people and the species that is now an index fossil must have lived at about the same time.
B.P. date
a chronometric date that is measured in years before the present.  By convention, scientists have assigned 1950 A.D. in the Gregorian calendar as the present.
Back to Top

- C -

calibrated relative dating
use of a relative dating method that measures somewhat irregular occurring natural phenomena that have been cross-dated with at least one chronometric technique so that the dates are somewhat comparable from sites in one region to another.  Calibrated relative methods could be considered to be somewhere between ordinary relative methods and radiometric methods in terms of their ability to produce dates that closely approximate the actual date of a sample.  Amino acid racemization and paleomagnetic dating are generally considered to be either chronometric or calibrated relative methods. 
carbon-14 dating   (C-14)
see radiocarbon dating.
chronometric click this icon to hear the preceding term pronounced date
a date that places an event in its chronological position with reference to a universal time scale such as a calendar.   Such dates usually are given in terms of the number of years before or after a calendar starting point.  For instance, 1950 B.C. was 1950 years before the beginning date of the Gregorian calendar, which is commonly used today.  Chronometric dating methods include the use of written records, dendrochronology, and radiometric methods.  See relative date.
contemporary   click this icon to hear the preceding term pronounced
living or happening at the same time.
cosmic radiation   click this icon to hear the preceding term pronounced
streams of highly penetrating charged particles (composed of free electrons, protons, alpha particles, and a few heavier atom nuclei) that bombard the earth at high speed from outer space.  On entering our  upper atmosphere, they commonly collide with gas atoms and alter the atomic structures of those atoms.
crystal lattice   click this icon to hear the preceding term pronounced
the three-dimensional pattern of a crystalline solid.  There are characteristic lattice patterns identified for different minerals.
Back to Top

- D -

dendrochronology   click this icon to hear the preceding term pronounced
the study of annual growth-rings of trees, usually for the purpose of chronometric dating logs found in association with relatively recent archaeological sites.  Tree-ring sequences also are used as records of cycles in local climates.
DNA   click this icon to hear the preceding term pronounced    (deoxyribonucleic acid click this icon to hear the preceding term pronounced)
a large organic molecule that stores the genetic code for the synthesis of proteins.  Each chromosome consists mostly of a DNA molecule.  DNA is composed of sugars, phosphates and bases arranged in a double helix shaped molecular structure.  Segments of DNA correspond to specific genes.
Back to Top

- E -

electron spin resonance click this icon to hear the preceding term pronounced dating    (ESR)
a radiometric dating method based on the fact that background radiation causes electrons to separate from their atoms and become trapped in the crystal lattice of minerals When odd numbers of electrons are separated, there is a measurable change in the magnetic field (or spin) of the atoms.  Since the magnetic field progressively changes with time in a predictable way as a result of this process, it provides an atomic clock, or calendar, that can be used for dating purposes.  This technique is employed primarily to chronometrically date calcium carbonate in limestone, coral, teeth, mollusks, and egg shells.  It can also date quartz and flint.
Back to Top

- F -

fission track click this icon to hear the preceding term pronounced dating
a radiometric dating method based on the fact that when trace amounts of uranium-238 fission there is a release of highly energy-charged alpha particles which burn narrow fission tracks, or damage trails, through glassy materials such as obsidian (i.e., volcanic glass), mica, and zircon crystals.  The number of fission tracks is directly proportional to the time since the material cooled from a molten state.  The rate at which fission tracks occur is related to the half-life of uranium-238, which is approximately 4.5 billion years.
flint   click this icon to hear the preceding term pronounced
a kind of hard, rock with a glassy opaque appearance.  It was a favorite raw material for many prehistoric humans for the manufacture of tools such as knives and scraping implements.
fluorine click this icon to hear the preceding term pronounced analysis dating
a relative dating method based on the fact that bones buried in the ground progressively lose nitrogen and gain fluorine and other trace elements.  The rate at which these changes occur depends on the local environment.  If two bones from the same site have markedly different amounts of nitrogen and fluorine, it is a strong indication that they did not come from the same time period.  The bone with the least amount of nitrogen and the greatest amount of fluorine is most likely the oldest.
fossil   click this icon to hear the preceding term pronounced
any remains or traces of ancient organisms.  Often fossils are mineralized bone, though they have also been found in the form of casts, molds, animal tracks, frozen or desiccated bodies, and creatures trapped in amber.
Back to Top

- G -

geochronology   click this icon to hear the preceding term pronounced
a relative dating method based on the association of early human sites with changing features of the land, such as the advance and retreat of glaciers or the rise and fall of sea levels.  When these events are well dated, geochronology could be considered a reliable calibrated relative dating technique.  Associated evidence may be changes in the frequency of plant species measured by pollen count and other kinds of paleoecology evidence.
geological unconformities   click this icon to hear the preceding term pronounced
breaks in the original stratigraphic sequence of a geological deposit.   Understanding all of the unconformities in an area is a prerequisite for using stratigraphy for relative dating purposes.
geomagnetic polarity time scale   click this icon to hear the preceding term pronounced   (GPTS)
See paleomagnetic dating.
geomagnetic reversal time scale   click this icon to hear the preceding term pronounced   (GRTS)
See paleomagnetic dating.
Gregorian click this icon to hear the preceding term pronounced calendar
the most commonly used calendar system in the world today.  It is based on the older Julian calendar of the late Roman Empire but more accurately corresponds to the solar year of 365.2422 days.  The Julian calendar year is 365.25 days.  This is inaccurate by approximately 11 minutes a year.  The result is that the Julian calendar is out of sync by one day every 131 years.  The Gregorian calendar fixed this problem by changing the rules for leap years.  In the Julian system, a day is added to the end of February every 4 years.  In the Gregorian system a year is a leap year if it is divisible by 4 unless it is divisible by 100 but not by 400.  This eliminates leap years periodically in order to keep the calendar more synchronized with the solar year.  The Gregorian calendar was named after Pope Gregory XIII who officially approved it in 1582 A.D.  England and its colonies did not adopt it until 1752.
Back to Top

- H -

  graph of atomic decay showing a geometric rate of declining number of radioactive atoms in a sample
   Geometric rate of atomic decay
half-life
the amount of time for half of the atoms of a radioactive element in a sample to decay, or fission.  The reduction in the number of atoms follows a geometric scale--at the end of 2 half-lives, there are 1/4 of the atoms left; at the end of 3 half-lives, there are 1/8 remaining; etc.
hominin   click this icon to hear the preceding term pronounced
a species of the family Hominidae and tribe Hominini.  Humans are the only hominins today, however, there were others in the past 4-5 million years.
Back to Top

- I -

index fossil
remains of a plant or animal of a species that is known to have lived only during a specific time period.  The discovery of such a fossil in an archaeological site is circumstantial evidence of the approximate time period that it was occupied.  Fossil bones of horse and elephant related species are often used to relatively date fossils of our ancestors.  Index fossils are used for biostratigraphy.
isotopes   click this icon to hear the preceding term pronounced
any of two or more forms of an element that differ in terms of atomic mass but have the same atomic number--for example, carbon-12, carbon-13, and carbon-14 are all isotopes of carbon.
Back to Top

- J -

Back to Top

- K - 

Back to Top

- L -

locomotor patterns   click this icon to hear the preceding term pronounced
the methods an animal uses to move.  These may include such things as swimming, jumping, walking, etc.
Back to Top

- M -

minerals   click this icon to hear the preceding term pronounced
inorganic, naturally occurring materials consisting of specific elements.  They are usually rocks with a characteristic crystalline structure and other identifiable physical traits.  Quartz, talc, and ordinary table salt are examples of minerals.
morphology   click this icon to hear the preceding term pronounced
the physical form or structure of an organism or another object.   Species are usually identified from the fossil record based on morphological traits.
Back to Top

- N -

Back to Top

- O -

obsidian hydration click this icon to hear the preceding term pronounced dating
potentially, a chronometric dating method based on the fact that obsidian, or volcanic glass, progressively develops a thin chemically altered outer layer due to the absorption of water.  The thickness of this hydration layer is directly proportional to the amount of time since the rock was formed or since a fresh surface was exposed to the elements.  Since the rate of hydration varies between samples from different volcanic sources, this technique could arguably be considered relative rather than chronometric.
optically stimulated luminescence (OSL) dating
a comparatively new radiometric dating technique similar to thermal luminescence.  OSL is based on the fact that minerals in sediment grains are affected by prolonged exposure to light.  Specifically, light causes electrons of the mineral atoms to be progressively dislodged.  This provides a natural clock.  So far, the OSL technique has been used to date silty or sandy water deposited sediments that are 1/2 million years old or younger.
oxidizable carbon ratio (OCR) dating
an experimental dating technique based on the fact that organic carbon in soil humus and charcoal progressively convert to oxidizable carbon over time.  The ratios of these two forms of carbon vary directly with the age of the material.  This technique requires an inexpensive chemical analysis procedure.  The effective time range for OCR dating has not yet been established.
Back to Top

- P -

paleoanthropology   click this icon to hear the preceding term pronounced
the study of the fossil and archaeological record of humans and their primate ancestors.  It is also known as human paleontology.
paleoecology   click this icon to hear the preceding term pronounced
the study of ancient environments.  See geochronology and palynology.
paleomagnetic click this icon to hear the preceding term pronounced dating
dating methods based on the fact that the magnetic north pole wanders around the rotational north pole and has repeatedly reversed position with the magnetic south pole at irregular intervals in the past.  There are permanent records of these movements in the form of thermoremnant magnetism found in burned clay and rock as well as geological deposits of volcanic origin Archaeomagnetic dating is the term generally used for dating based on the wandering of the magnetic north pole around the rotational north pole over the last 10,000 years or so.  Geomagnetic reversal time scale click this icon to hear the preceding term pronounced (GRTS) dating and geomagnetic polarity time scale click this icon to hear the preceding term pronounced (GPTS) dating are terms applied to the method based on the much longer term reversals of the magnetic poles.  The two related paleomagnetic dating methods have been considered by some researchers to be chronometric and calibrated relative by others.
paleontology   click this icon to hear the preceding term pronounced
the study of earlier forms of life present in the fossil record.   See paleoanthropology.
paleospecies    click this icon to hear the preceding term pronounced
a group of similar fossils considered to be members of the same species because the range of their morphological variation does not exceed the range of variation of a living species.  See species.
palynology    click this icon to hear the preceding term pronounced
the study of plant pollen, usually for the purpose of reconstructing ancient climates and dating soil strata.  Palynology is an important tool of paleoecology.
pathology    click this icon to hear the preceding term pronounced
the study of conditions, processes, or results of diseases.  Pathology also is used to refer to any abnormal physiological condition.
permafrost    click this icon to hear the preceding term pronounced
permanently frozen soil.  This is a common condition above the Arctic Circle and in other similarly cold environments.
photosynthesis    click this icon to hear the preceding term pronounced
the process by which plants, algae, and some bacteria use energy from sunlight to create new organic molecules out of carbon dioxide, water, and various nutrients.
pollen   click this icon to hear the preceding term pronounced
the male sex spores of flowering plants.  Pollen particles are usually nearly invisible, except in large concentrations, due to their extremely small size.  They can survive for hundreds of thousands of years in silty, anaerobic soils, such as mud sediments at the bottom of a lake.  When excavated from early human sites, they can be used to reconstruct what the climate was like at the time of the occupations as well as relatively date them.
populational click this icon to hear the preceding term pronounced viewpoint
the idea that if two fossils have major similarities they should be categorized as being members of the same species.  From this perspective, minor anatomical differences within the same population are expected since the members of living species have individual variation.  People who advocate this viewpoint are also referred to in the biological sciences as "lumpers".  See typological viewpoint.
potassium-argon click this icon to hear the preceding term pronounced dating    (K-Ar)
a radiometric dating method based on the fact that potassium-40 in volcanic rock decays into argon-40 and calcium-40 at a known rate.  The half-life of potassium-40 is approximately 1.3 billion years.  Chronometric dates are determined by measuring the amount of argon-40 in a sample.  Similarly, argon-40 and argon-39 ratios can be used for chronometric dating.
primary context
referring to the position in a site where an object was originally deposited.  Finding an artifact or fossil in primary context allows a researcher to apply the principle of association in dating and interpreting it.  This cannot be done if the object is in a secondary context, which is to say that it was moved to a new location after the original deposition.
principle of association
the assumption that if two objects are found in their primary context in the same strata of a site, they very likely date to the same time period.
principle of superposition   click this icon to hear the preceding term pronounced
the assumption that if there are layers in a sedimentary deposit, those laid down first will be on the bottom and those laid down last will be on the top.  This is the basis of using stratigraphy as a relative dating method.
proteins   click this icon to hear the preceding term pronounced
any of a large number of complex organic molecules that are composed of one or more chains of amino acids.  Proteins can serve a wide variety of functions through their ability to bind to other molecules.  Proteins may be enzymes, hormones, antibodies, structural components, or gas-transporting molecules.
Back to Top

- Q -

Back to Top

- R -

racemization
the process by which amino acids change from the L-molecule form to their mirror image D-molecule form.  This occurs naturally following the death of cells.  See amino acid racemization dating.
radiocarbon click this icon to hear the preceding term pronounced dating    (C-14 pronounce word)
a radiometric dating method based on the fact that the amount of carbon-14 steadily decreases in all organisms after death.  The reduction in the frequency of this isotope in a sample occurs at a half-life of 5730 40 years.   This technique is used to provide chronometric dates for organic materials such as bone, shell, wood, and charcoal.
radiometric click this icon to hear the preceding term pronounced dating
referring to techniques for chronometric dating based on known half-lives of particular isotopes or the rate of other cumulative changes in atoms resulting from radioactivity.  Examples include electron spin resonance, fission track, potassium-argon, radiocarbon, and thermoluminescence dating.
relative date
a date that gives the time of an event only with reference to another event that is not worldwide in scale.  It only indicates that one event occurred earlier or later than another.  For instance, the observation that strata 2 is younger than strata 1 beneath it in a geological deposit does not provide information about how many years ago strata 2 was laid down.  It only indicates its age relative to strata 1.  In addition to the use of stratigraphy, relative dating methods include biostratigraphy and fluorine analysis dating.  See chronometric date.
rotational north pole
the point on the northern extremity of the earth where the axis of rotation is located.  Compared to the magnetic north pole, the rotational one is relatively stable.
Back to Top

- S -

  seriation graph of the frequency of three pottery styles changing through time
seriation    click this icon to hear the preceding term pronounced
a relative dating method based on the fact that artifact types change through time in frequency as a result of new technologies, styles, and available construction materials.  The frequency of artifact types in a stratum can be compared to known frequency changes previously recorded for an ancient culture.  In this way, the stratum can be dated relative to other strata or sites.  When a seriation sequence has been cross-calibrated with reliable chronometric dating methods, it can be considered a calibrated relative technique.
species
the largest natural population of organisms that can potentially interbreed to produce fertile offspring.  It is commonly assumed that members of one species are reproductively isolated from members of all other species (i.e., they cannot mate with them to produce fertile offspring).  However, we must be cautious in defining species with this criterion because members of very closely related species can sometimes produce offspring together, and a small fraction of those may be fertile to some degree.  This is the case with mules, which are the product of mating between horses and donkeys.  About one out of 10,000 mules is fertile.  This suggests that some species differences are a matter of degree.  See paleospecies.
standard deviation
a statistical measure of the dispersion (or spread) from the arithmetic mean (or average) of a group of scores.  Chronometric dates derived with a radiometric method are published with a "plus or minus" factor, which usually is a range of dates within one standard deviation above and below the mean.  This should be read as a 67% likelihood that the actual date falls within the given range.
stratigraphy   click this icon to hear the preceding term pronounced
the study of geological strata, or layers of rock or soil, usually for relative dating based on the principle of superposition.
suture click this icon to hear the preceding term pronounced joint
the irregular line of joining between two bones, especially between the bone plates of the skull in vertebrates.
Back to Top

- T -

taphonomy   click this icon to hear the preceding term pronounced
the study of the conditions under which plants, animals, and other organisms become altered after death, buried, and sometimes preserved as fossils.
taxonomy   click this icon to hear the preceding term pronounced
naming, describing, and classifying organisms into different categories on the basis of their appearance and other diagnostic characteristics as well as their evolutionary relationships.  The biological sciences primarily use the Linnaean classification system for this purpose.
tectonic click this icon to hear the preceding term pronounced movement
lateral and/or vertical movement of segments of the earth's crust.  The continents and the ocean floors consist of tectonic plates that are moving relative to each other.  On average, such movements are about 1 inch per year.
thermoluminescence click this icon to hear the preceding term pronounced dating    (TL)
a radiometric dating  method based on the fact that trace amounts of radioactive atoms, such as uranium and thorium, in some kinds of rock, soil, and clay produce constant low amounts of background ionizing radiation.  The atoms of crystalline solids, such as pottery and rock, can be altered by this radiation.  Specifically, the electrons of quartz, feldspar, diamond, or calcite crystals can become displaced from their normal positions in atoms and trapped in imperfections in the crystal lattice of the rock or clay molecules.  These energy charged electrons progressively accumulate over time.  When a sample is heated to high temperatures in a laboratory, the trapped electrons are released and return to their normal positions in their atoms.  This causes them to give off their stored energy in the form of light impulses (photons).  This light is referred to as thermoluminescence (literally "heat light").  A similar effect can be brought about by stimulating the sample with infrared light.  The intensity of thermoluminescence is directly related to the amount of accumulated changes produced by background radiation, which, in turn, varies with the age of the sample and the amount of trace radioactive elements it contains.
thermoremnant magnetism    click this icon to hear the preceding term pronounced
magnetic fields that are altered or formed in atoms of iron by heat in excess of 1100 F. (600 C.).  Such fields line up with the magnetic field of the planet at the time of the exposure to a high temperature.  They will remain oriented to that direction indefinitely despite the fact that the true position of magnetic north wanders over thousands of miles around the rotational north pole and even reverses with the magnetic south pole over longer periods of time.   See paleomagnetic dating.
tree-ring dating
see dendrochronology.
typological click this icon to hear the preceding term pronounced viewpoint
the idea that if two fossils look slightly different, they must be categorized as being from two different species.  This approach emphasizes minor differences.  People who maintain this approach are generally referred to in the biological sciences as "splitters".  See populationist viewpoint.
Back to Top

- U -

universal time scale
a time scale, or calendar, that can be used any place in the world since it has a finite beginning point from which any earlier or later event can be related exactly.  All chronometric dates are given in terms of a universal time scale.
uranium series dating
a group of dating techniques based on measurement of the radioactivity of short-lived daughter isotopes of uranium.
uranium-thorium click this icon to hear the preceding term pronounced dating
a radiometric dating technique based on the rate at which uranium-238 and thorium-230 fission.  This method has been used to date organic marine sediments, bone, wood, coral, stone, and soil from deep water, cave, or land fall areas.  The time range that has been dated with this method so far is less than 300,000 to about 1,000,000 years ago.  The half-life of U-238 is 4.468 billion years and the half-life of Th-230 is 75,380 years.  This is one of several uranium series dating methods. 
Back to Top

- V -

varve click this icon to hear the preceding term pronounced analysis
a calibrated relative or potentially chronometric dating technique based on counting annual silt deposits (i.e., varves) in former lakes resulting from the summer melt of glaciers.  In Scandinavia, this geological clock has been used to date associated archaeological evidence from the melt years of the last ice age, which began its final retreat about 15,000 years ago.
Back to Top

- W -

Back to Top

- X -

Back to Top

- Y - 

Back to Top

- Z -

Back to Top

Copyright 1998-2013 by Dennis O'Neil. All rights reserved.
illustration credits