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QuickLinks

Amino Acid Racemization
Cation Ratio Dating
Corals
Cosmic Ray Exposure Dating
Dendrochronology
Electron Spin Resonance
Fission Track Dating
Fluorine Dating
Ice Core Dating
Luminescence Dating Methods
Obsidian Hydration Dating
Oxidizable Carbon Ratio Dating
Paleomagnetism Dating
Patination Dating
Pollen Dating
Radiocarbon Dating
Radiometric Dating Methods
Stratigraphy
Superposition

Chronological Dating: An Overview

Welcome to the Chronological Dating links page. These links are provided as additional information to go along with the topics covered on my website. At the time of this posting, the links are all in working order, but if you come across one that doesn't work, please contact me at WWDD.

Is Scientific Dating Really Important?

Many times in the field, a geologist or a paleontologist will happen upon something that will need to have an age determined. This can be a fossil, an outcrop, or a formation. There are a variety of ways to determine just how old that something is, and the age given to it can help in the understanding of what it represents to the scientist.

Dating is not necessary to demonstrate that evolution is a fact, however. Chronological sequence is all that is really required. However, human beings love to see factual precision, and we want to know how old something is.

Please remember that all dating methods, even those termed "absolute," are subject to margins of error. We say the Earth is 4.56 ± 0.02 billion years old. That is a very small amount of possible error range. There are 20 methods shown here. Modern studies almost always use two or more methods to confirm dating work and to build confidence in the results obtained.

Overviews of Dating

Content for Chronological Methods

Content for Chronological Methods by George H. Michaels and Brian M. Fagan, University of California. Includes an Introduction to Chronological Methods.

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Dating the Past

This is an excellent overview of dating methodologies, and is a chapter in a textbook on Archaeology. You may find it useful for the clear definitions, and for excellent links on a variety of topic. Many of these links also appear where appropriate below.

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eMuseum Dating Exhibit

Provides clear definitions of and explanations about many dating processes listed below. Also goes to some pains to mention problems encoutered with some of the methods.

Amino Acid Racemization

Amino Acid Geochronology

This is a relative, and sometimes absolute, dating method that relates the diagenesis of fossil protein preserved in carbonate materials with time (geologic age of the sample) and temperature (long term chemical temperature of the enclosing sediment). Stratigraphic applications of the method have been demonstrated from both marine and non-marine sequences all over the world using a variety of carbonate fossil materials including mollusks, foraminifera, bone, ostrich egg shells, ostracodes, and tooth enamel. A brief explanation is given at Bear Lake Methods: Amino Acid Dating.

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eMuseum -- Amino Acid Racemization

Provides a frank discussion of possible problems encountered when using this method, and the need for cross-checking results against other methods.

Cation Ratio Dating

eMuseum -- Cation Ratio Dating

Rocks are covered by a kind of varnish, a chemically-changed layer that builds up over time due to calcium and potassium seeping out of the rock. The cation ratio is determined by scraping the varnish from the carved or petroglyph surface back to the original rock surface and making a comparison of the two using a positively charged ion.

Corals

Coral Slide Set from NOAA

Corals exhibit seasonal growth bands very much like those in trees. Sometimes these bands are visible to the naked eye; usually, however, they are more visible in an x-ray. When paleoclimatologists drill a coral core, they can count the growth bands and date samples exactly. Long cores can cover several hundred years; this portion of a core from Urvina Bay in the Galápagos Islands covers the period from 1716 to 1735 A. D.

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Tidal Slowdown, Coral Growth, and the Age of the Earth

In certain modern corals we find growth-bands that indicate yearly, monthly, and even daily growth. There are about thirty daily bands per month and about 365 daily bands per year for modern corals and shellfish. But careful analysis of the growth-bands of fossil corals and shellfish from the Devonian and Pennsylvanian has confirmed that years in these periods contained more days than years do now (about 400).

Cosmic Ray Exposure Dating

Cosmic-ray Exposure Dating

This dating method relies on measuring certain isotopes produced by cosmic ray impacts on exposed rock surfaces. Because cosmic rays constantly bombard meteorites flying through space, this method has long been used to date the "flight time" of meteorites--that is the time from when they were chipped off a larger body (like an asteroid) to the time they land on Earth.

Dendrochronology

Bristlecone Pine Dendrochronology

Earth's oldest living inhabitant "Methuselah" at 4,767 years, has lived more than a millennium longer than any other tree. [ While this may be true, a shrub in Tasmania could be 40,000 years old. See Oldest Living Organism.]

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Dendrochronology -- Tree Rings

Tree-Ring dating is based on the principle that the growth rings on certain species of trees reflect variations in seasonal and annual rainfall. Trees from the same species, growing in the same area or environment will be exposed to the same conditions, and hence their growth rings will match at the point where their lifecycles overlap.

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The Principles of Dendochronology

The Principles of Dendochronology as compiled by Henri Grissino-Mayer of the Laboratory of Tree-Ring Research at the University of Arizona, Tucson.

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The Ultimate Tree-ring Pages

This really must be the ultimate web resource for this topic. You will find information about tree-rings, current research, and examples of practical applications of this science.

Electron Spin Resonance

Electron Spin Resonance

Also called electron paramagnetic resonance, ESR dating also relies on the changes in electron orbits and spins caused by radioactivity over time. However, ESR dating can be used over longer time periods, up to two million years, and works best on carbonates, such as in coral reefs and cave deposits. It has also seen extensive use in dating tooth enamel.

Fission Track Dating

eMuseum -- Fission-track Dating

Fission-track dating is one type of radioactive dating method used by archaeologists to determine the thermal age of artifacts containing uranium-bearing minerals. Fission tracks are created at a constant rate throughout time so that from the number of tracks present it is possible to determine the amount of time that has past since the track accumulation began. Dates from anywhere between twenty to one thousand million years ago can be determined with this particular technique.

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Fission Track Dating Warning: This is a PDF File!

Fission track dating is based on the microscopic observation and counting of etchable tracks left by the spontaneous fission of uranium in minerals. Since its development in 1963 the method attracted a steadily growing interest from geologists and geochronologists throughout the world. Apart from its relative experimental ease the success must be mainly ascribed to the specific ability of the method of unravelling the thermal and tectonic history of rocks, a potential which only became fully exploited during the last decade with the systematic introduction of track size analysis.

Fluorine Dating

eMuseum -- Flourine Dating

Fluorine dating is chiefly of value in determining whether bone implements or human skeletal remains found in association with other bones were buried at the same time. It was fluorine dating that was instrumental in the debunking of Piltdown Man.

Ice Core Dating

Ice Core Dating

There are four major ways of obtaining dates by using ice cores, and this page on the TalkOrigins site gives an overview of them.

Luminescence Dating Methods

Includes:

• Thermoluminescence (TL, stimulated by heat)
• Optical stimulated luminescence (OSL, stimulated by visible light)
• Infrared stimulated luminescence (IRSL, stimulated by infrared light)
• Radioluminescence (RL, stimulated by ionizing radiation)

Luminescence Dating -- Thermo/Optical

Scientists in North America first developed thermoluminescence dating of rock minerals in the 1950s and 1960s, and the University of Oxford, England first developed the thermoluminescence dating of fired ceramics in the 1960s and 1970s.During the 1970s and 1980s scientists at Simon Frasier University, Canada, developed standard thermoluminescence dating procedures used to date sediments. In 1985, they also developed optically stimulated luminescence dating techniques, which use laser light, to date sediments.

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Optically Stimulated Luminescence Dating (OSL)

Optically Stimulated Luminescence (OSL) dating is a relatively new alternative approach to chronological problems. Both quartz and feldspar rich sediments, which are otherwise undateable by conventional radiocarbon methods, can be absolutely dated (± ~10%) within a range of 100 to 200,000 years.

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Thermoluminescence

It can be applied to date a large variety of volcanic materials such as rhyolitic lava flows, tephras and other pyroclastic deposits. It can also date meteorite impact craters, earthquake-generated fault gouge material, contact heating and metamorphism of sediments baked by lava overflows, and anthropogenically heated materials such as ceramics, cooking hearths,and deliberately fire-treated rocks such as flints used by prehistoric people for toolmaking. Also see Quaternary TL Surveys - A Guide to Thermoluminescence Date Measurement. Additional information is available at Luminescence Dating.

Obsidian Hydration Dating

eMuseum -- Obsidian Hydration Dating

The actual measurement of hydration involves using light transmission to determine the amount of hydration, and therefore the relative age of the sample. Prepared slides are observed through a microscope to determine the amount of light transmission. White light and/or polarized light may be used in the analysis.

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Obsidian Hydration Dating

Obsidian, or volcanic glass, is formed by the rapid cooling of silica-rich lava. Although its precise chemical composition varies from one outcrop to another, it always contains >70% silica by weight. Humans often used obsidian as a raw material when making chipped stone tools.

Oxidizable Carbon Ratio Dating

eMuseum -- Oxidizable Carbon Ratio

Even though OCR has the potential to provide archaeologists and geologists with a method of finding accurate and precise age estimates from organic carbon within soil, it is still new and in the experimental stage. Scientists question both the methods of the procedure and the accuracy of the results, which is common and needed when any new scientific theory arises. Federal and State organizations, museums, Cultural Resource Management companies, archaeologists, pedologists, and geomorphologists are all currently conducting field studies for OCR dating at hundreds of sites in Northeastern North America and in parts of Europe.

Paleomagnetism Dating

Paleomagnetic and Archaeomagnetic Dating

After World War II, geologists developed the paleomagnetic dating technique to measure the movements of the magnetic north pole over geologic time. In the early to mid 1960s, Dr. Robert Dubois introduced this new absolute dating technique to archaeology as archaeomagnetic dating.

Patination Dating

eMuseum -- Patination Dating

Although it is not an actual dating technique, patination is used when multiple artifacts of the same type are found in the same area and under the same conditions. The use of this technique is to determine the age of the artifacts, relative to the others, by comparing the thickness of the patina on them. There are many variables that have to be calculated, and this makes dating lithics from patina formations a relative dating technique.

Pollen Dating

eMuseum -- Pollen Analysis

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. Nice graphic of pollen history at this site.

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Stratigraphic Palynology

Palynology is the branch of science dealing with microscopic, decay-resistant remains of certain plants and animals. It has many applications including archaeological palynology, Quaternary palynology , and stratigraphic palynology.

Radiocarbon Dating

C14 Resources

For learning more about radiocarbon methods, laboratories and databases.

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eMuseum -- C14 Dating Exhibit

This is an excellent, easy to understand explanation of the process. The accuracy of radiocoarbon dating was tested on objects with dates that were already known through historical records such as parts of the dead sea scrolls and some wood from an Egyptian tomb. Based on the results of these tests the analysis showed that C14 agreed very closely with the historical information.

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Oxford Radiocarbon Accelerator Unit

About research in radiocarbon methodology. Includes many protocols for adjusting results to account for fluctuations in atmospheric C14.

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Radiocarbon: The C14 Method

There are over 130 radiocarbon dating laboratories around the world producing radiocarbon assays for the scientific community. The Carbon14 technique has been and continues to be applied and used in many, many different fields including hydrology, atmospheric science, oceanography, geology, palaeoclimatology, archaeology and biomedicine.

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Radiocarbon Dating

An excellent series of short movies take students through a course of explanation and demonstration of C14 methods.

Radiometric Dating Methods

Age of the Earth

Radiometric Dating from The Evolution Evidence Page. The most compelling argument for an age of the earth of 4.5 billion years are the large number of independent tests that have been used to confirm this date. These tests have been performed on what are thought to be the earth's oldest surviving rocks, meteorites, and moon rocks. These tests have consistently given the same ages for each of these objects. Examples of a number of consistent dates derived from different methods are given.

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Geologic Time: Radiometric Time Scale

More on the basics from the United States Geological Service. Discussed six isoptopes commonly used to date very ancient rocks.

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Isochron Radiometric Dating

Isochron methods avoid the problems which can potentially result during radiometric testing.

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New Electron Microprobe Determines Ages of Rocks

A team of University of Massachusetts geologists is exploring a new way to determine the ages of ancient rocks, and refining our understanding of the timing and rates of the geologic events that have shaped the planet. The new method offers greater efficiency, and access to a much more detailed geologic record than current dating methods.

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Radiometric Dating -- A Christian Perspective

Radiometric Dating -- A Christian Perspective by Dr. Roger C. Wiens, Los Alamos National Laboratory. Also discusses other dating methodologies. This article should be a "must read" for any person interested in factualy accurate information on dating methods.

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Radiometric Dating Film Clips

By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined. A series of movie clips walks you through the process.

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Reliability of Radiometric Dating

Similar to this webpage, it presents many links to articles about radiometric dating and the age of the earth, some of which I do not list here for want of space.

Stratigraphy

William "Strata" Smith, a civil engineer and surveyor, was well acquainted with areas in southern England where "limestone and shales are layered like slices of bread and butter." His hobby of collecting and cataloging fossil shells from these rocks led to the discovery that certain layers contained fossils unlike those in other layers. Using these key or index fossils as markers, Smith could identify a particular layer of rock wherever it was exposed. Because fossils actually record the slow but progressive development of life, scientists use them to identify rocks of the same age throughout the world. See more information about "Strata" Smith and his original geologic map of England. Click on the map to see a larger version.

Geologic Time: Index Fossils

Keyed to the relative time scale are examples of index fossils, the forms of life which existed during limited periods of geologic time and thus are used as guides to the age of the rocks in which they are preserved.

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Stratigraphy and Cross-Dating/Biostratigraphy

Stratigraphy is the study of strata, or layers. Specifically, stratigraphy refers to the application of the Law of Superposition to soil and geological strata containing archaeological materials in order to determine the relative ages of layers. Cross-dating is a technique used to take advantage of consistencies in stratigraphy between parts of a site or different sites, and objects or strata with a known relative chronology. A specialized form of cross-dating, using animal and plant fossils, is known as biostratigraphy.

Superposition

Geologic Time: Relative Time Scale

James Hutton and William Smith advanced the concept of geologic time and strengthened the belief in an ancient world. Hutton, a Scottish geologist, first proposed formally the fundamental principle used to classify rocks according to their relative ages. He concluded, after studying rocks at many outcrops, that each layer represented a specific interval of geologic time. Further, he proposed that wherever uncontorted layers were exposed, the bottom layer was deposited first and was, therefore, the oldest layer exposed; each succeeding layer, up to the topmost one, was progressively younger. The Major Divisions of Geologic Time are shown here, arranged in chronological order with the oldest division at the bottom, the youngest at the top.

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Superposition -- It's a Law

One of the most fundamental principles of geology is the Law of Superposition. The law states that strata that are younger will be deposited on top of strata that are older, given normal conditions of deposition. This law is the guiding principle of stratigraphy, or the study of geological or soil layers. Stratigraphy is still the single best method that geologists have for determining the relative ages of geological materials.