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.
Absolute dating
Radiometric Dating Film Clips: By comparing the proportion of K to Ar in a sample of volcanic rock, and knowing the decay rate of K, the date that the rock formed can be determined. A series of movie clips walks you through the process. Gives the simple principles of how the process works. More on the basics from the United States Geological Service. Discussed six isoptopes commonly used to date very ancient rocks.
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. Isochron methods avoid the problems which can potentially result during radiometric testing. These are very nice pages from www. Age of the Earth: The most compelling argument for an age of the earth of 4.
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. A short but clear explanation about radioactive isotopes commonly used for determining ages of rocks with graphics and putting numbers on the geologic time scale, extending it back before the occurance of abundant index fossils.
This is a relatively new method intended to to improve the precision of uranium and thorium istopy methods. It excludes contamination and weathering of travertines and makes possible more precise dating of thin deposits of secondary carbonates. No web-based resource for this method is available.
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. Obsidian hydration dating is based on the fact that a fresh surface is created on a piece of obsidian in the tool manufacturing, or flintknapping, process.
Obsidian contains about 0. When a piece of obsidian is fractured, atmospheric water is attracted to the surface and begins to diffuse into the glass.
This results in the formation of a water rich hydration rind that increases in depth with time. The hydration process continues until the fresh obsidian surface contains about 3. This is the saturation point. The thickness of the hydration rind can be identified in petrographic thin sections cut normal to the surface and observed under a microscope.
A distinct diffusion front can be recognized by an abrupt change in refractive index at the inner edge of the hydration rind. These fronts or rinds of hydration are more dense than the unhydrated inside, and the unhydrated zone has different optical properties. Friedman and Smith reasoned that the degree of hydration observed on an obsidian artifact could tell archaeologists how long it had been since that surface was created by a flintknapper.
Introduction to Obsidian Hydration Dating: When a new surface of obsidian is exposed to the atmosphere, such as during the manufacture of glass tools, water begins to slowly diffuse from the surface into the interior of the specimen. When this hydrated layer or rind reaches a thickness of about 0.
Hydration rims formed on artifacts can vary in width from less than one micron for items from the early historic period to nearly 30 microns for early sites in Africa. 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.
Additional information is available at Luminescence Dating. Scientists in North America first developed thermoluminescence dating of rock minerals in the s and s, and the University of Oxford, England first developed the thermoluminescence dating of fired ceramics in the s and s. During the s and s scientists at Simon Frasier University, Canada, developed standard thermoluminescence dating procedures used to date sediments. In , they also developed optically stimulated luminescence dating techniques, which use laser light, to date sediments.
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: Provides a frank discussion of possible problems encountered when using this method, and the need for cross-checking results against other methods. 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. A brief description of the method. Scientists think that they have counted ice layers accurately. And, they think that one layer almost always means one year.
Introduction
But are they right? Varves form two or more distinctive layers at different seasons of the year. Gives a nice description about overcoming problems in the use of this method. Counting Sediment Layers in Rock: The basic reason for varves is that rivers run faster in the spring. A flooding river carries coarse material.
During the rest of the year, the river is slower, and carries finer material. The North American Varve Project: Tufts University website describing the research being done in establishing a North American varve chronology. Pollen analysis, study of vegetation history using the microfossils pollen grain and spores of size 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 million years ago can be found today.
Fossils and Their Place in Time and Nature
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. Pollen analysis is a method for reconstructing the past vegetation history in a particular area or context. As we know that vegetation cover in particular areas has altered over time, the technique used to be used as a generalized dating method.
However the development of more precise dating methods, such as radiocarbon-dating and dendrochronology, has meant that that aspect of pollen analysis has faded away. 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. 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 like the one shown at right.
When paleoclimatologists drill a coral core, they can count the growth bands and date samples exactly. 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 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 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.
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This technique is based on the principle that all objects absorb radiation from the environment. This process frees electrons within minerals that remain caught within the item.
Dating | geochronology | pcppk.com
Heating an item to degrees Celsius or higher releases the trapped electrons , producing light. This light can be measured to determine the last time the item was heated. Radiation levels do not remain constant over time. Fluctuating levels can skew results — for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item. Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.
It cannot be used to accurately date a site on its own. However, it can be used to confirm the antiquity of an item. Optically stimulated luminescence OSL dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to sunlight 'zeros' the luminescence signal.