Radiometric DatingScience in Christian Perspective. Radiometric Dating. A Christian Perspective. Roger C. Wiens has a PhD in Physics, with a minor in Geology.
There are many different radioactive isotopes that are used for radiometric dating. For example, there is a radioactive form of potassium potassium that decays into argon argon The unstable potassium isotope is called the parent while the argon product is called the daughter.
There are a couple of different radioactive forms of uranium that decay into lead. There is a radioactive form of thorium that also decays into lead. There is an isotope of samarium that decays into neodymium, and one of rubidium that decays into strontium. Radioactive dating is often illustrated with an hour glass. The sand grains at the top of the sealed glass are like the atoms of the parent isotope in the rock, and those at the bottom like the atoms of the daughter. Radioactive decay is where the parent atoms change as a result of radioactive decay into daughter atoms, like the individual grains of sand falling from the top to the bottom of the glass.
The hourglass depends on the sand falling at a regular rate. Like an hour glass, it is said, you simply measure the parent and the daughter elements and you can calculate the age. However, an hour glass is only useful if we saw it turned over and observed that the bottom glass was empty. In other words, the hourglass only works when we know its initial condition. Unlike the hourglass, we do not know how much of each isotope was in the rock in the beginning. Neither can we travel into the past to make the necessary measurements.
All we can do is guess. This is the fatal problem that essentially makes radioactive dating useless as a primary method for determining age. Geologists prefer to make indirect assumptions.
They may assume that different minerals in the rock originally had the same isotopic ratios to start with. Or they may assume that different rock samples from the same geographical area had the same ratio. Each dating method uses different kinds of assumptions to get around this problem for radiometric dating—the deadly problem caused by the fact that we cannot make measurements in the past.
Apart from the fatal problem of not knowing the initial conditions, there is another problem that is just as deadly. An hour glass is only useful if it is not disturbed. But after rocks crystallize from molten magma, they can be heated and cooled; they can be affected by metamorphic events and groundwater. These geologic events can cause elements to be gained and lost to the rock.
How can we know what disturbances have affected the elements in our rocks? Again, we can only guess. Did you hear about the old wood cutter who was bragging about his axe? When a geologist hammers off a sample of rock he needs to know its history. Different minerals would have crystallized at different times depending on the way the molten magma cooled.
Some small pieces of other rock, or even some foreign minerals, may have been carried along by the magma and existed long before the rock crystallized.
Other minerals may have grown inside the rock much later, during a time when the area was heated and metamorphosed. Some minerals may have crystallized even later still when ground waters in the area percolated through the pores of the rock. No, the assumptions of AiG are not even based on anything observable. Quite the contrary, they are literally based on nothing.
And that was the point—even though pagan temples had physical idols, in reality those idols represented nothing that corresponded to reality in any way.
In a similar way, AiG actually prides itself…on nothing. Such is idolatry—the worship of an image that ultimately corresponds to nothing that is real. There is no other reliable way to measure age of rocks, only by using different types of radiometric dating for the different ranges of time periods. After halving 5 times, less than 3.
After halving 10 times, do the math for the powers of 2 in reverse, approximately. So there are reasonable limits for each radioactive isotope and its decay, whether U, K40, Th See the good intro description in Wikipedia for Radioactive Decay. The issue is that God never brings up this area of science in the Bible, probably because to Him it is not important.
Radiometric dating--the process of determining the age of rocks from the decay have sometimes been divisive for people who regard the Bible as God's word. Answer: Radiometric dating does not fit with the “young earth” view. Radiometric dating is a method which scientists use to determine the age of various. Read Radiometric Dating from Christian radio ministry Answers with Ken Ham God's word unmistakably teaches a young earth and universe (“the heavens”).
So Joel and other Christians who try to compare real science and the Bible are just showing what the Bible does not try to prove, although the young earth group has its own faith in their view of God and science beyond any reasonable rationale within science. Thanks for the well-written clarification on these points, Joel.
By the way, nice picture comparison of you and Hume. You do look like him. No, historical science very much is science. It works in exactly the same way as any other kind of science. Form a hypothesis; make some predictions based on it; design a test to see if those predictions are met; conduct test; confirm, improve, adjust or discard hypothesis as appropriate. One of the most useful tests is to cross-check the results of two studies whose assumptions are independent of each other.
If different results are in agreement the majority of the time, then we can safely assume that the results concerned are indeed correct. I guess we will never know unless they tell us.
The ratio of argon to argon in air is well known, at Thus, if one measures argon as well as argon, one can calculate and subtract off the air-argon to get an accurate age. One of the best ways of showing that an age-date is correct is to confirm it with one or more different dating. Although potassium-argon is one of the simplest dating methods, there are still some cases where it does not agree with other methods. When this does happen, it is usually because the gas within bubbles in the rock is from deep underground rather than from the air.
This gas can have a higher concentration of argon escaping from the melting of older rocks. This is called parentless argon because its parent potassium is not in the rock being dated, and is also not from the air. In these slightly unusual cases, the date given by the normal potassium-argon method is too old. However, scientists in the mids came up with a way around this problem, the argon-argon method, discussed in the next section.
Even though it has been around for nearly half a century, the argon-argon method is seldom discussed by groups critical of dating methods. This method uses exactly the same parent and daughter isotopes as the potassium-argon method.
In effect, it is a different way of telling time from the same clock. Instead of simply comparing the total potassium with the non-air argon in the rock, this method has a way of telling exactly what and how much argon is directly related to the potassium in the rock. In the argon-argon method the rock is placed near the center of a nuclear reactor for a period of hours. A nuclear reactor emits a very large number of neutrons, which are capable of changing a small amount of the potassium into argon Argon is not found in nature because it has only a year half-life.
This half-life doesn't affect the argon-argon dating method as long as the measurements are made within about five years of the neutron dose. The rock is then heated in a furnace to release both the argon and the argon representing the potassium for analysis. The heating is done at incrementally higher temperatures and at each step the ratio of argon to argon is measured. If the argon is from decay of potassium within the rock, it will come out at the same temperatures as the potassium-derived argon and in a constant proportion.
On the other hand, if there is some excess argon in the rock it will cause a different ratio of argon to argon for some or many of the heating steps, so the different heating steps will not agree with each other.
Figure 2 is an example of a good argon-argon date. The fact that this plot is flat shows that essentially all of the argon is from decay of potassium within the rock. The potassium content of the sample is found by multiplying the argon by a factor based on the neutron exposure in the reactor. When this is done, the plateau in the figure represents an age date based on the decay of potassium to argon There are occasions when the argon-argon dating method does not give an age even if there is sufficient potassium in the sample and the rock was old enough to date.
This most often occurs if the rock experienced a high temperature usually a thousand degrees Fahrenheit or more at some point since its formation. If that occurs, some of the argon gas moves around, and the analysis does not give a smooth plateau across the extraction temperature steps. An example of an argon-argon analysis that did not yield an age date is shown in Figure 3. Notice that there is no good plateau in this plot. In some instances there will actually be two plateaus, one representing the formation age, and another representing the time at which the heating episode occurred.
Is radiometric dating a reliable method for estimating the age of .. The earth may have had very little c in its atmosphere when God first. Radioactive dating may be one of the big questions looming in your mind. Note too that radioactive dating is something that most people don't .. The Bible declares: In the beginning God created the heavens and the earth. Radiometric Dating and 6, Years — Part One. Article#: Stress-shifting is a Bible teaching that is truly a life-transforming truth. Those believers who work.
But in most cases where the system has been disturbed, there simply is no date given. The important point to note is that, rather than giving wrong age dates, this method simply does not give a date if the system has been disturbed. This is also true of a number of other igneous rock dating methods, as we will describe below.
Figure 3. In nearly all of the dating methods, except potassium-argon and the associated argon-argon method, there is always some amount of the daughter product already in the rock when it cools. Using these methods is a little like trying to tell time from an hourglass that was turned over before all of the sand had fallen to the bottom.
One can think of ways to correct for this in an hourglass: One could make a mark on the outside of the glass where the sand level started from and then repeat the interval with a stopwatch in the other hand to calibrate it. Or if one is clever she or he could examine the hourglass' shape and determine what fraction of all the sand was at the top to start with. By knowing how long it takes all of the sand to fall, one could determine how long the time interval was.
Similarly, there are good ways to tell quite precisely how much of the daughter product was already in the rock when it cooled and hardened. Figure 4 is an important type of plot used in rubidium-strontium dating. Figure 5. This works because if there were no rubidium in the sample, the strontium composition would not change. The slope of the line is used to determine the age of the sample. As the rock starts to age, rubidium gets converted to strontium.
The amount of strontium added to each mineral is proportional to the amount of rubidium present. The solid line drawn through the samples will thus progressively rotate from the horizontal to steeper and steeper slopes. From that we can determine the original daughter strontium in each mineral, which is just what we need to know to determine the correct age. It also turns out that the slope of the line is proportional to the age of the rock. The older the rock, the steeper the line will be.
If the slope of the line is m and the half-life is hthe age t in years is given by the equation. For a system with a very long half-life like rubidium-strontium, the actual numerical value of the slope will always be quite small. To give an example for the above equation, if the slope of a line in a plot similar to Fig.
Several things can on rare occasions cause problems for the rubidium-strontium dating method. One possible source of problems is if a rock contains some minerals that are older than the main part of the rock. This can happen when magma inside the Earth picks up unmelted minerals from the surrounding rock as the magma moves through a magma chamber. Usually a good geologist can distinguish these "xenoliths" from the younger minerals around them. If he or she does happen to use them for dating the rock, the points represented by these minerals will lie off the line made by the rest of the points.
What is a Christian to make of radioactive dating? The problem is that the Bible plainly says that the world was created by God in six days.
Another difficulty can arise if a rock has undergone metamorphism, that is, if the rock got very hot, but not hot enough to completely re-melt the rock.
In these cases, the dates look confused, and do not lie along a line. Some of the minerals may have completely melted, while others did not melt at all, so some minerals try to give the igneous age while other minerals try to give the metamorphic age. In these cases there will not be a straight line, and no date is determined. In a few very rare instances the rubidium-strontium method has given straight lines that give wrong ages. This can happen when the rock being dated was formed from magma that was not well mixed, and which had two distinct batches of rubidium and strontium.
One magma batch had rubidium and strontium compositions near the upper end of a line such as in Fig. In this case, the. This is called a two-component mixing line. It is a very rare occurrence in these dating mechanisms, but at least thirty cases have been documented among the tens of thousands of rubidium-strontium dates made. The agreement of several dating methods is the best fail-safe way of dating rocks.
All of these methods work very similarly to the rubidium-strontium method. They all use three-isotope diagrams similar to Figure 4 to determine the age. The samarium-neodymium method is the most-often used of these three. It uses the decay of samarium to neodymium, which has a half-life of billion years. The ratio of the daughter isotope, neodymium, to another neodymium isotope, neodymium, is plotted against the ratio of the parent, samarium, to neodymium If different minerals from the same rock plot along a line, the slope is determined, and the age is given by the same equation as above.
The samarium-neodymium method may be preferred for rocks that have very little potassium and rubidium, for which the potassium-argon, argon-argon, and rubidium-strontium methods might be difficult. The samarium-neodymium method has also been shown to be more resistant to being disturbed or re-set by metamorphic heating events, so for some metamorphosed rocks the samarium-neodymium method is preferred. For a rock of the same age, the slope on the neodymium-samarium plots will be less than on a rubidium-strontium plot because the half-life is longer.
However, these isotope ratios are usually measured to extreme accuracy--several parts in ten thousand--so accurate dates can be obtained even for ages less than one fiftieth of a half-life, and with correspondingly small slopes. The lutetium-hafnium method uses the 38 billion year half-life of lutetium decaying to hafnium This dating system is similar in many ways to samarium-neodymium, as the elements tend to be concentrated in the same types of minerals.
Since samarium-neodymium dating is somewhat easier, the lutetium-hafnium method is used less often. The rhenium-osmium method takes advantage of the fact that the osmium concentration in most rocks and minerals is very low, so a small amount of the parent rhenium can produce a significant change in the osmium isotope ratio. The half-life for this radioactive decay is 42 billion years. The non-radiogenic stable isotopes, osmium orare used as the denominator in the ratios on the three-isotope plots.
This method has been useful for dating iron meteorites, and is now enjoying greater use for dating Earth rocks due to development of easier rhenium and osmium isotope measurement techniques.
Uranium-Lead and related techniques. The uranium-lead method is the longest-used dating method. It was first used inabout a century ago. The uranium-lead system is more complicated than other parent-daughter systems; it is actually several dating methods put together.
Natural uranium consists primarily of two isotopes, U and U, and these isotopes decay with different half-lives to produce lead and lead, respectively. In addition, lead is produced by thorium Only one isotope of lead, lead, is not radiogenic. The uranium-lead system has an interesting complication: none of the lead isotopes is produced directly from the uranium and thorium. Each decays through a series of relatively short-lived radioactive elements that each decay to a lighter element, finally ending up at lead.
Since these half-lives are so short compared to U, U, and thorium, they generally do not affect the overall dating scheme. The result is that one can obtain three independent estimates of the age of a rock by measuring the lead isotopes and their parent isotopes.
Long-term dating based on the U, U, and thorium will be discussed briefly here; dating based on some of the shorter-lived intermediate isotopes is discussed later.
The uranium-lead system in its simpler forms, using U, U, and thorium, has proved to be less reliable than many of the other dating systems. This is because both uranium and lead are less easily retained in many of the minerals in which they are found. Yet the fact that there are three dating systems all in one allows scientists to easily determine whether the system has been disturbed or not.
Using slightly more complicated mathematics, different combinations of the lead isotopes and parent isotopes can be plotted in such a way as to. One of these techniques is called the lead-lead technique because it determines the ages from the lead isotopes alone. Some of these techniques allow scientists to chart at what points in time metamorphic heating events have occurred, which is also of significant interest to geologists. The Age of the Earth.
We now turn our attention to what the dating systems tell us about the age of the Earth. The most obvious constraint is the age of the oldest rocks. These have been dated at up to about four billion years.
But actually only a very small portion of the Earth 's rocks are that old. From satellite data and other measurements we know that the Earth's surface is constantly rearranging itself little by little as Earth quakes occur. Such rearranging cannot occur without some of the Earth's surface disappearing under other parts of the Earth's surface, re-melting some of the rock. So it appears that none of the rocks have survived from the creation of the Earth without undergoing remelting, metamorphism, or erosion, and all we can say--from this line of evidence--is that the Earth appears to be at least as old as the four billion year old rocks.
When scientists began systematically dating meteorites they learned a very interesting thing: nearly all of the meteorites had practically identical ages, at 4. These meteorites are chips off the asteroids. When the asteroids were formed in space, they cooled relatively quickly some of them may never have gotten very warmso all of their rocks were formed within a few million years.
The asteroids' rocks have not been remelted ever since, so the ages have generally not been disturbed. Meteorites that show evidence of being from the largest asteroids have slightly younger ages.
The moon is larger than the largest asteroid. Most of the rocks we have from the moon do not exceed 4. The samples thought to be the oldest are highly pulverized and difficult to date, though there are a few dates extending all the way to 4. Most scientists think that all the bodies in the solar system were created at about the same time. Evidence from the uranium, thorium, and lead isotopes links the Earth's age with that of the meteorites. This would make the Earth 4. Figure 6. There is another way to determine the age of the Earth.
If we see an hourglass whose sand has run out, we know that it was turned over longer ago than the time interval it measures. Similarly, if we find that a radioactive parent was once abundant but has since run out, we know that it too was set longer ago than the time interval it measures.
There are in fact many, many more parent isotopes than those listed in Table 1. However, most of them are no longer found naturally on Earth--they have run out. Their half-lives range down to times shorter than we can measure. Every single element has radioisotopes that no longer exist on Earth! Many people are familiar with a chart of the elements Fig. Nuclear chemists and geologists use a different kind of figure to show all of the isotopes. It is called a chart of the nuclides.
Figure 7 shows a portion of this chart. It is basically a plot of the number of protons vs. Recall that an element is defined by how many protons it has.
Each element can have a number of different isotopes, that is. Figure 7. A portion of the chart of the nuclides showing isotopes of argon and potassium, and some of the isotopes of chlorine and calcium. Isotopes shown in dark green are found in rocks. Isotopes shown in light green have short half-lives, and thus are no longer found in rocks. Short-lived isotopes can be made for nearly every element in the periodic table, but unless replenished by cosmic rays or other radioactive isotopes, they no longer exist in nature.
So each element occupies a single row, while different isotopes of that element lie in different columns.
For potassium found in nature, the total neutrons plus protons can add up to 39, 40, or Potassium and are stable, but potassium is unstable, giving us the dating methods discussed above. Besides the stable potassium isotopes and potassium, it is possible to produce a number of other potassium isotopes, but, as shown by the half-lives of these isotopes off to the side, they decay away.
Now, if we look at which radioisotopes still exist and which do not, we find a very interesting fact. Nearly all isotopes with half-lives shorter than half a billion years are no longer in existence. For example, although most rocks contain significant amounts of Calcium, the isotope Calcium half-lifeyears does not exist just as potassium, etc. Just about the only radioisotopes found naturally are those with very long half-lives of close to a billion years or longer, as illustrated in the time line in Fig.
The only isotopes present with shorter half-lives are those that have a source constantly replenishing them.
Chlorine shown in Fig. In a number of cases there is. Some of these isotopes and their half-lives are given in Table II. This is conclusive evidence that the solar system was created longer ago than the span of these half lives! On the other hand, the existence in nature of parent isotopes with half lives around a billion years and longer is strong evidence that the Earth was created not longer ago than several billion years.
The Earth is old enough that radioactive isotopes with half-lives less than half a billion years decayed away, but not so old that radioactive isotopes with longer half-lives are gone. This is just like finding hourglasses measuring a long time interval still going, while hourglasses measuring shorter intervals have run out. Cosmogenic Radionuclides: Carbon, Beryllium, Chlorine Extinct Isotope Half-Life.
Years Plutonium 82 million Iodine 16 million Palladium 6. Unlike the radioactive isotopes discussed above, these isotopes are constantly being replenished in small amounts in one of two ways. The bottom two entries, uranium and thorium, are replenished as the long-lived uranium atoms decay.
These will be discussed in the next section. The other three, Carbon, beryllium, and chlorine are produced by cosmic rays--high energy particles and photons in space--as they hit the Earth's upper atmosphere. Very small amounts of each of these isotopes are present in the air we breathe and the water we drink. As a result, living things, both plants and animals, ingest very small amounts of carbon, and lake and sea sediments take up small amounts of beryllium and chlorine The cosmogenic dating clocks work somewhat differently than the others.
Carbon in particular is used to date material such as bones, wood, cloth, paper, and other dead tissue from either plants or animals.
To a rough approximation, the ratio of carbon to the stable isotopes, carbon and carbon, is relatively constant in the atmosphere and living organisms, and has been well calibrated. Once a living thing dies, it no longer takes in carbon from food or air, and the amount of carbon starts to drop with time.
Since the half-life of carbon is less than 6, years, it can only be used for dating material less than about 45, years old. Dinosaur bones do not have carbon unless contaminatedas the dinosaurs became extinct over 60 million years ago. But some other animals that are now extinct, such as North American mammoths, can be dated by carbon Also, some materials from prehistoric times, as well as Biblical events, can be dated by carbon The carbon dates have been carefully cross-checked with non-radiometric age indicators.
For example growth rings in trees, if counted carefully, are a reliable way to determine the age of a tree.
Creation Radiometric Dating and the Age of the Earth
Each growth ring only collects carbon from the air and nutrients during the year it is made. To calibrate carbon, one can analyze carbon from the center several rings of a tree, and then count the rings inward from the living portion to determine the actual age.
The development of radiometric dating during the early decades of the 20th . and dying during the long geologic ages before God could get around to creating . When Genesis talks about “kinds,” those are God's own scientific . that the motivating factor scientists use radiometric dating isn't “to deny God. Does radiometric dating show that rocks are millions of years old? No! God's word unmistakably teaches a young earth and universe (“the.
This has been done for the "Methuselah of trees", the bristlecone pine trees, which grow very slowly and live up to 6, years. Scientists have extended this calibration even further.
These trees grow in a very dry region near the California-Nevada border.
God and radiometric dating
Dead trees in this dry climate take many thousands of years to decay. Growth ring patterns based on wet and dry years can be correlated between living and long dead trees, extending the continuous ring count back to 11, years ago. An effort is presently underway to bridge the gaps so as to have a reliable, continuous record significantly farther back in time. The study of tree rings and the ages they give is called "dendrochronology". Calibration of carbon back to almost 50, years ago has been done in several ways.
One way is to find yearly layers that are produced over longer periods of time than tree rings. In some lakes or bays where underwater sedimentation occurs at a relatively rapid rate, the sediments have seasonal patterns, so each year produces a distinct layer.
Such sediment layers are called "varves", and are described in more detail below. Varve layers can be counted just like tree rings.
If layers contain dead plant material, they can be used to calibrate the carbon ages. Another way to calibrate carbon farther back in time is to find recently-formed carbonate deposits and cross-calibrate the carbon in them with another short-lived radioactive isotope. Where do we find recently-formed carbonate deposits? If you have ever taken a tour of a cave and seen water dripping from stalactites on the ceiling to stalagmites on the floor of the cave, you have seen carbonate deposits being formed.
Since most cave formations have formed relatively recently, formations such as stalactites and stalagmites have been quite useful in cross-calibrating the carbon record. What does one find in the calibration of carbon against actual ages? If one predicts a carbon age assuming that the ratio of carbon to carbon in the air has stayed constant, there is a slight error because this ratio has changed slightly.
Figure 9 shows that the carbon fraction in the air has decreased over the last 40, years by about a factor of two.
This is attributed to a strengthening of the Earth's magnetic field during this time. A stronger magnetic field shields the upper atmosphere better from charged cosmic rays, resulting in less carbon production now than in the past. Changes in the Earth's magnetic field are well documented.
Complete reversals of the north and south magnetic poles have occurred many times over geologic history. A small amount of data beyond 40, years not shown in Fig. What change does this have on uncalibrated carbon ages? The bottom panel of Figure 9 shows the amount. Figure 9. Ratio of atmospheric carbon to carbon, relative to the present-day value top panel. Tree-ring data are from Stuiver et al. The offset is generally less than years over the last 10, years, but grows to about 6, years at 40, years before present.
Uncalibrated radiocarbon ages underestimate the actual ages. Note that a factor of two difference in the atmospheric carbon ratio, as shown in the top panel of Figure 9, does not translate to a factor of two offset in the age.
Rather, the offset is equal to one half-life, or 5, years for carbon The initial portion of the calibration curve in Figure 9 has been widely available and well accepted for some time, so reported radiocarbon dates for ages up to 11, years generally give the calibrated ages unless otherwise stated.
The calibration curve over the portions extending to 40, years is relatively recent, but should become widely adopted as well. It is sometimes possible to date geologically young samples using some of the long-lived methods described above.
These methods may work on young samples, for example, if there is a relatively high concentration of the parent isotope in the sample.
In that case, sufficient daughter isotope amounts are produced in a relatively short time. As an example, an article in Science magazine vol. There are other ways to date some geologically young samples. Besides the cosmogenic radionuclides discussed above, there is one other class of short-lived radionuclides on Earth.
These are ones produced by decay of the long-lived radionuclides given in the upper part of Table 1. As mentioned in the Uranium-Lead section, uranium does not decay immediately to a stable isotope, but decays through a number of shorter-lived radioisotopes until it ends up as lead. While the uranium-lead system can measure intervals in the millions of years generally without problems from the intermediate isotopes, those intermediate isotopes with the longest half-lives span long enough time intervals for dating events less than several hundred thousand years ago.
Note that these intervals are well under a tenth of a percent of the half-lives of the long-lived parent uranium and thorium isotopes discussed earlier. Two of the most frequently-used of these "uranium-series" systems are uranium and thorium These are listed as the last two entries in Table 1, and are illustrated in Figure Figure A schematic representation of the uranium decay chain, showing the longest-lived nuclides. Half-lives are given in each box. Solid arrows represent direct decay, while dashed arrows indicate that there are one or more intermediate decays, with the longest intervening half-life given below the arrow.
Like carbon, the shorter-lived uranium-series isotopes are constantly being replenished, in this case, by decaying uranium supplied to the Earth during its original creation. Following the example of carbon, you may guess that one way to use these isotopes for dating is to remove them from their source of replenishment.
This starts the dating clock. In carbon this happens when a living thing like a tree dies and no longer takes in carbonladen CO 2.
For the shorter-lived uranium-series radionuclides, there needs to be a physical removal from uranium. The chemistry of uranium and thorium are such that they are in fact easily removed from each other. Uranium tends to stay dissolved in water, but thorium is insoluble in water. So a number of applications of the thorium method are based on this chemical partition between uranium and thorium. Sediments at the bottom of the ocean have very little uranium relative to the thorium.
Because of this, the uranium, and its contribution to the thorium abundance, can in many cases be ignored in sediments. Thorium then behaves similarly to the long-lived parent isotopes we discussed earlier. It acts like a simple parent-daughter system, and it can be used to date sediments. On the other hand, calcium carbonates produced biologically such as in corals, shells, teeth, and bones take in small amounts of uranium, but essentially no thorium because of its much lower concentrations in the water.
This allows the dating of these materials by their lack of thorium. A brand-new coral reef will have essentially no thorium As it ages, some of its uranium decays to thorium While the thorium itself is radioactive, this can be corrected for. Comparison of uranium ages with ages obtained by counting annual growth bands of corals proves that the technique is.
The method has also been used to date stalactites and stalagmites from caves, already mentioned in connection with long-term calibration of the radiocarbon method. In fact, tens of thousands of uranium-series dates have been performed on cave formations around the world.
Previously, dating of anthropology sites had to rely on dating of geologic layers above and below the artifacts. But with improvements in this method, it is becoming possible to date the human and animal remains themselves.
Work to date shows that dating of tooth enamel can be quite reliable. However, dating of bones can be more problematic, as bones are more susceptible to contamination by the surrounding soils. As with all dating, the agreement of two or more methods is highly recommended for confirmation of a measurement. If the samples are beyond the range of radiocarbon e. We will digress briefly from radiometric dating to talk about other dating techniques.
It is important to understand that a very large number of accurate dates covering the pastyears has been obtained from many other methods besides radiometric dating. We have already mentioned dendrochronology tree ring dating above.
Dendrochronology is only the tip of the iceberg in terms of non-radiometric dating methods.
Here we will look briefly at some other non-radiometric dating techniques. Ice Cores. One of the best ways to measure farther back in time than tree rings is by using the seasonal variations in polar ice from Greenland and Antarctica. There are a number of differences between snow layers made in winter and those made in spring, summer, and fall. These seasonal layers can be counted just like tree rings.
The seasonal differences consist of a visual differences caused by increased bubbles and larger crystal size from summer ice compared to winter ice, b dust layers deposited each summer, c nitric acid concentrations, measured by electrical conductivity of the ice, d chemistry of contaminants in the ice, and e seasonal variations in the relative amounts of heavy hydrogen deuterium and heavy oxygen oxygen in the ice.
These isotope ratios are sensitive to the temperature at the time they fell as snow from the clouds. The heavy isotope is lower in abundance during the colder winter snows than it is in snow falling in spring and summer.TOP Radiometric Dating Proves God's Real! - Dr. Gene Kim
So the yearly layers of ice can be tracked by each of these five different indicators, similar to growth rings on trees. The different types of layers are summarized in Table III. Ice cores are obtained by drilling very deep holes in the ice caps on Greenland and Antarctica with specialized drilling rigs. As the rigs drill down, the drill bits cut around a portion of the ice, capturing a long undisturbed "core" in the process.
These cores are carefully brought back to the surface in sections, where they are catalogued, and taken to research laboratories under refrigeration. A very large amount of work has been done on several deep ice cores up to 9, feet in depth. Several hundred thousand measurements are sometimes made for a single technique on a single ice core. A continuous count of layers exists back as far asyears. In addition to yearly layering, individual strong events such as large-scale volcanic eruptions can be observed and correlated between ice cores.
A number of historical eruptions as far back as Vesuvius nearly 2, years ago serve as benchmarks with which to determine the accuracy of the yearly layers as far down as around meters. As one goes further down in the ice core, the ice becomes more compacted than near the surface, and individual yearly layers are slightly more difficult to observe.