Types of Absolute Age Dating
We can hardly suppose that there is some single mechanism which would interfere with all three of these very different processes in such a way as to leave the dates derived from them still concordant. But it is equally far-fetched to imagine that three different mechanisms interfered with the three processes in such a way as to leave the dates concordant ; that would require either a preposterous coincidence, or for natural processes to be actually conspiring to deceive us: Now, preposterous things do happen occasionally. But in this case there is a perfectly reasonable and straightforward explanation for why the dates are concordant , namely that they are correct.
Similar remarks may be made about the agreement between radiometric dating of rocks, sclerochronology , and dating by rhythmites.
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Are we to believe that one single mechanism interfered with the decay of radioactive isotopes , the secretion of calcium carbonate by molluscs, and the action of the tide? But are we instead to believe that three separate mechanisms interfered with these processes in such a way as to leave all the dates concordant?
That would be equally absurd. The straightforward explanation for the concordance of the dates is that they are in fact correct. Consider the following analogy: Skeptical of the clockmaker's claim, we subject the clocks to shock: Throughout this process, they all go on showing exactly the same time. Is it plausible that we have damaged their very different internal mechanisms in such a way that they are all running fast or slow but still in perfect synchrony? Or is it more likely that they are synchronized because nothing that's happened to them has affected their working?
Relative dating by definition does not produce actual dates, but it does allow us to put an order on the rocks, and so if absolute dating is to be trusted, it should agree with this order, telling us, for example, that Ordovician rocks are older than Triassic rocks; and it does. It is hard to see this as a coincidence; it is equally hard to think of some alternate explanation of why we can correlate isotope ratios or sclerochronological data with the relative order of rocks as deduced from stratigraphic methods — other than the straightforward explanation that absolute dating is producing the right dates.
In our discussion of radiometric dating , we have seen that many, indeed most, radiometric methods are self-checking. So in the U-Pb method , we check that the two uranium isotopes produce concordant dates. In the Ar-Ar method , we check that step heating yields the same date at every step. These precautions allow us to throw out most data that have been produced by confounding factors such as atmospheric contamination, weathering , hydrothermal events, metamorphism , metasomatism , etc.
It is, as we have explained, possible for the occasional incorrect date to slip through this filter, since it is possible for some of these confounding factors to accidentally change the isotope ratios in such a way as to produce something that looks like a good date: It would indeed be remarkable if this never happened, since one-in-a-thousand chances do in fact occur one time in a thousand. But by the same token, the other times they don't, and so although any particular date produced by these methods might be called into question, it must be the case that the vast majority of dates that pass through these filters must be good; for we can hardly suppose that the confounding factors are actively conspiring to deceive us, and so these long-shot events must be as rare as statistical considerations would lead us to expect.
You might perhaps suggest that if some unknown factor, contrary to our present understanding of physics existed that sped up or slowed down radioactive decay in the past, then we would expect the radiometric dates to be concordant whether they were right or wrong. This is, as I say, contrary to our present understanding of physics, and so is mere unfounded speculation. What is more, the reader should recollect that " radioactive decay " is not the name of one process; it is the name of any process that rearranges the nucleus.
So to leave dates produced by different radiometric methods still concordant, nature would somehow have to conspire to fool us by changing the rates of alpha decay , of beta decay , and of electron capture , in such a way that the different dating methods based on these different modes of decay come up with the same dates.
Another point to bear in mind is that a change in the rate of radioactive decay, even if it was carefully coordinated in this way, would still not change every radiometric date in the same direction: It is possible to doubt any particular date obtained by absolute dating methods. But it would be bizarre to doubt the general picture they paint. For what we see is a massive agreement between the different radiometric methods , varves , dendrochronology , sclerochronology , rhythmites , paleomagnetic data, deposition rates, sea floor spreading , and relative dating methods.
For the dates obtained by absolute dating to be wrong in general and yet wrong in such a way as to be in agreement with one another and with other observations, we would have to suppose either that we are looking at an inconceivably massive coincidence, or that the whole Earth is a fraud designed to deceive us.
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Ideas to the latter effect have actually been proposed from time to time; most notably by the nineteenth century religious zealot Philip Gosse, whose eccentric work Omphalos proposed that the Earth was a mere few thousand years old, but that God had created it to look much older. To this the Reverend Charles Kingsley memorably answered: That of course would be a theological rather than a geological question, and so is outside the scope of this textbook.
What can be said is that geology is a science, and that in science it is necessary to proceed on the basis that the universe is not a lie; because if we believed that, we could believe that anything at all was the case and disregard all evidence to the contrary. The scientific method compels us, then, to disregard the possibility of divine malice; and mere natural processes, being mindless, cannot be actually malevolent. It is based on the concept that the lowest layer is the oldest and the topmost layer is the youngest.
Absolute dating
An extended version of stratigraphy where the faunal deposits are used to establish dating. Faunal deposits include remains and fossils of dead animals. This method compares the age of remains or fossils found in a layer with the ones found in other layers. The comparison helps establish the relative age of these remains.
Bones from fossils absorb fluorine from the groundwater. The amount of fluorine absorbed indicates how long the fossil has been buried in the sediments.
This technique solely depends on the traces of radioactive isotopes found in fossils. The rate of decay of these elements helps determine their age, and in turn the age of the rocks. Physical structure of living beings depends on the protein content in their bodies. The changes in this content help determine the relative age of these fossils. Each tree has growth rings in its trunk. This technique dates the time period during which these rings were formed.
Absolute Age: Definition & Dating | pcppk.com
It determines the period during which certain object was last subjected to heat. It is based on the concept that heated objects absorb light, and emit electrons. The emissions are measured to compute the age. Differentiation Using a Venn Diagram.
A Venn diagram depicts both dating methods as two individual sets. The area of intersection of both sets depicts the functions common to both. Take a look at the diagram to understand their common functions. When we observe the intersection in this diagram depicting these two dating techniques, we can conclude that they both have two things in common: Provide an idea of the sequence in which events have occurred.
Determine the age of fossils, rocks, or ancient monuments. Although absolute dating methods determine the accurate age compared to the relative methods, both are good in their own ways. Relative Dating Techniques Explained.