Historical Geology/Absolute dating: an overview - Wikibooks, open books for an open world
Review Quiz When using radiometric dating to determine the absolute age of a rock, Which set of relative dating methods is most useful to determine the. This quiz will test your understanding of determining relative ages of rock layers, absolute ages of rock layers as well as using fossils for dating. Radioactive Dating - Essential Question How could you create a product that helps of rocks and fossils from index fossils and ordering of rock layers on a test? Dating Lab and answer the following questions: 1) What is the relative dating?.
How is the boundary between the two formations best described? A fault plane c.Relative/Absolute Dating
A nonconformity A geologist examines a layer of sedimentary rock strata that contains pebbles of granite. From this, the geologist could infer that: An older layer of granite is below the sedimentary rock b. An older layer of granite is above the sedimentary rock c. A younger layer of granite is below the sedimentary rock d. A younger layer of granite is above the sedimentary rock Which would generally NOT be involved in determining the relative age of rock strata?
Rule of superposition d. Cross-cutting relationships Which shows the correct order, from oldest to youngest, of the relative ages of the formations shown?
D, C, B, A How does the principle of uniformitarianism differ from earlier views of the geologic processes that have shaped Earth? It claims that the structures on Earth are gradually becoming more uniform in shape and composition. It proposes that only gradual, slowly occurring, natural processes can significantly affect the structures on Earth.
It suggests that the processes currently shaping the Earth are the same processes that shaped Earth throughout its history. It has also been possible to test Ar-Ar dating against the historical record, since it is sufficiently sensitive to date rocks formed since the inception of the historical record. For example, Ar-Ar dating has been used to give an accurate date for the eruption of Vesuvius in 79 A. D, as recorded by Roman historians at the time. See Lanphere et al.
Historical Geology/Absolute dating: an overview
Radiocarbon dating, varves, and dendrochronology[ edit ] Because varves contain organic material, it is possible to compare the dates from varves with the dates produced by radiocarbon datingand see that they are in good agreement. We also see close agreement between dendrochronology and uncalibrated radiocarbon dates.
I specify uncalibrated dates because as radiocarbon dating is calibrated against dendrochronologythe agreement of calibrated radiocarbon dates with dendrochronology is inevitable. Now, each of these three methods relies on a different underlying physical process: 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 concordantnamely that they are correct. Radiometric dating, sclerochronology and rhythmites[ edit ] Similar remarks may be made about the agreement between radiometric dating of rocks, sclerochronologyand dating by rhythmites. Are we to believe that one single mechanism interfered with the decay of radioactive isotopesthe 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?
Geological Dating - ProProfs Quiz
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?
Agreement with relative dating[ edit ] 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.
Internal consistency of radiometric dates[ edit ] In our discussion of radiometric datingwe have seen that many, indeed most, radiometric methods are self-checking. So in the U-Pb methodwe check that the two uranium isotopes produce concordant dates.
In the Ar-Ar methodwe 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, weatheringhydrothermal events, metamorphismmetasomatismetc.
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.
Mutual consistency of radiometric dates[ edit ] 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.