In age dating, wat rocks led scientist ascribe to the earth and solar system 4.56 billion years?

Question

The absolute age dting of what rocks/materials has led sceintist to ascribe to the earth and solar system an age of about 4.56 billion years?

Answer 1

Scientists have settled on the age of the earth of about 4.6 billion years as a result of research started almost 50 years ago. This conclusion was based upon carefully designed and conducted experiments that compared the ratios in rock samples of parent elements to daughter elements ( some of which would have been from radioactive decay of the parent, some of which may have been present in the sample at the time of formation). Since radioactive decay is known to occur at a constant rate, the age of a rock can be determined from the ratio of the parent element to the daughter element. The concerns about these dating methods were exactly the same that creationists continue to raise - presence of the daughter element at the time the rock was formed and possible loss / gain of either the parent or daughter element at some point in the history of the rock. For this reason, the tests were designed to account for those possibilities.

Initial daughter element can often be accounted for by either measuring the amount of an isotope of the daughter element (the ratio of isotopes are almost always constant). Another possibility is (as in the case of the potassium - argon - K-Ar method) that because the daughter element is gaseous, it would escape from the rock when the rock was molten. Once the rock cooled, the gaseous daughter would be trapped in the rocks crystal structure and could no longer escape. By experimentation, scientists have determined which rocks are suitable for various dating techniques. For K-Ar, for example, igneous rocks are good candidates for testing because they formed directly from molten magma and have a simple history. Metamorphic rocks do not work well because heating events in their history have allowed the escape of Argon (daughter element) and thus will indicate an age too young for the sample. Sedimentary rocks do not work because they are made up of a mixture of deposits of many other types of rocks, each of which would point to a different age. At any rate, scientists have devoted a great deal of effort to determining exactly which dating methods are appropriate for which types of rocks.

The other problem to avoid when dating rocks is the possibility that changes to the rock have caused loss or gain of either the parent or daughter element - this would lead to a false date (too old if parent element were lost, too young if daughter element were lost). I know of two methods that have been designed that can account for this possibility - isochron dating and the uranium-thorium-lead discordia / concordia method (actually three independent age calculations for one sample). Both of these methods have internal checks for the possible loss / gain of elements to the rock.

Creationists want the world to think that geologists just grab a rock and throw any old radiometric test at it and poof - there's the age of the rock. Reality is far more complex. If you examine the extensive research in the field of geochronology, you will see that one of the most important criteria in dating a sample lies in choosing an appropriate dating method for the sample. From G. Brent Dalrymple (see below):

One of the principal tasks of the geochronologist is to select the type of the material used for a dating analysis. A great deal of effort goes into the sample selection, and the choices are made before the analysis, not on the basis of the results. Mistakes are sometimes made but are usually caught by the various checks employed in the well-designed experiment.

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 include:

The Earths Oldest Rock's
Description Technique Age (in billions of years)

Amitsoq gneisses (western Greenland) Rb-Sr isochron 3.70 +- 0.12
Amitsoq gneisses (western Greenland) 207Pb-206Pb isochron 3.80 +- 0.12
Amitsoq gneisses (western Greenland) (zircons) U-Pb discordia 3.65 +- 0.05
Amitsoq gneisses (western Greenland) (zircons) Th-Pb discordia 3.65 +- 0.08
Amitsoq gneisses (western Greenland) (zircons) Lu-Hf isochron 3.55 +- 0.22
Sand River gneisses (South Africa) Rb-Sr isochron 3.79 +- 0.06

These are the oldest of the rocks dated on the earth so far (as of 1997). These are metamorphic rocks and thus have had some of their "history" lost - metamorphosis fully or partially resets the radiometric ages of rocks pointing to younger ages than the true age of the original rock. Older rocks may have been lost due to erosion or have not yet been discovered.

For many more examples of the consistancy of dating the same rocks with multiple methods, see Consistent Radiometric Dates by Joe Meert, a Geologist at the University of Florida. Dr. Meert's examples not only show that multiple radiometric methods come up with consistent dates for samples from the same locations, but that these results are also consistant with the paleomagnetic signature of the rocks, the position where the rocks would be expected to be (due to continental drift) at the time they were formed, and the cooling curves for the rocks. (Cooling curves deal with the fact that the different radiometric isotopes become "frozen" in the rocks at different temperatures. The higher the closure temperature for an isotope, the older the rock will be as dated by that isotope.) All of this consistancy rules out all of the arguments creationists attempt to make against radiometric dating techniques.
http://www.gate.net/~rwms/AgeEarth.html

Scientists also use geological principals to give relative dates to gelogical strata. http://homepage.usask.ca/~mjr347/prog/geoe118/geoe118.039.html
http://www.indiana.edu/~ensiweb/lessons/varves.html

Last but not least, scientists also use the Paleomagnetism studies of the ocean floor, which chronicles many polar shifts during the changing history of the ocean floor, to determine the age of the earth.

All of these methods, used independently, give the same approximate age of the earth; 4.56 billion years..

Answer 2

Obviously the very old rocks that they were testing. It is an estimate, you are not going to get an exact answer to something like that. There is empirical evidence though that proves beyond a reasonable doubt that the Earth is over 8,000 years old (as some religions purport).

The Chinese have a written history that is over 10,000 years.

Answer 3

U/Pb dating on chondritic meteorites.

Answer 4

yes it is so
and it is ture rock material in which bones and remains of human are present
and layers of rocks reveal this information