Reliability of Geologic Dating

How Old is the Earth

approximately how old is the earth based on radioactive isotope dating

Modeled on an analogy to a liquid drop, the first term represents the favourable contribution to the binding of the nucleus made by short-range, attractive nuclear forces between neutrons and protons. The combination of these processes recycles the oceanic crust back into the mantle. Taylor, "Isotopic Compositions of the Elements ," J. Instability of the rings of Saturn 1,,

A Response to “Scientific” Creationism

Because of this problem, whole-rock isochrons are invalid, representing the original incomplete mixing of two or more sources. The highest air temperature ever measured on Earth was Virtually all the heat lost from the ocean basins comes from the mantle and is brought close to the surface by convection. The decrease in abundance with increasing mass reflects in part the successive nature of nucleosynthesis. Morris, Henry, and Gary Parker, Third, they use inappropriate depth distributions for the radioactive elements. In short, "different analytical approaches at different localities were used to work out 36 Cl production rates, which are discordant.

Morris and Parker 97 have blatantly misrepresented legitimate scientific data and conclusions. The present rate of offshore oil seepage cannot be used to calculate an age for the Earth. The reference for this age of the Earth is a short news item in Chemical and Engineering News , which, in its entirety, reads as follows:. Plutonium occurs in nature. Detection of this relatively short-lived isotope 80 million years may indicate that synthesis of heavy elements was still occurring at the time of formation of the Solar System.

The discovery of natural plutonium was significant partly because it was the heaviest isotope ever found in nature but mostly because it gave scientists a valuable clue about the time of synthesis of the heavy elements. The reasoning is as follows. Thus, the discovery of plutonium in nature suggests that it may have been synthesized as the Solar System formed rather than much earlier. What Morris and Parker 97 have listed as an million-year indicated age of the Earth is simply the half-life of plutonium Clearly, they do not understand either the content or the significance of the discovery reported in the brief news article they cite as their source of documentation.

This age is attributed to Barnes Barnes 14 summarizes and supports the arguments developed first in by Sir William Thomson Lord Kelvin , who calculated that the Earth could be no less than 20 million and no more than million years old Kelvin also calculated that the Sun is probably no more than million years old and almost certainly no more than million years old These upper limits for the age of the Sun were based on his estimate of the available supply of gravitational energy, which, he concluded, would not last many millions of years longer.

The value of 24 million years, preferred by Barnes 14 and listed by Morris and Parker 97 as the age of the Earth, is attributed by Barnes to Kelvin but was, in fact, first published by King The dispute was resolved in , when Rutherford and Soddy first determined the amount of heat generated by radioactive decay.

Rutherford and Soddy readily appreciated the significance of their discovery for cosmologic hypotheses:. It the energy from radioactive decay must be taken into account in cosmical physics. The maintenance of solar energy, for example, no longer presents any fundamental difficulty if the internal energy of the component elements is considered to be available, i.

Subsequent measurements of the amount of radioactive uranium, thorium, and potassium in the Earth and in meteorites have shown that all the heat flowing from the interior of the Earth outward can easily be accounted for by radioactive decay, although gravitational energy and latent heat of crystallization probably are also important.

Kelvin was well aware of radioactivity, as is demonstrated by the fact that he wrote several papers on it. That did not appear to him to alter the problem at all. The first statement is simply untrue. There is a large volume of literature on the subject of the thermal state and history of the Earth; most beginning geology textbooks treat the subject.

While it is true that Kelvin published several papers on radioactivity, these papers were unrelated to his age-of-the-earth calculations. Barnes implies that Kelvin considered the matter and concluded that it was unimportant.

In fact, Kelvin privately admitted that his hypothesis regarding the age of the Earth had been disproved by the discovery of the enormous amount of energy available from within the atom 21 , although he never recanted. Kelvin apparently realized that he had lost the argument and simply gave up, turning his energies to other matters until his death in The preth-century history of the various attempts by scientists and philosophers to estimate the age of the Earth is a fascinating subject that the reader may wish to explore in more detail 1 , In a recent creationist monograph, Slusher and Gamwell consider the contribution of radioactive heat to the problem of a cooling Earth and conclude that even with radioactivity as a source of heat, the calculations lead to the conclusion that the Earth is young:.

The cooling times appear quite small thousands of years if the initial temperature of the earth was on the order of that for a habitable planet for any of the models. Even for initial temperatures as high as that for an initially molten earth, the cooling times are vastly less than evolutionist estimates.

It would seem that the earth is vastly younger than the old earth demanded by the evolutionists. Thus, the evolutionary hypothesis would seem to be a false hypothesis for explaining things. Their treatment of this important and complex problem, however, is inexcusably naive.

They have neglected important sources of heat within the Earth, selected inappropriate depth distributions of radioactive elements, and ignored completely the loss of heat by convection in the mantle. The problem is complicated by several factors: There are several important sources of heat in the Earth. One is primordial heat, i. Although the Earth probably accreted cold, radioactivity, gravitational energy from compaction, and segregation of the iron-nickel core probably generated enough heat to raise the temperature of the Earth to near the melting point within to million years of its formation 83 , In addition, the heat from impacts of large meteorites during the period when the Earth was still sweeping up large amounts of material from its orbital path generated large amounts of heat and may have resulted in the melting of the outer km or so.

Much of this primordial heat has not yet escaped from the Earth. A second source of heat is radioactivity. This heat is generated by the radioactive decay of uranium, thorium, and potassium contained in the rocks of the Earth.

Although the exact distribution of these radioactive elements within the Earth is not well known, there is no problem in constructing reasonable Earth models that attribute most or even all of the heat now flowing outward from the Earth to radioactive decay.

For example, all the heat required could be generated by the uranium, thorium, and potassium contained in a granitic crust only 22 km thick Likewise, if we assume that the Earth has a bulk composition similar to that of the primitive meteorites called carbonaceous chondrites, then the heat produced by radioactivity would about equal the present average heat flux from the mantle These two examples, of course, are oversimplifications of a problem of vastly greater complexity, but they do illustrate that radioactivity is probably the single most important mechanism of heat generation in the Earth today.

Because radioactive elements decay exponentially over time, radioactive decay would have generated even more heat in the past. Of equal importance as heat sources are the mechanisms by which the Earth loses heat. One is conduction, which involves the transfer of kinetic energy at the atomic and molecular level; this is the same means by which heat is transferred through the bottom of a cooking pan from the burner to the food. The conductivity of rocks, however, is rather poor, and conduction is not particularly efficient.

For example, heat generated 4. The most important mechanism of heat loss from the Earth is convection, which involves the transfer of heat by motion of the hot material itself. Convection is highly efficient and, to a large degree, self-regulating. When a liquid is heated in a pan, for example, the more heat is supplied, the more vigorously the liquid convects, and the faster heat is lost.

Calculations show that the rocks of the mantle can be expected to show similar behavior; the more heat is supplied, the less viscous the mantle becomes, the faster it convects, and the more heat is transferred to the surface.

The evidence from continental drift, sea-floor spreading, and the bathymetry of the sea floor is conclusive. Calculations also show that mantle convection is both physically possible and probable. Although at first it may seem impossible for solid rocks to flow, both theory and laboratory experiments show that they can and do, although the mechanism differs somewhat from that involved in the flow of liquid.

Estimates of the present rate of mantle convection indicate that the motion is on the order of a millimeter or so per year. Studies of the thermal budget of the Earth consist of balancing the various heat sources against heat loss through convection and conduction, taking into consideration what is known about the history and physical properties of the Earth. The heat flow per unit area from the continents is about the same as from the oceans, although both local and regional variations occur.

Virtually all the heat lost from the ocean basins comes from the mantle and is brought close to the surface by convection. About 30 percent of the total global heat loss is at the midoceanic rises, where new crust is forming by the injection and eruption of magma 83 , Although conduction plays a role in transferring some heat through the oceanic crust, convection is the dominant mechanism bringing heat from depth.

In contrast, heat loss from the continents is primarily by conduction. Of this heat, about two-thirds is generated by radioactivity within the continents themselves ; the remainder is brought to the base of the continental lithosphere from the mantle by convection, where it is then conducted to the surface. They have reached this conclusion by ignoring most of what is known about the chemistry, physics, and history of the Earth.

First, they begin with the erroneous assumption that the only heat-loss mechanism for the Earth is conduction; they completely ignore convection. They take no account of the differences in either heat generation or loss between these vastly different regimes of the Earth.

Third, they use inappropriate depth distributions for the radioactive elements. Finally, thermal analysis of the Earth cannot yield an estimate of its age.

The age of the Earth, determined independently by radiometric dating, is one of the boundary conditions that must be satisfied in such an analysis; it is not a result. There are simply far too many things about the history and interior of the Earth that are poorly known and must be estimated.

For example, even before convection was known to be an important factor in heat loss from the Earth, scientists were able to devise reasonable thermal models for the Earth that attributed all the heat generated to radioactive decay and all the heat lost to conduction. This was done simply by choosing reasonable distributions and concentrations of radioactive elements that yielded a balance between generation and loss and preserved the observed geothermal gradient.

As new knowledge about mantle convection and the early history of the Earth accumulated, these models were changed to account for the new findings. Morris and Parker 97 list an age of the Earth of 5 million years based on the accumulation of calcareous ooze on the sea floor.

The reference for this age is a report by Ewing and others 45 The report by Ewing and his coworkers describes a study of the sediment distribution on the Mid-Atlantic Ridge. They found that the sediment there is quite thin and concluded that at the present rate of sedimentation, the sediment could have accumulated in about 2 to 5 million years.

This short time was puzzling to them because the ocean basins were then thought to be very old — their report was published before the theory of plate tectonics and sea-floor spreading was formulated, tested, and confirmed. We now know that the midoceanic ridges are very young and still active; in fact, their age is zero at the ridge crests.

The 2 to 5 million years calculated by Ewing and his coworkers is about right for that part of the ridge surveyed by them. Note that Ewing and his coworkers did not calculate an age for the Earth, nor did they produce or describe any data with which such a calculation could be made. Tektites are small globules of glass whose origin has been the subject of much debate but is now thought to be from meteoritic impacts on the Earth. Boeckl 18 was attempting to establish a cosmic-ray-exposure-age for these objects to determine their residence time in space.

To do so, he assumed a terrestrial age for the tektites of 10, years to make his calculations. Boeckl did not calculate an age for the Earth, nor did he produce any data that could be used to do so; Morris 93 , 95 even has the number wrong.

A simple bar magnet is one type of dipole. Lord Kelvin thought that the Earth was millions of years old, a view contrary to that of Barnes and his creationist colleagues Table 9. The final result, a 4. Since his area of the Earth 5. A look at the arguments used by Kent Hovind to "prove" that the Earth is young. An Index to Creationist Claims A comprehensive look at the claims of all kinds of creationists arguments including young-earth arguments not debunked in "How Old is the Earth.

Similar Lists Appear in Morris 93 , Process Indicated age of the Earth years Reference 1. Influx of radiocarbon to the Earth system 10, 29 3. Influx of meteoritic dust from space Too small to calculate 92 4.

Influx of juvenile water to the oceans ,, 92 5. Influx of magma from the mantle to form the crust ,, 92 6. Growth of oldest living part of the biosphere 5, 92 7. Origin of human civilizations 5, 92 8. Efflux of He into the atmosphere 1, - , 27 9. Development of the total human population 4, 94 Influx of sediment to the ocean via rivers 30,, 99 Erosion of sediment from the continents 14,, 99 Leaching of sodium from the continents 32,, Leaching of chlorine from the continents 1,, Leaching of calcium from the continents 12,, Influx of carbonate to the ocean , Influx of sulfate to the ocean 10,, Influx of chlorine to the ocean ,, Influx of calcium to the ocean 1,, Influx of uranium to the ocean 1,, 17 Efflux of oil from traps by fluid pressure 10, - , 28 Formation of radiogenic lead by neutron capture Too small to measure 28 Formation of radiogenic strontium by neutron capture Too small to measure 28 Decay of natural remanent paleomagnetism , 28 Decay of C in Precambrian wood 4, 28 Decay of potassium with entrapped argon Too small to measure Formation of river deltas 5, 4 Submarine oil seepage into the ocean 50,, Decay of natural plutonium 80,, 7 Decay of lines of galaxies 10,, 9 Expanding interstellar gas 60,, 68 Decay of short-period comets 10, Decay of long-period comets 1,, Influx of small particles to the Sun 83, Maximum life of meteor showers 5,, Accumulation of dust on the Moon , Instability of the rings of Saturn 1,, Escape of methane from Titan 20,, Deceleration of the earth by tidal friction ,, 14 Cooling of the Earth by heat efflux 24,, 14 Accumulation of calcareous ooze on the sea floor 5,, 45 Influx of sodium to the ocean via rivers ,, 22 , Influx of nickel to the ocean via rivers 9, 22 , Influx of magnesium to the ocean via rivers 45,, 22 , Influx of silicon to the ocean via rivers 8, 22 , Influx of potassium to the ocean via rivers 11,, 22 , Influx of copper to the ocean via rivers 50, 22 , Influx of gold to the ocean via rivers , 22 , Influx of silver to the ocean via rivers 2,, 22 , Influx of mercury to the ocean via rivers 42, 22 , Influx of lead to the ocean via rivers 2, 22 , Influx of tin to the ocean via rivers , 22 , Influx of aluminum to the ocean via rivers 22 , Influx of lithium to the ocean via rivers 20,, 22 , Influx of titanium to the ocean via rivers 22 , Influx of chromium to the ocean via rivers 22 , Influx of manganese to the ocean via rivers 1, 22 , Influx of iron to the ocean via rivers 22 , Influx of cobalt to the ocean via rivers 18, 22 , Influx of zinc to the ocean via rivers , 22 , Influx of rubidium to the ocean via rivers , 22 , Influx of strontium to the ocean via rivers 19,, 22 , Influx of bismuth to the ocean via rivers 45, 22 , The explanation of the apparent paradox is that nuclides in this category are continually replenished by specialized nuclear processes: Nuclear testing and the release of material from nuclear reactors also introduce radioactive isotopes into the environment.

Nuclear physicists have expended great effort to create isotopes not detected in nature, partly as a way to test theories of nuclear stability. Like most isotopes of elements heavier than uranium, it is radioactive, decaying in fractions of a second into more-common elements. The composition of any object can be given as a set of elemental and isotopic abundances. One may speak, for example, of the composition of the ocean, the solar system, or indeed the Galaxy in terms of its respective elemental and isotopic abundances.

Formally, the phrase elemental abundances usually connotes the amounts of the elements in an object expressed relative to one particular element or isotope of it selected as the standard for comparison. Isotopic abundances refer to the relative proportions of the stable isotopes of each element. They are most often quoted as atom percentages, as in the table. Since the late s, geochemists, astrophysicists, and nuclear physicists have joined together to try to explain the observed pattern of elemental and isotopic abundances.

A more or less consistent picture has emerged. Hydrogen, much helium, and some lithium isotopes are thought to have formed at the time of the big bang—the primordial explosion from which the universe is believed to have originated. The rest of the elements come, directly or indirectly, from stars. Cosmic rays produce a sizable proportion of the elements with mass numbers between 5 and 10; these elements are relatively rare.

A substantial body of evidence shows that stars synthesize the heavier elements by nuclear processes collectively termed nucleosynthesis. In the first instance, then, nucleosynthesis determines the pattern of elemental abundances everywhere. The pattern is not immutable, for not all stars are alike and once matter escapes from stars it may undergo various processes of physical and chemical separation.

A newly formed small planet, for example, may not exert enough gravitational attraction to capture the light gases hydrogen and helium.

On the other hand, the processes that change elemental abundances normally alter isotopic abundances to a much lesser degree. Thus, virtually all terrestrial and meteoritic iron analyzed to date consists of 5.

The table lists the isotopic abundances of the stable elements and of a few radioactive elements as well. The relative constancy of the isotopic abundances makes it possible to tabulate meaningful average atomic masses for the elements. The availability of atomic masses is very important to chemists.

While there is general agreement on how the elements formed, the interpretation of elemental and isotopic abundances in specific bodies continues to occupy the attention of scientists.

They obtain their raw data from several sources. Most knowledge concerning abundances comes from the study of the Earth, meteorites, and the Sun. Currently accepted estimates of solar system as opposed to terrestrial abundances are pieced together mainly from two sources.

Chemical analyses of Type I carbonaceous chondrites , a special kind of meteorite, provide information about all but the most volatile elements—i.

Spectroscopic analysis of light from the Sun furnishes information about the volatile elements deficient in meteorites. To the extent that the Sun resembles other stars, the elemental and isotopic abundances of the solar system have universal significance. The solar system pattern has several notable features.

First, the lighter isotopes, those of hydrogen and helium, constitute more than 98 percent of the mass; heavier isotopes make up scarcely 2 percent. Second, apart from the exceptions discussed below, as A or Z increases through the periodic table of the elements, abundances generally decrease.

For example, the solar system as a whole contains about one million times more carbon, nitrogen , and oxygen than the much heavier elements platinum and gold , though the proportions of the latter may vary widely from object to object. The decrease in abundance with increasing mass reflects in part the successive nature of nucleosynthesis.

In nucleosynthesis a nuclide of lower mass often serves as the seed or target for the production of a nuclide of higher mass. As the conversion of the lower mass target to the higher mass product is usually far from complete, abundances tend to decrease as mass increases.

A third feature of interest is that stable isotopes with even numbers of protons and neutrons occur more often than do isotopes with odd ones the so-called odd-even effect. Out of the almost stable nuclides known, only five have odd numbers of both protons and neutrons; more than half have even values of Z and N. Fourth, among the isotopes with even Z and N certain species stand out by virtue of their considerable nuclear stability and comparatively high abundances. Finally, peaks in the abundance distribution occur near the special values of Z and N defined above as magic numbers.

The high abundances manifest the extra nuclear stability that the magic numbers confer. The study of cosmic rays and of the light emitted by stars yields information about elemental and isotopic abundances outside the solar system. Cosmic rays are atomic nuclei or electrons with high energy that generally come from outside the solar system. The Sun produces cosmic rays too, but of much lower average energy than those reaching the solar system from outside. The abundance pattern in cosmic rays resembles that of the solar system in many ways, suggesting that solar and overall galactic abundances may be similar.

Two explanations have been advanced to account for why solar and cosmic-ray abundances do not agree in all respects. The first is that cosmic rays undergo nuclear reactions, i.

The second is that material from unusual stars with exotic compositions may be more prominent in cosmic rays. The determination of elemental and isotopic abundances in stars of the Milky Way Galaxy and of more-distant galaxies poses formidable experimental difficulties. Research in the field is active and reveals trends in composition among stars that are consistent with nucleosynthetic theory. In addition, many stars with compositions far different from that of the solar system are known.

Their existence has led some investigators to doubt whether the concept of cosmic, as opposed to solar-system, abundances is meaningful. For the present it is perhaps enough to quote the American astrophysicist James W. The local pattern of abundances is generally representative.

The gross abundance features throughout our galaxy, in other galaxies, and even apparently in quasars are generally similar to those of solar system matter, testifying to the fact that the underlying stellar systems share the same nucleosynthetic processes. Mass spectrometers are well suited to the measurement of isotopes, but they have difficulty in resolving isobars of nearly equal masses.

Isotope s are all atoms of an element that have unequal mass but the same atomic number. Isotope s of the same element are virtually identical chemically. Isotope s are forms of an element that are chemically indistinguishable from each other but differ in physical properties. Careful experimental examination of naturally occurring samples of many pure elements shows that not all the atoms present have the same atomic weight, even though they all have the same atomic number.

Such a situation can occur only if the atoms have different numbers…. Most elements exist in different atomic forms that are identical in their chemical properties but differ in the number of neutral particles— i.

For a single element, these…. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval.

Unfortunately, our editorial approach may not be able to accommodate all contributions. Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. Abundances of the isotopes Sources: Taylor, "Isotopic Compositions of the Elements ," J.

Data 27, — Page 1 of 3. Next page Variations in isotopic abundances. Learn More in these related articles: Cosmic-ray exposure ages of meteorites applications absolute dating In dating: Principles of isotopic dating centrifugation In centrifuge: Vacuum-type centrifuges climatic change and geochronology In Pleistocene Epoch: Marine oxygen isotope record earth evolution studies In Earth: Accretion of the early Earth mass spectrometry In mass spectrometry: Atomic masses metabolism In metabolism: The study of metabolic pathways nuclear fission In nuclear fission: Fission decay chains and charge distribution resonance-ionization mass spectrometry In spectroscopy: Resonance-ionization mass spectrometry chemical elements In chemical element: The existence of isotopes View More.

Articles from Britannica Encyclopedias for elementary and high school students. Help us improve this article! Contact our editors with your feedback. Introduction The discovery of isotopes Nuclear stability Radioactive isotopes Elemental and isotopic abundances Variations in isotopic abundances Radioactive decay Mass fractionation Other causes of isotopic abundance variations Physical properties associated with isotopes Effect of isotopes on atomic and molecular spectra Molecular vibrations Importance in the study of polyatomic molecules Chemical effects of isotopic substitution Effect of isotopic substitution on reaction rates Isotope separation and enrichment Mass spectrometry Distillation Chemical exchange reactions Gaseous diffusion Gas centrifugation Photochemical enrichment methods.

Imsges: approximately how old is the earth based on radioactive isotope dating

approximately how old is the earth based on radioactive isotope dating

Back to Magnetic decay or Moon dust. Archived from the original on 13 July Bloch, in fact, has carefully determined the effect of all such possibilities.

approximately how old is the earth based on radioactive isotope dating

The majority of scientists today assume that the dates they give indicate the time the magma cooled. The vast extent and sheer volume of such individual flows are orders of magnitude larger than anything ever recorded in known human history.

approximately how old is the earth based on radioactive isotope dating

Note that Ewing and his coworkers did not calculate an age for the Earth, nor did they produce or describe any data with which such a calculation could be made. However, the lunar soil is not the only meteoritic material on the lunar surface. This article is about the planet itself. Fission track dating is a radioisotopic dating method that depends on the tendency of uranium Uranium to undergo spontaneous fission as well as the usual decay process. When the massive impact creates a lot of heat, which melts the rocks of the Earth and send them hurtling through the atmosphere at incredible speed. Zircon age calculations on the base of Upb systematics have been complicated weatherford texas dating high share of common Pb and benefits of dating a military man of its isotope composition. Although the Earth probably accreted cold, radioactivity, gravitational energy from compaction, and segregation of the iron-nickel core probably generated enough heat to raise the temperature of the Earth to near the melting point within to million years of its formation 83