Scientist of the Day – Clair Patterson
Uranium-lead dating computes the age of the earth at 4. It is one of the oldest and most refined radiometric dating schemes, with a routine age range of about 1 million years to over 4. The method relies on the coupled chronometer provided by the decay of U to Pb, with a half-life of 4. One of the advantages of uranium-lead dating is the two separate, chemically identical chronometers and is accepted as the most reliable measurement of the age of the Earth. Loss leakage of lead within the sample will result in a discrepancy in the two decay schemes, resulting in a different age determined by each decay scheme. This effect is referred to as discordance, and provides a check on the reliability of the age. The presence of minerals or zones within minerals, older than the rock being dated can also cause age-discordance. In either case, the geochronologist is warned that such uranium-lead ages cannot be taken at face value.
Planet Earth doesn’t have a birth certificate to record its formation, which means scientists spent hundreds of years struggling to determine the age of the planet. So, just how old is Earth? By dating the rocks in Earth’s ever-changing crust, as well as the rocks in Earth’s neighbors, such as the moon and visiting meteorites, scientists have calculated that Earth is 4.
Zircon contains the radioactive element uranium, which Dr. Mueller calls “the clock within the zircon” because it converts to the element lead at a specific rate.
In , shortly after the discovery of radioactivity , the American chemist Bertram Boltwood suggested that lead is one of the disintegration products of uranium, in which case the older a uranium-bearing mineral the greater should be its proportional part of lead. Analyzing specimens whose relative geologic ages were known, Boltwood found that the ratio of lead to uranium did indeed increase with age.
After estimating the rate of this radioactive change, he calculated that the absolute ages of his specimens ranged from million to 2. Though his figures were too high by about 20 percent, their order of magnitude was enough to dispose of the short scale of geologic time proposed by Lord Kelvin. Versions of the modern mass spectrometer were invented in the early s and s, and during World War II the device was improved substantially to help in the development of the atomic bomb.
Soon after the war, Harold C. Urey and G. Wasserburg applied the mass spectrometer to the study of geochronology. This device separates the different isotopes of the same element and can measure the variations in these isotopic abundances to within one part in 10, By determining the amount of the parent and daughter isotopes present in a sample and by knowing their rate of radioactive decay each radioisotope has its own decay constant , the isotopic age of the sample can be calculated.
For dating minerals and rocks, investigators commonly use the following couplets of parent and daughter isotopes: thorium—lead, uranium—lead, samarium—neodymium, rubidium—strontium, potassium—argon, and argon—argon The SHRIMP Sensitive High Resolution Ion Microprobe enables the accurate determination of the uranium-lead age of the mineral zircon, and this has revolutionized the understanding of the isotopic age of formation of zircon-bearing igneous granitic rocks.
Another technological development is the ICP-MS Inductively Coupled Plasma Mass Spectrometer , which is able to provide the isotopic age of the minerals zircon, titanite, rutile, and monazite. These minerals are common to many igneous and metamorphic rocks.
How is Earth’s Age Calculated?
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes. This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Over naturally-occurring isotopes are known.
Dating meteorites thus allows us to give a lower age to the Solar System (4,56 billion years old). Solar System. Lead isotope isochron that Clair Patterson used.
But is radioactive dating valid? With decades of experience in top nuclear physics laboratories, Dr. Vernon Cupps tackles this question from a scientific and biblical perspective.
How Old is Earth, and How Do We Know?
This is a learning project for exploration of scientific methods that have been used to measure the age of the Earth. Until the Scientific revolution there was no way for people to systematically explore the age of the Earth. People in some cultures imagined that the Earth was very old maybe even infinitely old and others imagined that it was young, possibly only a few thousand years old. Even after modern science began to develop in Western Europe, exploration of topics such as the age of the Earth was inhibited by cultural momentum.
Rethinking Radiometric Dating goes into detail about the major radiometric dating methods, Earth’s magnetic field, radiohalos, zircons, and soft tissue in fo. methods, including potassium-argon, rubidium-strontium, uranium-lead, and others.
You may have heard that the Earth is 4. This was calculated by taking precise measurements of things in the dirt and in meteorites and using the principles of radioactive decay to determine an age. This page will show you how that was done. Radioactive nuclides decay with a half-life. If the half-life of a material is years and you have 1 kg of it, years from now you will only have 0. The rest will have decayed into a different nuclide called a daughter nuclide.
Several radioactive nuclides exist in nature with half-lives long enough to be useful for geologic dating. This nuclide decays to Strontium Sr87 with a half-life of Imagine going way back in time and looking at some lava that is cooling to become a rock. This is shown schematically in Figure 1.
Rethinking Radiometric Dating
What is the role of geochronology in Earth and planetary sciences? Refinements in uranium-lead dating of zircon can date crystallization.
At around the same time that Arthur Holmes published his ideas for the age of the Earth, Harrison Brown, a professor at the University of Chicago, was developing a new method for counting lead isotopes in igneous rocks. Brown thought this method of counting was incredibly tedious but very easy, so he assigned it to Patterson as his dissertation project in Prior to beginning his research, Patterson had worked on the Manhattan Project during World War II, showing that, by the time he began his research, he had much experience in the field.
The main problem with using this method of dating was that Patterson needed ancient rocks that contained crystals bearing both uranium and lead. Additionally, these lead- and uranium-bearing crystals would have had to be as old as the Earth. In order to move past this problem, Patterson looked for answers in rocks beyond the Earth; he turned to meteorites. In using meteorites to calculate the age of the Earth, Patterson made two assumptions about rocks that proved to be correct.
He assumed, just as Holmes did, that meteorites were leftover materials from the beginning of the solar system and that by being in space, they would maintain an unchanged interior chemistry. Patterson believed, and rightfully so, that if he were to measure the age of one of these meteorites, then he would have an age close to that of the Earth. Patterson was able to acquire these rare meteorite samples, which contained zircon crystals.
These crystals were small and difficult to isolate, but they contained lead and uranium, the materials necessary for Patterson to conduct his research. However, he always found that they were contaminated with atmospheric lead when exposed to air. This allowed him to make more accurate measurements with clean samples. Patterson had received his Ph.
The following radioactive decay processes have proven particularly useful in radioactive dating for geologic processes:. Note that uranium and uranium give rise to two of the natural radioactive series , but rubidium and potassium do not give rise to series. They each stop with a single daughter product which is stable. Some of the decays which are useful for dating, with their half-lives and decay constants are:.
Which element is used by earth scientists for radioactive dating of rocks Isotopes what radioactive dating or earth page 25b dating technique. State of Green (project lead), the Confederation of Danish Industry, Quercus Group, Climate-KIC.
Dating , in geology , determining a chronology or calendar of events in the history of Earth , using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques. These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.
Radiometric dating and certain other approaches are used to provide absolute chronologies in terms of years before the present. The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere. Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.
This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil. For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built. Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.
Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information. A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered.
It should be emphasized that linking sites together is essential if the nature of an ancient society is to be understood, as the information at a single location may be relatively insignificant by itself.
The Age of the Earth
How Old is That Rock? How can you tell the age of a rock or to which geologic time period it belongs? One way is to look at any fossils the rock may contain. If any of the fossils are unique to one of the geologic time periods, then the rock was formed during that particular time period. Another way is to use the “What’s on top?
For centuries scholars sought to determine Earth’s age, but the answer when Archbishop James Ussher of Ireland offered the date of B.C. as the decay of uranium to helium versus its decay to lead) sometimes gave.
The same was long true of the cosmos. The ancient Greeks Eratosthenes and Aristarchus measured the size of the Earth and Moon, but could not begin to understand how old they were. With space telescopes, we can now even measure the distances to stars thousands of light-years away using parallax, the same geometric technique proposed by Aristarchus, but no new technology can overcome the fundamental mismatch between the human lifespan and the timescales of the Earth, stars, and universe itself.
Despite this, we now know the ages of the Earth and the universe to much better than 1 percent, and are beginning to date individual stars. Our ability to measure ages, to place ourselves in time as well as in space, stands as one of the greatest achievements of the last one hundred years. In the Western world, the key to the age of the Earth was long assumed to be the Bible and its account of creation.
Creation dating required careful accounting of the chronology given in Genesis and then matching it to historical events recorded elsewhere. These estimates were not seriously challenged until the emergence of modern geology in the eighteenth century. In the mids, the Scottish geologist James Hutton proposed that the processes of erosion, sedimentation, and volcanism that we observe today happened much the same way in the past.
Acting over many millions of years, they could explain the geological record without recourse to the great flood of Noah. Charles Lyell popularized the concept of uniformitarianism in the mids and argued that the Earth had to be very old indeed. More generally, uniformitarianism holds that the physical laws and processes we see today are the key to understanding the past.
Lead Isotopes and the Age of the Earth
Aristotle thought the earth had existed eternally. Roman poet Lucretius, intellectual heir to the Greek atomists, believed its formation must have been relatively recent, given that there were no records going back beyond the Trojan War. The Talmudic rabbis, Martin Luther and others used the biblical account to extrapolate back from known history and came up with rather similar estimates for when the earth came into being. Within decades observation began overtaking such thinking.
In the s Nicolas Steno formulated our modern concepts of deposition of horizontal strata.
His specialty was geochronology–the dating of the Earth. a rock with the amount of its radioactive decay byproduct, a specific isotope of lead.
Radiometric dating finds Earth is 2. This amazing fact seemed like alchemy to many, but American chemist Bertram Borden Boltwood was intrigued. Boltwood studied this concept of “radioactive series,” and found that lead was always present in uranium and thorium ores. He believed that lead must be the final product of the radioactive decay of uranium and thorium. A few years later, in , he reasoned that since he knew the rate at which uranium breaks down its half-life , he could use the proportion of lead in the uranium ores as a kind of meter or clock.
The clock would tell him how long that ore — and by extension, the earth’s crust — had existed. His observations and calculations put Earth’s age at 2. This was a dramatic increase in the estimate of Earth’s age for the time.