Earth scientists have devised many complementary and consistent techniques to estimate the ages of geologic events. Annually deposited layers of sediments or ice document hundreds of thousands of years of continuous Earth history. Gradual rates of mountain building, erosion of mountains, and the motions of tectonic plates imply hundreds of millions of years of change. Radiometric dating, which relies on the predictable decay of radioactive isotopes of carbon, uranium, potassium, and other elements, provides accurate age estimates for events back to the formation of Earth more than 4. Historians love to quote the dates of famous events in human history. They recount days of national loss and tragedy like December 7, and September 11, And they remember birthdays: July 4, and, of course, February 12, the coincident birthdays of Charles Darwin and Abraham Lincoln. We trust the validity of these historic moments because of the unbroken written and oral record that links us to the not-so-distant past. But how can we be sure of those age estimates?
How Science Figured Out the Age of Earth
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:.
The half-life is for the parent isotope and so includes both decays.
Radiometric dating is the process of determining the age of rocks from the decay of their Potassium is an abundant element in the Earth’s crust. One isotope The uranium-lead method is the longest-used dating method. It was first used in.
Earth’s magnetic field periodically reverses such that the north magnetic pole becomes the south magnetic pole. The latest reversal is called by geologists the Matuyama-Brunhes boundary MBB , and occurred approximately , years ago. The MBB is extremely important for calibrating the ages of rocks and the timing of events that occurred in the geological past; however, the exact age of this event has been imprecise because of uncertainties in the dating methods that have been used.
The team studied volcanic ash that was deposited immediately before the MBB. This volcanic ash contains small crystals called zircons. Some of these crystals formed at the same time as the ash; thus, radiometric dating of these zircons using the uranium-lead method provided the exact age of the ash. To verify their findings, the researchers also used a different method to date sedimentary rock from the same place that was formed at the time of the MBB. The combined results demonstrate that the age of the MBB is The research has been published in the journal Geology.
Yusuke Suganuma of the National Institute of Polar Research, Tokyo, who is the lead author on the paper, commented: “This study is the first direct comparison of radiometric dating, dating of sediments, and the geomagnetic reversal for the Matuyama-Brunhes boundary. Our work contributes calibrating the geological time scale, and will be extremely important in future studies of the events that occurred at this time.
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AGE OF THE EARTH
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.
By dating the rocks in Earth’s ever-changing crust, as well as the rocks measured ratios of lead isotopes in samples of the meteorite that put.
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.
When Galileo was led by his astronomical observations to “radical” ideas such as the Earth moving around the Sun, he was ordered to abandon his heliocentric ideas. This religiously-motivated ban on advocacy of heliocentrism lasted more than years. Ernst Mayr suggested that new discoveries such as recognition by astronomers of the large distance to the stars was important in allowing Europeans to begin to think about both vast space and long durations of time .
In response to astronomical observations made using telescopes, some philosophers such as Immanuel Kant , Universal Natural History and Theory of Heaven eventually began to discuss cosmological theories in which the universe might have “infinite extent, both in space and time”.
How is Earth’s Age Calculated?
Note: In this ongoing series, instead of summarizing a recent result from astro-ph, we will discuss a historical discovery from a paper that has become an astrophysical classic. Clair Patterson. It took homo sapiens hundreds of thousands of years on the planet to understand a fundamental, simple-sounding, question: how old is the Earth?
What is the role of geochronology in Earth and planetary sciences? Refinements in uranium-lead dating of zircon can date crystallization.
Football is fun for bickering, but for really wrecking family dinners over the Thanksgiving holidays, try tackling the week’s political argument over the age of the Earth. The fun kicked off when GQ Magazine quoted political hot property Sen. Marco Rubio, R-Fla. But Rubio’s answer upset pundits and geophysicists. The actual age of our planet had been provided some time ago by a scientist whose contributions were ignored in the opinion-page fights that followed.
The scientist was Caltech geophysicist, Clair Cameron Patterson , the forgotten man in the week’s most discussed debate, besides Thursday’s Lions vs. Texans NFL refereeing debacle , of course.
Clair Patterson’s Early Life and Research
When asked for your age, it’s likely you won’t slip with the exception of a recent birthday mistake. But for the sprawling sphere we call home, age is a much trickier matter. Before so-called radiometric dating, Earth’s age was anybody’s guess. Our planet was pegged at a youthful few thousand years old by Bible readers by counting all the “begats” since Adam as late as the end of the 19th century, with physicist Lord Kelvin providing another nascent estimate of million years.
Kelvin defended this calculation throughout his life, even disputing Darwin’s explanations of evolution as impossible in that time period.
Earth’s oldest asteroid impact may have helped lift the planet out of a deep freeze The geologists who reported the date last week, here at the Goldschmidt of radioactive uranium, trapped within the crystal, decay into lead.
Clair Patterson, an American geochemist, was born June 2, Patterson is one of the most unsung of the great 20th-century geologists. His specialty was geochronology—the dating of the Earth. Ever since , when radiometric dating was first proposed, the basic technique for dating the Earth had been the same: compare the amount of uranium in a rock with the amount of its radioactive decay byproduct, a specific isotope of lead. The more lead and the less uranium , the older the rock.
But this was a difficult series of measurements, complicated by the fact that one had to estimate how much lead was in the rock to start with primordial lead. By , Holmes had pushed the age back to about 3. Since it was pretty well acknowledged that the oldest rocks on Earth were younger than the Earth itself the Earth having been molten in its early days , Patterson turned to meteorites, judging that the oldest meteorites and the Earth formed at about the same time.
It is an accurate way to date specific geologic events. This is an enormous branch of geochemistry called Geochronology. There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate. As one example, the first minerals to crystallize condense from the hot cloud of gasses that surrounded the Sun as it first became a star have been dated to plus or minus 2 million years!!
That is pretty accurate!!! Other events on earth can be dated equally well given the right minerals.
The main problem with using this method of dating was that Patterson needed lead- and uranium-bearing crystals would have had to be as old as the Earth.
The discovery of the radioactive properties of uranium in by Henri Becquerel subsequently revolutionized the way scientists measured the age of artifacts and supported the theory that the earth was considerably older than what some scientists believed. There are several methods of determining the actual or relative age of the earth’s crust: examination of fossil remains of plants and animals, relating the magnetic field of ancient days to the current magnetic field of the earth, and examination of artifacts from past civilizations.
However, one of the most widely used and accepted method is radioactive dating. All radioactive dating is based on the fact that a radioactive substance, through its characteristic disintegration, eventually transmutes into a stable nuclide. When the rate of decay of a radioactive substance is known, the age of a specimen can be determined from the relative proportions of the remaining radioactive material and the product of its decay. In , the American chemist Bertram Boltwood demonstrated that he could determine the age of a rock containing uranium and thereby proved to the scientific community that radioactive dating was a reliable method.
Uranium, whose half-life is 4. Boltwood explained that by studying a rock containing uranium, one can determine the age of the rock by measuring the remaining amount of uranium and the relative amount of lead The more lead the rock contains, the older it is.
How Old is Earth, and How Do We Know?
Science in Christian Perspective. Radiometric Dating. A Christian Perspective. Roger C. Wiens has a PhD in Physics, with a minor in Geology.
Harold Jeffreys1 suggests two statistical methods for estimating t0, the age of the earth’s crust, from the data on tha isotopic constitution of ore-leads of different.
To support our nonprofit science journalism, please make a tax-deductible gift today. Geochronologists have tried to pinpoint the age of the million-year-old Deccan Traps, massive lava flows in India that may have helped wipe out the dinosaurs. But for too long, the arbiters of these stories—the geochronologists who date the age of rocks—have been underfunded and uncoordinated.
It could also calibrate, standardize, and improve the efficiency of different methods, which are based on the radioactive decay of elements within a rock. The consortium could help geochronology emerge from a deep slump, says Mark Harrison, a geochemist at the University of California UC , Los Angeles, who led a proposal cited in the new report.
Ever since the U. The geochronology funding could also help iron out discrepancies between labs and dating systems, says Dennis Kent, a paleogeographer at Rutgers University, New Brunswick, and study co-author. Researchers want an anvil, similar to ones in Europe and Asia, that can work on larger, multimillimeter-size samples so they can perform a wider variety of measurements.
Finally, the agency should create a Near-Surface Geophysics Center, the report recommends. Many emerging tools, such as using nuclear magnetic resonance to study ground porosity, show potential but need further development. It did, however, recommend the continued development of several ambitious proposals that would require significant new investment from NSF, beyond the reach of the EAR budget.