In John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity. Other scientists backed up Thomson's figures. Charles Darwin 's son, the astronomer George H.
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Darwin , proposed that Earth and Moon had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for tidal friction to give Earth its current hour day. His value of 56 million years added additional evidence that Thomson was on the right track. The last estimate Thomson gave, in , was: By their chemical nature, rock minerals contain certain elements and not others; but in rocks containing radioactive isotopes, the process of radioactive decay generates exotic elements over time.
By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated. In , Thomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. Kelvin calculated the age of the Earth by using thermal gradients , and he arrived at an estimate of about million years. In , John Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust.
The discovery of radioactivity introduced another factor in the calculation. After Henri Becquerel 's initial discovery in , Marie and Pierre Curie discovered the radioactive elements polonium and radium in ; and in , Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth.
These had assumed that the original heat of the Earth and Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished. George Darwin and John Joly were the first to point this out, in Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.
Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a " half-life ", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".
Some radioactive materials have short half-lives; some have long half-lives.
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Uranium and thorium have long half-lives, and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples.
In reality, radioactive elements do not always decay into nonradioactive "stable" elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a stable element. These " decay chains ", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity and provided a basis for constructing techniques of radiometric dating.
The pioneers of radioactivity were chemist Bertram B. Boltwood and the energetic Rutherford.
Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in ,  Boltwood was inspired to describe the relationships between elements in various decay series. Late in , Rutherford took the first step toward radiometric dating by suggesting that the alpha particles released by radioactive decay could be trapped in a rocky material as helium atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.
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- Age of the Earth - Wikipedia?
Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium. He dated a rock in his possession to an age of 40 million years by this technique.
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I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!
Rutherford assumed that the rate of decay of radium as determined by Ramsay and Soddy was accurate, and that helium did not escape from the sample over time. Rutherford's scheme was inaccurate, but it was a useful first step. Boltwood focused on the end products of decay series. In , he suggested that lead was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium. Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium-lead decay chain could be used to date rock samples.
Boltwood did the legwork, and by the end of had provided dates for 26 separate rock samples, ranging from 92 to million years.
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He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium. Boltwood refined his work and finally published the results in Boltwood's paper pointed out that samples taken from comparable layers of strata had similar lead-to-uranium ratios, and that samples from older layers had a higher proportion of lead, except where there was evidence that lead had leached out of the sample. His studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium.
However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of million to 2. Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity.
Rutherford remained mildly curious about the issue of the age of Earth but did little work on it. Robert Strutt tinkered with Rutherford's helium method until and then ceased.
However, Strutt's student Arthur Holmes became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating, because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in that the oldest a sample from Ceylon was about 1.
For example, he assumed that the samples had contained only uranium and no lead when they were formed. More important research was published in It showed that elements generally exist in multiple variants with different masses, or " isotopes ". In the s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as " neutrons ".
In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series. Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless. His work was generally ignored until the s, though in Joseph Barrell , a professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating.
Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of Earth. Holmes' persistence finally began to pay off in , when the speakers at the yearly meeting of the British Association for the Advancement of Science came to a rough consensus that Earth was a few billion years old, and that radiometric dating was credible.
Holmes published The Age of the Earth, an Introduction to Geological Ideas in in which he presented a range of 1.
No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far. Holmes, being one of the few people on Earth who was trained in radiometric dating techniques, was a committee member, and in fact wrote most of the final report.
Thus, Arthur Holmes' report concluded that radioactive dating was the only reliable means of pinning down geological time scales. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.
Radiometric dating continues to be the predominant way scientists date geologic timescales. Techniques for radioactive dating have been tested and fine-tuned on an ongoing basis since the s. Forty or so different dating techniques have been utilized to date, working on a wide variety of materials. Dates for the same sample using these different techniques are in very close agreement on the age of the material. Possible contamination problems do exist, but they have been studied and dealt with by careful investigation, leading to sample preparation procedures being minimized to limit the chance of contamination.
An age of 4. The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research. Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics , weathering and hydrothermal circulation.
All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide a species of atom characterised by the number of neutrons and protons an atom contains or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an isochron.
Alternatively, more than one dating system may be used on a sample to check the date. Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed. Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead-lead isotope systems on the planet.
He returns to his hospital bed, where he awakes from his vision with his fever broken and his health beginning to recover. He makes amends with Louis, but refuses to take him back. The play concludes in Prior and Louis are still separated, but Louis, along with Belize, remains close in order to support and care for Prior, and Hannah has found new perspective on her rigid beliefs, allowing her to accept her son as he is and forge a friendship with Prior.
Prior, Louis, Belize, and Hannah gather before the angel statue in Bethesda Fountain , discussing the fall of the Soviet Union and what the future holds. Prior talks of the legend of the Pool of Bethesda , where the sick were healed. Prior delivers the play's final lines directly to the audience, affirming his intentions to live on and telling them that "the Great Work" shall continue. The play is written for eight actors, each of whom plays two or more roles. Kushner's doubling, as indicated in the published script, requires several of the actors to play the opposite gender. The play's second part, Perestroika , was still being developed as Millennium Approaches was being performed.
It was performed several times as staged readings by both the Eureka Theatre during the world premiere of part one in , and the Mark Taper Forum in May In November it received its London debut in a National Theatre production on the Cottesloe stage, in repertory with a revival of Millennium Approaches , again directed by Declan Donnellan. Wolfe , with Millennium Approaches performed on May 4 and Perestroika joining it in repertory on November 23, closing December 4, Among the replacements during the run were F.
The published script indicates that Kushner made a few revisions to Perestroika in the following year. These changes officially completed the work in Johnson as Joe Pitt, Barbara E. Kushner made relatively minor revisions to Millennium Approaches and additional, more substantial revisions to Perestroika during a run at the Signature Theatre in , which were published in a complete edition.
In , a production of the two-part play was produced by Sydney-based theatre company, Belvoir. The production finished its season on July Asia premiered the play in its entirety in by the New Voice Company in the Philippines. This was followed by another production in November at the Singapore Airlines Theatre. An Italian adaptation of the play premiered in Modena in , in a production directed by Ferdinando Bruni and Elio De Capitani  which was awarded several national awards.
The production received critical praise and launched the new theater company. In September , a revival of the two plays were staged in Melbourne at fortyfivedownstairs for nearly a four-week run. Kushner prefers that the theatricality be transparent. In his notes about staging, he writes: This must be an actor-driven event. The choice to have "no blackouts" allows audiences to participate in the construction of a malleable theatrical world.
One of the many theatrical devices in Angels is that each of the eight main actors has one or several other minor roles in the play. For example, the actor playing the nurse, Emily, also plays the Angel, Sister Ella Chapter a real estate agent , and a homeless woman. This doubling and tripling of roles encourages the audience to consider the elasticity of, for example, gender and sexual identities.
In , HBO Films created a miniseries version of the play. Kushner adapted his original text for the screen, and Mike Nichols directed. HBO broadcast the film in various formats: The first three chapters were initially broadcast on December 7, to international acclaim, with the final three chapters following. Angels in America was the most watched made-for-cable movie in and won both the Golden Globe and Emmy for Best Miniseries.
Kushner made certain changes to his play especially Part Two, Perestroika for it to work on screen, but the HBO version is generally a faithful representation of Kushner's original work. Kushner has been quoted as saying that he knew Nichols was the right person to direct the movie when, at their first meeting, Nichols immediately said that he wanted actors to play multiple roles , as had been done in onstage productions.
The opera was based on both parts of the Angels in America fantasia, however the script was re-worked and condensed to fit both parts into a two and half hour show. I rather focus on the passionate relationships, on the highly dramatic suspense of the wonderful text, on the permanently uncertain state of the visions.
The text of Prior Walter's soliloquy from Scene 5 of Perestroika was set to music by Michael Shaieb for a festival celebrating Kushner's work at the Guthrie Theater. The work premiered at the Guthrie in April The play garnered much praise upon its release for its dialogue and exploration of social issues.
A decade after the play's premiere, Metro Weekly labeled it "one of the most important pieces of theater to come out of the late 20th century. By contrast, in an essay titled "Angles in America", Lee Siegel wrote in The New Republic , " Angels in America is a second-rate play written by a second-rate playwright who happens to be gay, and because he has written a play about being gay, and about AIDS, no one—and I mean no one—is going to call Angels in America the overwrought, coarse, posturing, formulaic mess that it is.
In response to the frank treatment of homosexuality and AIDS, and brief male nudity, the play quickly became subject to controversial reaction from conservative and religious groups, sometimes labelled as being part of the " culture war ". From Wikipedia, the free encyclopedia. For the miniseries, see Angels in America miniseries. Angels in America miniseries. Seattle Times , June 25, Act I, Scene 1". Angels In America , Revised and Completed ed.
The Complete Oral History". Archived from the original on June 10, Zachary Quinto flies high in perfect revival of Tony Kushner play". New York Daily News. Retrieved July 20, National Post , August 8, Accessed 11 October El Nuevo Dia in Spanish. Superior acting delivers brilliant and moving work". The New York Times. Angels in America on HBO: Retrieved December 6, Artists' Values and Public Funding for the Arts". Awards for Angels in America. Drama Desk Award for Outstanding Play.
Millennium Approaches Angels in America: Helpmann Award for Best Play. Laurence Olivier Award for Best Revival. Pulitzer Prize for Drama. A Parable Rabbit Hole August: Tony Award for Best Play. Tony Award for Best Revival of a Play. Retrieved from " https: