Earth as seen from Apollo 17

Modern geologists and geophysicists consider the age of the Earth to be around 4. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Geophysics, a major discipline of Earth sciences, is the study of the Earth by quantitative physical methods especially by seismic, electromagnetic 54 billion years (4. 54×10⁹ years). ^[1] This age has been determined by radiometric age dating of meteorite material^[2] and is consistent with the ages of the oldest-known terrestrial and lunar samples. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface

Historically, estimates of the age were based on either creation myths in religious texts, or philosophical interpretations of geologic features, most notably by the Greek philosophers Theophrastus and Xenophanes. A creation myth is a supernatural mytho-[[religion religious]] story or explanation that describes the beginnings of humanity, Earth, life, and The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language Theophrastus ( Greek:; 371 – c 287 BC a Greek native of Eressos in Lesbos, was the successor of Aristotle in the Peripatetic Xenophanes of Colophon ( Greek ( 570 – 480 BC was a Greek Philosopher, Poet, and social and religious Critic. Biblical young earth creationists believe that the earth was formed as recently as 4004 BC, whereas Hindu beliefs have the universe enduring for billions of years before being destroyed and recreated in an endless cycle. Etymology According to the Online Etymology Dictionary, the word bible is from Latin biblia, traced from the same word through Medieval Latin and Late Latin Young Earth creationism (YEC is the religious belief that Heaven, Earth, and Life on Earth were created by a direct act of God dating A Hindu ( Devanagari: हिन्दू is an adherent of the philosophies and scriptures of Hinduism, a set of religious, Philosophical The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy

Following the scientific revolution and the development of radiometric age dating, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The period which many historians of science call the Scientific Revolution can be roughly dated as having begun in 1543 the year in which Nicolaus Copernicus published A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific ^[3] The oldest such minerals analysed to date – small crystals of zircon from the Jack Hills of Western Australia – are at least 4. Zircon is a Mineral belonging to the group of nesosilicates. Its chemical name is Zirconium silicate and its corresponding chemical formula is The Jack Hills are located in the Narryer Gneiss Terrane of the Yilgarn Craton, Western Australia, and comprise an 80 km long northeast-trending belt of Western Australia is a state occupying the entire western third of the Australian continent. 404 billion years old. ^[4] Comparing the mass and luminosity of the Sun to the multitudes of other stars, it appears that the solar system cannot be much older than those rocks. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Luminosity has different meanings in several different fields of science The Sun (Sol is the Star at the center of the Solar System. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth Ca-Al-rich inclusions (inclusions rich in calcium and aluminium) – the oldest known solid constituents within meteorites that are formed within the solar system – are 4. A calcium-aluminium-rich inclusion or Ca-Al-rich inclusion (CAI is a Centimeter -sized light-colored Calcium - and Aluminium -rich inclusion Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 WikipediaNaming A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface 567 billion years old,^[5] giving an age for the solar system and an upper limit for the age of the Earth. It is hypothesised that the accretion of the Earth began soon after the formation of the Ca-Al-rich inclusions and the meteorites. In Astrophysics, the term accretion is used for at least two distinct processes Because the exact accretion time of the Earth is not yet known, and the predictions from different accretion models range from a few millions up to about 100 million years, the exact age of the Earth is difficult to determine. It is also difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages. The oldest rock or rocks on Earth, as an aggregate of Minerals that have not undergone subsequent metamorphosis, are from the Archean The Acasta Gneiss of Northern Canada may be the oldest known exposed crustal rock. The Acasta Gneiss is a rock Outcrop of Archaean Tonalite Gneiss in the Slave craton in Northwest Territories Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page ^[6]

Development of modern geologic concepts

Studies of strata, the layering of rock and earth, gave naturalists an appreciation that the Earth may have been through many changes during its existence. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes Natural history is the Scientific research of Plants or Animals leaning more towards the Observational than Experimental methods These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Xenophanes interpreted fossil-bearing strata in much the same way during the 6th Century BC. Xenophanes of Colophon ( Greek ( 570 – 480 BC was a Greek Philosopher, Poet, and social and religious Critic.

Nicolas Steno (17th Century) was one of the first Western naturalists to appreciate the connection between fossil remains and strata. Nicolas Steno ( Danish: Niels Stensen; Latinized to Nicolaus Stenonis) ( January 10, 1638 - November 25, His observations led him to formulate important stratigraphic concepts (i. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) e. , the "law of superposition" and the "principle of original horizontality"). The law of superposition (or the principle of superposition) is a key axiom based on observations of Natural history that is a foundational principle of sedimentary The Principle of Original Horizontality was proposed by the Danish geological pioneer Nicholas Steno (1638-1686 In the 1790s, the British naturalist William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age. William Smith ( March 23 1769 &ndash August 28 1839) was an English Geologist, credited with creating the first nationwide William Smith's nephew and student, John Phillips, later calculated by such means that the Earth was about 96 million years old. For other people with this name see John Phillips John Phillips FRS ( December 25, 1800 &ndash April

The naturalist Mikhail Lomonosov, regarded as the founder of Russian science, suggested in the mid-18th century that the Earth had been created separately from the rest of the universe, several hundred thousand years before. Mikhail Vasilyevich Lomonosov (Михаи́л Васи́льевич Ломоно́сов () was a Russian Polymath, scientist Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending Lomonosov's ideas were mostly speculative, but in 1779, the French naturalist the Comte du Buffon tried to obtain a value for the age of the Earth using an experiment: He created a small globe that resembled the Earth in composition and then measured its rate of cooling. This article is about the country For a topic outline on this subject see List of basic France topics. Georges-Louis Leclerc fr Comte de Buffon ( September 7, 1707 April 16, 1788) was a French naturalist, mathematician biologist This led him to estimate that the Earth was about 75,000 years old.

Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present In 1830, the geologist Charles Lyell, developing ideas found in Scottish natural philosopher James Hutton, popularized the concept that the features of the Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. Sir Charles Lyell 1st Baronet, KT, FRS (14 November 1797 &ndash 22 February 1875 was a Scottish Lawyer, Geologist, and protagonist James Hutton MD (3 June 1726 OS (14 June 1726 NS) Edinburgh 26 March 1797 was a Scottish Geologist, This was a challenge to the traditional view, which saw the history of the Earth as static, with changes brought about by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.

Early calculations: physicists, geologists and biologists

William Thomson, aka Lord Kelvin.

In 1862, the physicist William Thomson (who later became Lord Kelvin) of Glasgow published calculations that fixed the age of the Earth at between 24 million and 400 million years. William Thomson 1st Baron Kelvin (or Lord Kelvin) OM, GCVO, PC, PRS, FRSE, (26 June 1824 &ndash 17 December 1907 Glasgow (ˈglæzgoʊ is the largest city in Scotland and third most populous in the United Kingdom ^[7][8] He assumed that the Earth had been created as a completely molten ball of rock, and determined the amount of time it took for the ball to cool to its present temperature. His calculations did not account for the ongoing heat source in the form of radioactive decay, which was unknown at the time.

Geologists had trouble accepting such a short age for the Earth. Biologists could accept that the Earth might have a finite age, but even 100 million years seemed much too short to be plausible. Charles Darwin, who had studied Lyell's work, had proposed his theory of the evolution of organisms by natural selection, a process whose combination of random heritable variation and cumulative selection implies great expanses of time. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life eVolution is the third Album by eLDee, it was due to be released in 2008 Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of Even 400 million years did not seem long enough.

In a lecture in 1869, Darwin's great advocate, Thomas H. Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. Thomas Henry Huxley PC FRS (4 May 1825 – 29 June 1895 was an English Biologist, known as "Darwin's Bulldog" for his advocacy The German physicist Hermann von Helmholtz (in 1856) and the Canadian astronomer Simon Newcomb (in 1892) contributed their own calculations of 22 and 18 million years respectively to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born. Simon Newcomb ( March 12 1835 &ndash July 11 1909) was a Canadian American Astronomer and Mathematician ^[8] Their values were consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its gravitational contraction. Gravitational collapse in Astronomy is the inward fall of a massive body under the influence of the force of Gravity. The process of solar nuclear fusion was not yet known to science. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus

Other scientists backed up Thomson's figures as well. Charles Darwin's son, the astronomer George H. Darwin of the University of Cambridge, proposed that the Earth and Moon had broken apart in their early days when they were both molten. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life Sir George Howard Darwin, FRS ( July 9 1845 &ndash Cambridge, December 7 1912) was an English The University of Cambridge (often Cambridge University) located in Cambridge, England, is the second-oldest university in the He calculated the amount of time it would have taken for tidal friction to give the Earth its current 24-hour day. Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i His value of 56 million years added additional evidence that Thomson was on the right track. ^[8]

In 1899 and 1900, John Joly of the University of Dublin calculated the rate at which the oceans should have accumulated salt from erosion processes, and determined that the oceans were about 80 to 100 million years old. John Joly ( November 1 1857 &ndash December 8 1933) was an Irish scientist possibly most famous for his development of Radiotherapy The University of Dublin, corporately designated the Chancellor Doctors and Masters of the University of Dublin (since the 19th century located in Dublin, Halite is the Mineral form of Sodium chloride, Na[[chlorine Cl]] commonly known as rock salt. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind ^[8]

Radioactive dating

Main article: Radiometric dating

Overview

Rock minerals naturally contain certain elements and not others. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. By the process of radioactive decay of radioactive isotopes occurring in a rock, exotic elements can be introduced over time. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. 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 Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance Half-Life (computer-game page here It's already listed in the disambiguation page Typical radioactive end products are argon from potassium-40 and lead from uranium and thorium decay. This article pertains to the chemical element For other uses see Argon (disambiguation. Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 If the rock becomes molten, as happens in the Earth's mantle, such nonradioactive end products typically escape or are redistributed. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Thus the age of the oldest terrestrial rock gives a minimum for the age of the Earth assuming that a rock cannot have been in existence for longer than the Earth itself.

Convective mantle and radioactivity

In 1892, Thomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. William Thomson 1st Baron Kelvin (or Lord Kelvin) OM, GCVO, PC, PRS, FRSE, (26 June 1824 &ndash 17 December 1907 Kelvin calculated the age of the Earth by using thermal gradients, and arrived at an estimate of 100 million years old. Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter from a region of higher Temperature to a region of lower ^[9] He did not realize that Earth has a highly viscous fluid mantle, and this ruined his calculation. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided In 1895, John Perry produced an age of the Earth estimate of 2 to 3 billions years old using a model of a convective mantle and thin crust. John Perry (1850-1920 was a pioneering Engineer and Mathematician from Ireland. ^[9] Kelvin stuck by his estimate of 100 million years, and later reduced the estimate to about 20 million years.

Radioactivity would introduce another factor in the calculation. In 1896, the French chemist A. Henri Becquerel discovered radioactivity. Antoine Henri Becquerel (15 December 1852 &ndash 25 August 1908 was a French Physicist, Nobel laureate, and one of the discoverers of Radioactivity Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. In 1898, two other French researchers, Marie and Pierre Curie, discovered the radioactive elements polonium and radium. Pierre Curie (15 May 1859 &ndash 19 April 1906 was a French physicist, a pioneer in Crystallography, Magnetism, Piezoelectricity Polonium (pəˈloʊniəm is a Chemical element with the symbol Po and Atomic number 84 discovered in 1898 by Marie and Pierre Curie Radium (ˈreɪdiəm is a radioactive Chemical element which has the symbol Ra and Atomic number 88 In 1903 Pierre Curie and his associate Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour.

Geologists quickly realized that the discovery of radioactivity upset the assumptions on which most calculations of the age of the Earth were based. These calculations assumed that the Earth and Sun had been created at some time in the past and had been steadily cooling since that time. Radioactivity provided a process that generated heat. George Darwin and Joly were the first to point this out, also in 1903. ^[10]

Invention of radiometric dating

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 in 1908.

Ernest Rutherford and Frederick Soddy had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Frederick Soddy ( 2 September 1877 &ndash 22 September 1956) was an English radiochemist. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. They also determined that a particular 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". Half-Life (computer-game page here It's already listed in the disambiguation page

Some radioactive materials have short half-lives; some have long half-lives. Uranium, thorium, and radium have long half-lives, and so persist in the Earth's crust, but radioactive elements with short half-lives have generally disappeared. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 Radium (ˈreɪdiəm is a radioactive Chemical element which has the symbol Ra and Atomic number 88 This suggested that it might be possible to measure the age of the 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. A Stable element is a Chemical element with at least one naturally occurring Stable isotope. Such "decay series", 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 Bertram B. Boltwood, a young chemist just out of Yale, and the energetic Rutherford. Bertram Borden Boltwood ( July 27, 1870 Amherst Massachusetts - 1927 Hancock Point Maine) was an American pioneer of Radiochemistry Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in 1904^[11], Boltwood was inspired to describe the relationships between elements in various decay series. Late in 1904, 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. Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 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.

Soddy and Sir William Ramsay, then at University College in London, 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. Sir William Ramsay (2 October 1852 &ndash 23 July 1916 was a Scottish chemist who discovered the Noble gases and received the Nobel Prize in The term " university college " is used in a number of countries to denote institutions that provide Tertiary education but do not have full or independent He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote,

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!' Behold! the old boy beamed upon me. ^[12]

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 1905, he suggested that lead was the final stable product of the decay of radium. Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly 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 1905 had provided dates for 26 separate rock samples, ranging from 92 to 570 million years. 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 1907. ^[3]

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. However, 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 250 million to 1. 3 billion years.

Arthur Holmes establishes radiometric dating

Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity. Boltwood gave up work on radiometric dating and went on to investigate other decay series. Rutherford remained mildly curious about the issue of the age of the Earth but did little work on it.

Robert Strutt tinkered with Rutherford's helium method until 1910 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. Arthur Holmes ( January 14 1890 &ndash September 20 1965) was a British Geologist. Holmes focused on lead dating, because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in 1911 that the oldest (a sample from Ceylon) was about 1. 6 billion years old. ^[13] These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed.

More important, in 1913 research was published showing that elements generally exist in multiple variants with different masses, or "isotopes". Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "neutrons". This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. 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. Holmes felt that they gave him tools to improve his techniques, and he plodded ahead with his research, publishing before and after the First World War. His work was generally ignored until the 1920s, though in 1917 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 the Earth.

Holmes's persistence finally began to pay off in 1921, when the speakers at the yearly meeting of the British Association for the Advancement of Science came to a rough consensus that the 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 1927 in which he presented a range of 1. 6 to 3. 0 billion years. ^[14] 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. The growing weight of evidence finally tilted the balance in 1931, when the National Research Council of the US National Academy of Sciences finally decided to resolve the question of the age of the Earth by appointing a committee to investigate. The National Research Council (NRC of the USA is the working arm of the United States National Academy of Sciences and the United States National Academy of The National Academy of Sciences (NAS is a corporation in the United States whose members serve Pro bono as "advisers to the nation on science 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. ^[14]

The 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.

Modern radiometric dating

Radiometric dating continues to be the predominant way scientists date geologic timescales. Techniques for radioactive dating have been tested and fine tuned for the past 50+ years. Forty or so different dating techniques are utilized to date a wide variety of materials, and dates for the same sample using these 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. Hundreds to thousands of measurements are done daily with excellent precision and accurate results. Even so, research continues to refine and improve radiometric dating to this day.

Why meteorites were used

Today's accepted age of the Earth of 4. 55 billion years was determined by C.C. Patterson using uranium-lead isotope dating (specifically lead-lead dating) on several meteorites including the Canyon Diablo meteorite and published in 1956. Clair Cameron Patterson ( June 2, 1922 – December 5, 1995) was a Geochemist born in Mitchellville Iowa, United Lead-lead dating is a method for dating geological samples normally based on 'whole-rock' samples of material such as granite ^[2]

Lead isotope isochron diagram showing data used by Patterson to determine the age of the Earth in 1956.

The quoted age of the 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 the Earth are unable to give a direct date of the formation of the Earth from the solar nebula because the 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. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere. Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat

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. A nuclide (from lat nucleus is a species of Atom characterized by the constitution of its nucleus and hence by the number of Protons, the number of To mitigate this effect it is usual to date several minerals in the same sample, to provide an isochron. Isochron dating is a common technique of Radiometric dating and is applied to date certain events such as Crystallization Metamorphism, shock events and Alternately, 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. Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed. To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.

Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of the 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. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Galena is the natural mineral form of Lead sulfide. It is the most important Lead Ore mineral These have returned age dates of 4. 54 billion years with a precision of as little as 1% margin for error. ^[15]

Why the Canyon Diablo meteorite was used

Fragment of the Canyon Diablo iron meteorite.

The Canyon Diablo meteorite was used because it is a very large representative of a particularly rare type of meteorite which contains sulfide minerals (particularly troilite, FeS), metallic nickel-iron alloys, plus silicate minerals. The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation Pyrrhotite is an unusual Iron Sulfide mineral with a variable iron content Fe(1-xS (x = 0 to 0 Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26

Barringer Crater, Arizona where the Canyon Diablo meteorite was found. Meteor Crater is a Meteorite Impact crater located approximately 43 miles east of Flagstaff, near Winslow in the northern

This is important because the presence of the three mineral phases allows investigation of isotopic dates using samples which provide a great separation in concentrations between parent and daughter nuclides. This is particularly true of uranium and lead. Lead is strongly chalcophilic and is found in the sulfide at a much greater concentration than in the silicate, versus uranium. The Goldschmidt classification, developed by Victor Goldschmidt, is a geochemical classification which groups the Chemical elements according to their preferred Because of this segregation in the parent and daughter nuclides during the formation of the meteorite, this allowed a much more precise date of the formation of the solar disk and hence the planets than ever before.

The Canyon Diablo date has been backed up by hundreds of other dates, from both terrestrial samples and other meteorites. The meteorite samples, however, show a spread from 4. 53 to 4. 58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the Sun and the planets. This 50 million year time span allows for accretion of the planets from the original solar dust and meteorites.

The moon, as another extraterrestrial body which has not undergone plate tectonics and which has no atmosphere, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the moon have been dated at a maximum of around 4. 4 and 4. 5 billion years old. Martian meteorites which have landed upon the Earth, have also been dated to around 4. 5 billion years old by lead-lead dating. Lead-lead dating is a method for dating geological samples normally based on 'whole-rock' samples of material such as granite

Altogether the concordance of age dates of both the earliest terrestrial lead reservoirs and all other reservoirs within the solar system found to date are used to support the hypothesis that the Earth and the rest of the solar system formed at around 4. 53 to 4. 58 billion years ago.

Helioseismic verification

The radiometric date of meteorites can be verified with studies of the Sun. The Sun can be dated using "helioseismic" methods which strongly agree with the radiometric dates found for the oldest meteorites. Helioseismology is the study of the propagation of Pressure waves in the Sun. ^[16]

See also

• Age of the universe
• Geochronology
• History of Earth
• Oldest rock
• Radiometric dating
• Timetable of the Precambrian
• Natural history

References

• Carlson R. W. & Tera F. , 1998. Lead-Lead Constraints on the time scale of early planetary differentiation. Origin of Earth and Moon Conference, Lunar and Planetary Society. PDF abstract
• Powell, James Lawrence, 2001, Mysteries of Terra Firma: the Age and Evolution of the Earth, Simon & Schuster, ISBN 0-684-87282-X
• Terada, K & Sano Y. , 2001. In-situ ion microprobe U-Pb dating of phosphates in H-chondrites. in Proceedings of the 11th Annual W.M. Goldschmidt Conference, Lunar and Planetary Society. PDF abstract
• Valley, John W. , William H. Peck, Elizabeth M. King (1999) Zircons Are Forever, The Outcrop for 1999, University of Wisconsin-Madison Wgeology.wisc.edu – Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4. 4 Gyr ago Accessed Jan. 10, 2006
• Wilde S. A. , Valley J. W. , Peck W. H. and Graham C. M. (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4. 4 Gyr ago. Nature, v. 409, pp. 175–178.
• Wyche, S. , D. R. Nelson and A. Riganti (2004) 4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton, Australian Journal of Earth Sciences Volume 51 Zircon ages from W. Australia – Abstract Accessed Jan. 10, 2006

External links

• TalkOrigins.org
• Vectorsite.net – Initial version of this article was based on a public domain text by Greg Goebel
• USGS preface on the Age of the Earth
• NASA exposition on the age of Martian meteorites
• "Aging the Earth", BBC Radio 4 In Our Time series, 2003

Further reading

• Baadsgaard, H. ; Lerbekmo, J. F. ; Wijbrans, J. R. , 1993. Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian-Maastrichtian stage boundary?). Canadian Journal of Earth Sciences, v. 30, p. 769–775.
• Baadsgaard, H. and Lerbekmo, J. F. , 1988. A radiometric age for the Cretaceous-Tertiary boundary based on K-Ar, Rb-Sr, and U-Pb ages of bentonites from Alberta, Saskatchewan, and Montana. Canadian Journal of Earth Sciences, v. 25, p. 1088–1097.
• Eberth, D. A. and Braman, D. , 1990. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation (Campanian) near Muddy Lake, west-central Saskatchewan. Bulletin of Canadian Petroleum Geology, v. 38, no. 4, p. 387–406.
• Goodwin, M. B. and Deino, A. L. , 1989. The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana. Canadian Journal of Earth Sciences, v. 26, p. 1384–1391.
• Gradstein, F. M. ; Agterberg, F. P. ; Ogg, J. G. ; Hardenbol, J. ; van Veen, P. ; Thierry, J. and Zehui Huang. , 1995. A Triassic, Jurassic and Cretaceous time scale. IN: Bergren, W. A.  ; Kent, D. V. ; Aubry, M-P. and Hardenbol, J. (eds. ), Geochronology, Time Scales, and Global Stratigraphic Correlation. Society of Economic Paleontologists and Mineralogists, Special Publication No. 54, p. 95–126.
• Harland, W. B. , Cox, A. V. ; Llewellyn, P. G. ; Pickton, C. A. G. ; Smith, A. G. ; and Walters, R. , 1982. A Geologic Time Scale: 1982 edition. Cambridge University Press: Cambridge, 131p.
• Harland, W. B. ; Armstrong, R.L.; Cox, A. Richard Lee “Dick” Armstrong FRSC ( August 4, 1937 – August 9, 1991) was an American / Canadian scientist V. ; Craig, L. E. ; Smith, A. G. ; Smith, D. G. , 1990. A Geologic Time Scale, 1989 edition. Cambridge University Press: Cambridge, p. 1–263. ISBN 0-521-38765-5
• Harper, C. W. , Jr. , 1980. Relative age inference in paleontology. Lethaia, v. 13, p. 239–248.
• Lubenow, M. L. , 1992. Bones of Contention: A Creationist Assessment of Human Fossils. Baker Book House: Grand Rapids.
• Obradovich, J. D. , 1993. A Cretaceous time scale. IN: Caldwell, W. G. E. and Kauffman, E. G. (eds. ). Evolution of the Western Interior Basin. Geological Association of Canada, Special Paper 39, p. 379–396.
• Palmer, Allison R. (compiler), 1983. The Decade of North American Geology 1983 Geologic Time Scale. Geology, v. 11, p. 503–504. September 12, 2004. Events 1213 - Albigensian Crusade: Simon de Montfort 5th Earl of Leicester, defeats Peter II of Aragon at the "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again "