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How We Know the Age of the Earth
 

How We Know the Age of the Earth

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  • <br />
  • kelvin &#x2013; a (thermodynamic) revolution against a (geological) revolution that would require another (radioactive) revolution to get the right answer. <br /> <br />
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  • up to 1900 <br />
  • 1650 <br />
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  • published after death / slow development by natural processes (Neptunian) <br />
  • 1715 - long-term data was required / collected &#x201C;for the benefit of future ages.&#x201D; <br /> <br /> <br />
  • 1909: 150 million years. / Invented radium treatment (&#x201C;The Dublin Cure&#x201D;) for cancer <br /> <br />
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  • 35 of 50 volumes with supplements, one of which (1778) discussed geological history <br /> <br />
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  • Privately believed 3 billion years. <br />
  • Attended Glasgow University at age of 10 to study mathematics and then went to Cambridge. Upon retirement had over 600 articles and 70 patents. <br /> <br /> <br /> <br />
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  • Ironically, the only one of these assumptions that actually holds is the second one! <br /> <br />
  • But &#x2026; 98 million years is most likely. <br />
  • Developed equations for determining humane hangings. / Opposed Darwin &#x2013; so not doing this to help <br /> <br />
  • Died here in Phoenix of TB <br />
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  • president of the Geological Society, 1869. Points out the uncertainty in both assumptions and data. <br /> <br />
  • Columbia geologist / Elegant models are only as good at the premises and data that are entered into them. / The engineers who say that bees cannot fly. <br /> <br />
  • Becquerel had discovered radioactivity three years earlier &#x2013; much was to be discovered <br /> TC for the win! <br /> <br />
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  • 35 year old, giving talk in London. Kelvin was in the audience <br /> <br />
  • importance of convection and radiation (in crust & core) <br /> <br />
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  • This is a statistical claim about any given atom in a sample. Given the large number of atoms in even a small sample, the claim hold nicely / decay constant is probability of given atom decaying per unit time / Soddy & Rutherford 1902 <br /> <br /> <br /> <br />
  • This is a statistical claim about any given atom in a sample. Given the large number of atoms in even a small sample, the claim hold nicely / decay constant is probability of given atom decaying per unit time / Soddy & Rutherford 1902 <br /> <br /> <br /> <br />
  • Only a single variation in decay rate has been reproduced (that of 7Be) and that was a variation of only 0.18%, not enough to alter any clock (if there was one using 7Be) <br />
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  • &#x201C;One of the greatest pieces of geological literature ever published.&#x201D; (Peter Wyse Jackson, 2007 <br />
  • How do you test this assumption of a closed system? You don&#x2019;t just take a rock, any rock, measure some stuff, and come up with an age. <br /> <br />
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  • Meteor Crater / 50,000 years ago / 45 m wide rock weighing 300,000 tons moving at ~30,000 mph. / Impact ~ 2.5 megatonnes TNT (i.e. 150x Hiroshima) / 175 million tons of rock were moved and scattered over 100 sq miles. Everything up to 10 miles away was flattened. / 5.5 scale earthquake was produced. <br /> <br />
  • Meteor Crater / 50,000 years ago / 45 m wide rock weighing 300,000 tons moving at ~30,000 mph. / Impact ~ 2.5 megatonnes TNT (i.e. 150x Hiroshima) / 175 million tons of rock were moved and scattered over 100 sq miles. Everything up to 10 miles away was flattened. / 5.5 scale earthquake was produced. <br /> <br />
  • Meteor Crater / 50,000 years ago / 45 m wide rock weighing 300,000 tons moving at ~30,000 mph. / Impact ~ 2.5 megatonnes TNT (i.e. 150x Hiroshima) / 175 million tons of rock were moved and scattered over 100 sq miles. Everything up to 10 miles away was flattened. / 5.5 scale earthquake was produced. <br /> <br />
  • Meteor Crater / 50,000 years ago / 45 m wide rock weighing 300,000 tons moving at ~30,000 mph. / Impact ~ 2.5 megatonnes TNT (i.e. 150x Hiroshima) / 175 million tons of rock were moved and scattered over 100 sq miles. Everything up to 10 miles away was flattened. / 5.5 scale earthquake was produced. <br /> <br />
  • Meteor Crater / 50,000 years ago / 45 m wide rock weighing 300,000 tons moving at ~30,000 mph. / Impact ~ 2.5 megatonnes TNT (i.e. 150x Hiroshima) / 175 million tons of rock were moved and scattered over 100 sq miles. Everything up to 10 miles away was flattened. / 5.5 scale earthquake was produced. <br /> <br />
  • Later became a pioneer of studying lead contamination <br />
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  • 1895 / 1900 / 1900 <br />
  • 1895 / 1900 / 1900 <br />
  • 1895 / 1900 / 1900 <br />
  • 1895 / 1900 / 1900 <br />

How We Know the Age of the Earth How We Know the Age of the Earth Presentation Transcript

  • It’s An Old Earth After All how geologists used physics to show the physicists that they were wrong
  • Methodologies Biblical Cooling of the Earth (Thermodynamic) Ocean chemistry Erosion and sedimentation
  • 4004 BCE
  • Benoît de Maillet 1656 - 1738 Telliamed, 1748 “Let us not measure the past duration of the world by that of our own years.” Used decline in sea level to obtain an age of two billion years.
  • “chiefly intended to refute the ancient notion, some have of late entertained, of the eternity of all things; though perhaps by it the world may be found much older than many have hitherto imagined.”
  • John Joly 1857 - 1933 “The quantity of sodium now in the sea, and the annual rate of its supply by the rivers, lead, it will be seen, to the deduction that the age of the Earth is 99 million years.” (1899)
  • Modern Salt “Clocks” < 100 years: Al < 1,000 years: Cr, Th, Ti, Fe < 10,000 years: Ni, Si, Pb, Mn < 100,000 years: Sn, Ba, Cu, Bi, Hg, Co < 1,000,000 years: Au, Mo, Sb, Rb, Zn < 10,000,000 years: Ag < 100,000,000 years: Na, Mg, Li, Sr, K
  • Problems Assumption of constant rate of influx across geologic time known to be wrong. Poorly estimated parameters: rates of erosion and solution, rainfall, runoff, continental area, average exposed rock composition over time. Ignores movement of elements out of oceans, movement which occurs at approximately the same rate as influx. Therefore confuses residence time with accumulation time.
  • Buffon
  • Epochs of Nature Formation of molten Earth Cooling to hand-hot temperature Enveloped with global sea Volcanic activity Emergence of land animals Tectonic activity forms the land masses Appearance of humans
  • Age of the Earth First application of experiment to problems of geology Cooling of metal spheres of various diameters Estimated 96,670 years for Earth to cool to current temperature.
  • William Thomson Lord Kelvin, 1824 - 1907 Professor of Natural Philosophy at Glasgow (1846 - 1899) Kelvin scale (1848) Second Law of Thermodynamics (1851) First transatlantic cable (1866) Peerage (1882) President, Royal Society (1890 – ‘95 )
  • Kelvin’s Cooling Argument All energy transformations result in loss of energy as heat (1852) “Within a finite period of time the Earth must have been, and within a finite period of time to come the Earth must again be, unfit for the habitation of man as at present constituted, unless operations have been, or are to be performed, which are impossible under the laws to which the known operations going on at present in the material world are subject.”
  • 1862 “It seems, therefore, on the whole most probable that the sun has not illuminated the earth for 100,000,000 years, and almost certain that he has not done so for 500,000,000 years. As for the future, we may say, with equal certainty, that inhabitants of the earth cannot continue to enjoy the light and heat essential to their life, for many million years longer, unless sources now unknown to us are prepared in the great storehouse of creation.”
  • 1864 “For eighteen years it has pressed on my mind, that essential principles of Thermo-dynamics have been overlooked by those geologists who uncompromisingly oppose all paroxysmal hypotheses, and maintain not only that we have examples now before us, on the earth, of all the different actions by which its crust has been modified in geological history, but that these actions have never, or have not on the whole, been more violent in past time than they are at present.”
  • Assumption: The earth is a warm, chemically inert planet that is cooling. Assumption: It can be modeled as an infinite plane of infinite thickness. Assumption: Heat loss is through conduction from the center.
  • Kelvin’s Estimate “I think we may with much probability say that the consolidation cannot have taken place less than 20,000,000 years ago, or we should have more underground heat than we actually have, nor more than 400,000,000 years ago, or we should not have so much as the least observed underground increment of temperature.”
  • Samuel Haughton 1821 - 1897 Applies Kelvin’s methodology and got an answer of 2.298 billion years.
  • Clarence King 1842 - 1901 First director of the US Geological Survey (1879 – ’81). 24 million years (1893)
  • Kelvin’s curve King’s curve Parameters: T: Initial temperature g: Thermogradient t: Cooling time
  • Kelvin 1897 “During the thirty-five years which have passed since I gave this wide-ranging estimate [20,000,000 – 400,000,000 years] experimental investigation has supplied much of the knowledge then wanting regarding the thermal properties of rocks to form a closer estimate of the time which has passed since the consolidation of the earth, and we have now good reason for judging that it was more than 20 and less than 40 million years ago, and probably much nearer 20 than 40 … I am not led to differ much from [King’s] estimate of 24,000,000 years.”
  • By 1900 Physicists seemed to be limiting the age of the Earth to around 25 million years. For biologists, this wasn’t a problem as they generally didn’t subscribe to an evolutionary process that required long periods of time and instead allowed for directed evolution. This was, however, a problem for the geologists who felt that long periods of time were needed for formation of the Earth as we see it today.
  • Thomas Henry Huxley “The argument is simple enough. Assuming the earth to be nothing but a cooling mass, the quantity of heat lost per year, supposing the rate of cooling to have been uniform, multiplied by any given number of years, will be given the minimum temperature that number of years ago. But is the earth nothing but a cooling mass… and has its cooling been uniform? … I do not think it can be denied that such conditions may exist, and may so greatly affect the supply, and the loss, of terrestrial heat as to destroy the value of any calculations which leave them out of sight. ”
  • T.C. Chamberlain 1899 “The fascinating impressiveness of rigorous mathematical analyses, within its atmosphere of precision and elegance, should not blind us to the defects of the premises that condition the whole process. There is perhaps no beguilement more insidious and dangerous than an elaborate and elegant mathematical process built upon unfortified premises.”
  • T.C. Chamberlain 1899 “What the internal constitution of the atoms may be is yet an open question. It is not improbable that they are complex organizations and the seats of enormous energies.”
  • Rutherford & Soddy 1903 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 are considered to be available, i.e., if processes of sub-atomic change are going on.”
  • Ernest Rutherford 1904 “I saw [Kelvin] sit up, open an eye and cock a baleful glance at me! Then a sudden inspiration came to me, and I said Lord Kelvin had limited the age of the Earth, provided no new source of heat was discovered. That prophetic utterance refers to what we are considering tonight. Radium! Behold!”
  • John Joly 1857 - 1933
  • Problems with Kelvin’s Method Parameters are poorly known (conductivity of rocks; thermal gradient; initial temperature of the Earth; heat released upon crystallization; exact composition and structure of the Earth). Considers conduction but not convection. Ignores other sources of heat:
  • Sources of Heat Heat left over from the formation of the Earth, e.g. gravitational energy from compaction, mechanical energy from meteor impacts, chemical energy from the formation of the Fe-Ni core. Energy from contraction due to cooling Energy from ongoing core expansion Radioactivity
  • Daughter Parent
  • Constant Decay The radioactive decay rates of nuclides used in radiometric dating have not been observed to vary since their rates were directly measurable, at least within limits of accuracy. This is despite experiments that attempt to change decay rates. There is insufficient energy in geological processes to affect the decay rate. The half-lives of radioisotopes can be predicted from first principles through quantum mechanics. Any variation would have to come from changes to fundamental constants.
  • Ernest Rutherford 1906 “The helium observed in the radioactive minerals is almost certainly due to its production from the radium and other radioactive substances contained therein. If the rate of production of helium from known weights of the different radioelements were experimentally known, it should thus be possible to determine the interval required for the production of the amount of helium observed in radioactive minerals, or, in other words, to determine the age of the mineral.”
  • Arthur Holmes 1890 - 1965 “The association of lead with uranium in rock-minerals and its application to the measurement of geological time.” Transactions of the Royal Society (1911) Used U-Pb methods to date rocks from Ceylon to 1,640,000,000 years – the oldest rocks then known.
  • Assumptions
  • Sr87 + Sr86 Rb87 + Sr86
  • By 1950 The geologists had come to a lower limit for the age of the Earth of 3.35 billion years. The cosmologists however thought the universe was 1.80 billion years old. We have a problem. Who is right?
  • Modern Estimates Oldest metamorphic rocks: 3.85 billion years Age of crystallization of oldest mineral: 4.40 billion years
  • “Heavier-than-air flying machines are impossible.”
  • “Heavier-than-air “X-Rays are a hoax” flying machines are impossible.”
  • “Heavier-than-air “X-Rays are a hoax” flying machines are impossible.” “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement
  • “Heavier-than-air “X-Rays are a hoax” flying machines are impossible.” “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement