Radiometric dating and the age of the Earth



Age of the Earth

The age of the Earth is approximately 4. Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. Because the exact amount of time this accretion process took is not yet known, and the predictions from different accretion models range from a few million up to about million years, the exact age of 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. Studies of stratathe layering of rocks and earh, gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.

Nicolas Steno in the 17th century was one of the first naturalists to radioactive dating of the earth the connection between fossil remains and strata. In the midth century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the kf. Lomonosov's ideas were mostly speculative. In the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created radioaactive small globe that resembled Dafing in composition and then measured its rate of cooling.

This led him to estimate that Earth was about 75, years old. Other naturalists used these hypotheses to radioactiive a history of Earththough their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. This was a challenge to the traditional view, which saw the history of Earth as static, [ citation needed ] with changes brought about by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.

Inradiozctive physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and million years. His calculations did not account for heat produced via radioactive decay a process then unknown to science or, more significantly, convection inside the Earth, which allows more heat to escape from the interior to warm rocks radioactivve the surface.

Geologists such as Charles Lyell had trouble accepting such a short age for Earth. For biologists, even million years seemed much too short to be plausible. In Darwin's theory of evolutionthe process of random heritable variation with cumulative selection requires great durations of time. According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3. In a lecture inDarwin's great advocate, Thomas H. Huxleyattacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions.

The physicist Hermann von Helmholtz in and astronomer Simon Newcomb in contributed their own calculations of 22 and 18 million years respectively to the debate: However, they assumed that radioactiev Sun was only glowing from the heat of its gravitational contraction. The process of solar nuclear fusion was not radioactive dating of the earth known to science.

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. Darwinproposed that Earth and Moon had radioactive dating of the earth 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, inwas: By their chemical te, 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.

InThomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. Kelvin calculated the age of the Earth by using thermal gradientsand he arrived at an estimate of about million years. InJohn 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 inMarie and Pierre Curie discovered the radioactive elements polonium and radium in ; and inPierre Curie and Albert Laborde raioactive 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 interracial couples dating site a radioactive element decays into another element radioactive dating of the earth a distinctive rate.


Radiometric Dating