Dating o datingskaters com
(According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3.5 to 3.8 billion years ago, the amount of time which passed since the last universal ancestor of all living organisms as shown by geological dating.) 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.
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.
Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than the Earth itself.
His value of 56 million years added additional evidence that Thomson was on the right track.
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.
Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth.This was a challenge to the traditional view, which saw the history of Earth as static, He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface to cool to its present temperature.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 near the surface.However, they assumed that the Sun was only glowing from the heat of its gravitational contraction.The process of solar nuclear fusion was not yet known to science.Kelvin stuck by his estimate of 100 million years, and later reduced it to about 20 million years.The discovery of radioactivity introduced another factor in the calculation.material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.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.In 1892, 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 100 million years.