THE AGE OF THE EARTH - CONTINUED

A geologist, James Hutton (1726 – 1797), stated that it is evident that some rocks were formed by sediments compressed in layers, other rocks were certainly formed by volcanic action and exposed rocks were worn down by the action of wind and water, and so on. He also pointed out that this process was slow and also assumed that this process had probably always been going on at the same slow rate and that the Earth must be much older that the 6 000 years or so postulated by previous claims. He published this in a book Theory of the Earth in 1785 and is commonly regarded as the "father of geology".




And then, in 1896, Antoine Henri Becquerel (1852 – 1908), discovered radio-activity! Physicists soon found that the heavy metals, uranium and thorium, gave off radiations and were giving off heat continually, because atoms were breaking down. Ernest Rutherford (1871 – 1937) showed in 1904 that particular varieties of atoms broke down at fixed rates and this led to the discovery that in any such a reaction, half of the atoms breaking down would do it in a certain time interval, say x years and half of what remained would break down in an additional x years, and so on, and that period is called the "half-life". It was also found that elements could consist of different isotopes, a term that means that the different forms still had the same chemical features but that the atomic mass was different.



The first element found to be radio-active is uranium and it consists of two isotopes, namely uranium-238 (meaning an atomic mass of 238) and uranium-235 and the half-life of U-238 is 4 500 000 000 years and that of U-235 is 700 000 000 years. The second element found to be radioactive is thorium, which has only one form with a half-life of 13 500 000 000 years. In that same year of 1904, Bertram Borden Boltwood (1870 – 1927) discovered the fact that both uranium and thorium break down to final non-radio-active products, uranium-238 ended as lead-206, uranium-235 as lead-207 and thorium as lead-208, three of the four isotopes of lead. Boltwood also showed in 1907 that these facts could be used to calculate the age of rocks on earth by measuring how much lead of each isotope the rocks contained and today scientists agree that the age of the earth is of the order of 4 500 000 000 years.



Quite a bit older than I am!



Oupa