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Our planet was pegged at a youthful few thousand years old by Bible readers (by counting all the "begats" since Adam) as late as the end of the 19th century, with physicist Lord Kelvin providing another nascent estimate of 100 million years.Kelvin defended this calculation throughout his life, even disputing Darwin's explanations of evolution as impossible in that time period.Of course, Kelvin formed his estimates of the age of the Sun without the knowledge of fusion as the true energy source of the Sun.Without this knowledge, he argued that, “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.” This last statement was prophetic.When asked for your age, it's likely you won't slip (with the exception of a recent birthday mistake).But for the sprawling sphere we call home, age is a much trickier matter.
The best estimate for Earth's age is based on radiometric dating of fragments from the Canyon Diablo iron meteorite.This estimate was actually reduced over his lifetime to between 20 Ma and 40 Ma and eventually to less than 10 Ma. Perry, in particular, a noted physicists and former assistant to Kelvin, showed that cooling calculations using different but equally likely assumptions and data resulted in ages for the Earth of as much as 29 Ga.Of course, later scientists, like John Perry and T. After this came to light, Kelvin admitted that he might just as well have set his original upper limit on the age of the Earth at 4,000 Ma instead of 400 Ma.There were indeed powerful and unknown sources of energy fueling the Sun’s energy output.The same is true of the basis of Kelvin’s estimate of the age of the Earth.
At first, the use of “key” diagnostic fossils was used to compare different areas of the geologic column.