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I was reading many articles about estimates of the age of the Earth throughout the ages. I was dumbfounded when I read that Newton, arguably one of the greatest scientists ever to have ‘calculated’ the age of the earth, estimated that the Earth was created in 4000 BCE. Johannes Kepler arrived at a similar result. Which methods did these scientists use to arrive at such conclusions?

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    $\begingroup$ It's especially surprising that as the concept of deep time was well established since the antiques. Already Aristotle and Xenophanes understood that the Earth was very old. Scholars as Ibn Sīnā, al-Bīrūnī and Shen Kuo had developed the concept of superposition and stratigraphy. Without modern dating techniques they naturally couldn't come up with a number, only that the earth have to be older than the time scales we are acquainted with. Even Lord Kelvins scientific approach based on thermal gradients and heat flux underestimated the age of the Earth with a factor of ten. $\endgroup$ – Tactopoda May 8 '15 at 19:02
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    $\begingroup$ @Tobbe: You need to realize, though, that in those days openly contradicting religious dogma was a dangerous act. $\endgroup$ – jamesqf May 9 '15 at 1:31
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    $\begingroup$ Yes. That was challenge, and still is in many cases. $\endgroup$ – Tactopoda May 9 '15 at 9:24
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    $\begingroup$ Interesting question. I like this summary: aip.org/history/curie/age-of-earth.htm - it doesn't mention Aristotle, but geological understanding, leading to a modern-ish much older earth estimate didn't happen till the mid 1800s. Surprising to me that it was that late. Lord Kelvin's calculation was done in 1892, long after the geologists began to suspect the earth was significantly older than previously believed, but before any understanding of radioactive heat. His was off by a lot but Perry in 1895 was close. More here: en.wikipedia.org/wiki/Age_of_the_Earth $\endgroup$ – userLTK May 10 '15 at 0:34
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The estimates of Newton and Kepler, and the similar estimates of dozens of their contemporaries, were produced by treating the Bible as a historically accurate document and deriving a chronology from it. I think that a detailed explanation of their techniques would be off-topic for Earth Science, but the Wikipedia page on the Ussher Chronology (which provides probably the most famous biblically-based estimate of the Earth's age) goes into reasonable detail about the methods used for such calculations.

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  • $\begingroup$ I see now, for a second I thought that the men had used their own contributions that we know today in their estimates. So there was nothing scientific about their chronologies. $\endgroup$ – Lucian09474 May 8 '15 at 18:46
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    $\begingroup$ @Lucian09474 I think Buffon gave one of the first age estimate based on some scientific reasonning (he was way off but still) by measuring the cooling schedule of heated iron cannon balls and extrapolating to earth size. $\endgroup$ – plannapus May 8 '15 at 18:52
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    $\begingroup$ Buffon was 700 years after Ibn-Sinaa. The Book of Healing was a part of the The Canon of Medicine and it was widespread in Europe at that time. The idea of deep time, scientific reasoning and method was well known by educated people and others with some common sense but neglected due to dogmatic religious ideologies. $\endgroup$ – Tactopoda May 9 '15 at 15:59

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