Category Archives: Geology

Answer: Lord Kelvin, The Age of the Earth, and the Age of the Sun

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Yeshu Kolodni and Lord Kelvin

The question

In 1862, the physicist William Thomson (who later became Lord Kelvin) of Glasgow published calculations that fixed the age of Earth at between 20 million and 400 million years. Later in the 1890s Kelvin calculated the age of Earth by using thermal gradients, and arrived at an estimate of 100 million years old which he later reduced to 20 million years. (For much more interesting details see this Wikipedia article.)

The question was: what was the main reason for Lord Kelvin’s wrong estimation

a) Radioactivity – Heat produced by radioactive decay; this was a process unknown to science for decades to come.

b) Convection – The transfer of heat not through radiation or heat-conduction but through the movement of hot parts to the surface; this is a process familiar in home cooking.

Here is the answer and some discussion mainly based on what Yeshu Kolodny have told me.

The short answer: Continue reading

Test your Intuition/Knowledge: What was Lord Kelvin’s Main Mistake?

The_Earth_seen_from_Apollo_17

The age of the earth

(Thanks to Yeshu Kolodny) We now know that the age of the earth is 4.54±1% Billion years.

From Wikipedea: In 1862, the physicist William Thomson (who later became Lord Kelvin) of Glasgow published calculations that fixed the age of Earth at between 20 million and 400 million years. 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 convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface.

Test your intuition/knowledge

What was the main reason for Lord Kelvin’s wrong estimation

a) Radioactivity – Heat produced by radioactive decay; this was a process unknown to science for decades to come.

b) Convection – The transfer of heat not through radiation or heat-conduction but through the movement of hot parts to the surface; this is a process familiar in home cooking.

Continue reading