The growth of a corral fossil over 1 day

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This is from a website on the effect of the moon on life on earth:

"By counting the growth rings in 400-million-year-old coral fossils and in 3-billion-year-old stromatolites, geologists calculate that Earth was rotating four times faster when it formed than it is today".

They could see growth rings of one day, over a 400-million-year coral? How can they possibly see that?
 

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I imagine the growth rings they counted were annual ones that differed because of effects caused by the Earth rotating so much faster.

Of course, that's backed by the fact that we know the Earth's rotation is slowing at a very small rate, and extrapolating that back to near the Earth's birth gives a similar number.
 
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I imagine the growth rings they counted were annual ones that differed because of effects caused by the Earth rotating so much faster.
If the earth was rotating much faster around itself, but at the same rate around the sun, then why would annual growth rings say anything about the earth's rotation around itself?
 
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It appears that the difference in day night uptake of carbonates produces visible daily (diurnal/circadian) growth rings:

http://links.jstor.org/sici?sici=0022-3360(197405)48:3<553:GLOTOF>2.0.CO;2-V&size=LARGE&origin=JSTOR-enlargePage

http://freepages.genealogy.rootsweb.com/~springport/geology/coral_growth.html

Over the year the seasons complete a cycle which is also visible in the growth rings, thus it appears possible to estimate the number of days in a year here, many million years ago.

http://www.springerlink.com/content/ww68nw27711245km/

But this may likely be under the assumption that the radius of the Earth orbit is constant, which may have been modified by the sum of all forces in the solar system.
 
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