What (if any) evidence exists that can show conclusively what Earth's rotational period was 50, 100, 250, 1000 million years ago?

A simple regress of tidal slowing provides historic indication of rotational period.

I doubt there is any more direct indication left in the strata if that's what you're asking.

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I have seen reported evidence showing that the Lunar cycle has undergone only a slow and gradual shift, as would be expected of 2 relatively stable masses. This evidence was tidal.

I seek day length evidence.

Stromatolite layers give indications on day length, I think.

Devonian corals analysis seemed to show 400 days per year, meaning the earth had slowed down, assuming that there was no mechanism for the earth orbit about the sun to be longer. Other studies have been done since.

Evidence of slowing in historical times involves the study of ancient eclipses--because of their rarity and narrow viewing regions, the only way certain cities could have reported an eclipse is if the eclipse was a few hours late, according to the backtracking of the eclipse record. The results fit the lunar slowing fairly well.

Of course, there's always some argument.

Big dinosaurs. Faster rotation in the past>lower effective g on the surface>big dinosaurs.

Thanks for replies I will follow up. Any links anyone?

As others have indicated, the physics of lunar recession are inseparable from a slowing rotation, while certain marine fossils definitely indicate a different period in the past relative to today. Unfortunately though, extrapolation beyond these fossils is difficult, because IIRC the change is not quite linear, being affected by things like land-sea area that have changed dramatically over time.

http://curious.astro.cornell.edu/que...php?number=700

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"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

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So as Moon recesses Earth slows. Interesting that Devonian shows 400 days per year then. You would expect less than 365

Why?

The difference between then and now would have been a small fraction of 1% of the net g-force. I don't think the dinosaurs would have noticed it.

You are getting a fraction upside down. Faster rotation in the past means more days per year, provided the length of the year is virtually unchanged.

That was a joke! A bad one obviously...

Correct. My bad. I have same problem with clocks going back.

Tidal rhythmites. See my Talk.Origins entry: The Recession of the Moon and the Age of the Earth-Moon System and scroll down about halfway to the section labeled "The Paleontological Evidence". You will find there a short review of the evidence with references. Also see Tidal Time: Ancient Tides Recorded in Indiana Rocks from the Indiana Geological Survey.

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The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

I have a problem here

http://igs.indiana.edu/Geology/ancie...idaltime02.cfm

Scroll to the image showing tidal rhythmites/histograms

The dominant (evening) and subordinate (morning) tides are indicated

However if you count along you will find that the second annotated dominant lands where a subordinate should be

Also 36 hours apparently produces 2 cm deposit. Thats a half a metre a month! See anything like that happening now?

And here

http://igs.indiana.edu/Geology/ancie...idaltime03.cfm

The histogram does not seem to relate to the photograph

On the histogram we see a fairly sinusoidal modulation of tides, but on the rock even the (it seems to me rather speculative) assignment of neap and spring tides do not follow any obvious period.

I have CnP the photo into Powerpoint where I enlarge and apply my own lines and scale

There are alternating thin dark bands and thicker lighter bands. To the right of the sample photo bands expand to 3 or 4 per cm. To the left there are 10 or 11. Visually the interpretation seems not to fit the evidence. Is FT really apropos here? In audio we use FT to resolve single frequencies from multiplexed frequencies. Rock evidence shows clear periods.

When I last looked over the literature a dozen years ago, there was evidence that the earth had sped up, too, so it is not inseparable.

Wait a minute, kinda like now!

Awfully funny, though - and you owe me another gut for the one I just busted. On second thought, keep it. I've got enough gut.

From Wiki: "Over millions of years, the rotation is significantly slowed by gravitational interactions with the Moon."

Following the tidal acceleration link there, we find the Earth's day will lengthen to about a month long in 4.5 Billion years. Similarly, we find evidence in tidal rhythmites (alternating layers of sand and silt laid down from large estuary tidal flows) that about 620 million years ago, Earth's day was 21.9+/-0.4 hrs long.

In my above two posts I questioned the interpretations of two evidential photographs. I would be very grateful if you could check out my objections. I am sure something can be gleaned from tidal rhythmites - the principle is simple and elegant. If you have good links to photographs of rhythmites and interpretation of said photographs this would be appreciated.

I have no photographs myself, but the evidence is sound, as such deposits are still being created today.

The graph and the photograph may or may not be of the same data, but that in no way invalidates using rhythmites.

Leap seconds added since 1972 = 24
Leap seconds subtracted since 1972 = 0


Source

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"They reasoned that an object situated at the center and related equally to the extremes in every direction can have no impulse to move in any specific direction. In fact, they compared the situation of such an object with that of a man violently but equally hungry and thirsty, standing at the same distance from food and drink and unable to decide in which direction to move." - Aristotle

Mentioning the dinosaurs was not as silly as you think... we are not so cleaver that we see all that is or has happened here. How many lunar months per year = 13. So looking at the age of Mozes and Mathusla---Hmmm... 900 divided by 13 = 70... At the time a grand old age. Now stop getting all angry about so little information. The above silly observation may not have any truth in it. But you can argue some place else.
The point I am making is this. Our history is so short that we are unable to record accurately the length of days just 1000 years ago. The length of Earths year is more difficult to define. We can however Analise what we see today and extrapolate results from information made available to us today. We know that any changes are gradual and stability is one of the reasons we have evolved to this point. We have had time. Tidal sediment does not answer your question as well as a clock. You have to work with the tools you have. The best you have is estimates. We know what is happening now and can make informed assumptions about the history of Earth. Our ability to measure the length of a year has sharpened somewhat.

The slowing down that took over a hundred years, lengthening the day about two milliseconds, and about half has been "undone" in five or six years. Since the day is still longer than the day of the definition, leap seconds are still necessary, just not as often. Should the speeding up continue, to where another millisecond drops off, we'll not need leap seconds at all. If it speeds up past that, we'd have to start subtracting leap seconds, but only then.

That wikipedia article refers to the causes of Earth's speeding up as unknown, however one cause which is known to have caused Earth's rotation to speed up was the Boxing day's Tsunami's Earthquake:

Source

Generally speaking the energy of Earth's rotation is reduced by the drag imposed on it by tidal forces as well as the oceans and the atmosphere (i.e. it slows down).

Random major-catastrophic events such as Earthquakes or meteorite impacts may contribute by either slowing or speeding the rotation.

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"They reasoned that an object situated at the center and related equally to the extremes in every direction can have no impulse to move in any specific direction. In fact, they compared the situation of such an object with that of a man violently but equally hungry and thirsty, standing at the same distance from food and drink and unable to decide in which direction to move." - Aristotle

Actually I took the joke another way. Being that the height and COM of the dinosaurs collectively had the earth slower via conservation of angular momentum! But of course my fraction was upside down too.

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You say the evidence is sound. Where can one review this evidence? Leaving the graphs aside let's look at this particular piece of evidence.

http://igs.indiana.edu/Geology/ancie...idaltime02.cfm

Flawed or what?

edit

I uploaded an attachment jpeg but cannot see it?

edit

Here is my debunking of at least one piece of rhythmite evidence. I uploaded to another forum no problem

http://goldismoney.info/forums/attac...8&d=1224854224

Attached Thumbnails

 

i thought that mass was related to gravity

if the earth was spinning faster in the past, there would have been more mass around the equator. The stronger angular momentum must have caused the Earth to assume a more pronounced oblate spheroid shape. I would assume that more mass around the equator would produce a stronger gravitational effect.

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-work in progress--

Please tell us why you think they're either "flawed," or "what?"

Thanks.

"Analyzed" how, Rodin? A mere picture with a few D's on it is not analysis, nor is it "debunking."

I would not assume. I would calculate.

Unfortunately I do not have the skill to do a rigorous integration of an oblate spheroid. However, my hunch is that for a slightly oblate planet, the gravity at a point on the equator is not much different from that at a point the same distance from the center of a perfect sphere of the same mass. Going from the pole to the equator should weaken the gravity by moving us farther from the center. I welcome any response from someone who knows the details of the integration needed to solve this one.

Don't forget the double whammy caused by the centrifugal effect. That further reduces the effective weight of an object on the equator.