beoba

If we'd had an impact that strong that recently, I doubt there would be any humans around to talk about it. Also, such an impact wouldn't, I believe, cause the earth to go off axis and then return so quickly.

On another note, wouldn't such an impact be noticed in other records? The Chinese had been maintaining extensive astronomical records, including reports of the supernova that created the Crab Nebula, and they dont mention anything like this.

excreationist

from snopes:
"...Regardless of the amount of time involved, the discovery of a "missing" period of time remains implausible. If the sun had indeed stood still for a day a few millennia ago, we would have no way of determining that fact through astronomic observations today. We have no frame of reference, no "cosmic calendar" or "master clock" to check against to see if we're overdrawn at the Bank of Time. The concept described here would be like giving someone a non-functioning clock and asking him to determine how much time had elapsed since the clock had stopped running. One could note the positions of the hands on the dial and make a reasonable guess about what the time of day was when the clock stopped running, but without knowing whether that time was A.M. or P.M., and without knowing the calendar date on which stoppage occurred, one could not possibly make any reasonable estimate about how long ago the clock stopped...."

Arrowman said this earlier:
Basically this is different to what snopes is saying... George Dodwell is claiming to know astronomical information before and after the event. His "mathematical proof" is probably some equations that work out how much the earth would need to tilt for those Biblical things to happen and maybe how big the asteroid would be to.

scigirl

I think this fits better in Science and Skepticism...

scigirl

The Lone Ranger

KeithHarwood got it right.

An asteroid impact capable of causing a significant change in the Earth's axial tilt in only a day or so would have melted much or all of the Earth's surface, boiled away the oceans, etc.

Besides, if such a thing had happened in the past few thousand years, there would probably still be enough debris in orbit to give the Earth a neat ring system like Saturn's.

Cheers,

Michael

beoba

And we'd still have detectable residual shockwaves going through the Earth.

Skydancer

Not after this long. Still would be volcanism at the impact site, though.

What I find most amusing is when these folks propose an impact to explain a long day or other miracle tale - and then assume that the Earth would then return to its previous rotation without a second impact. They seem to think the Earth is on a string or something. No grasp of Newton's Laws.

Asha'man

Yep, this is the kicker. To stop the earth from rotating, you need to hit it with a plant-killer. To start it rotating again, you need a second hit, with exactly the same energy transfer as the first. What are the odds of two planet-killing asteroids hitting about a day apart, with the same energy transfer, but perfectly opposite angular momentum transfer?

Arrowman

Thanks for the input.

To be clear (and fair) - I don't think Helen was referring to the "Joshua's Missing Day" story so much as some other "weird movement of shadows" things that apparently happened in the Bible. I don't think she was claiming that the earth stopped so much as changed its tilt with the effect that (as we see in extreme latitudes) the sun "didn't go down" for a period. But to notion of the axis tilting enough that the sun would not go down in the Middle East is - er, is "ludicrous" too strong a word?

The one slightly plausible thing about this story is that Dodwell was not, I think, claiming to "now astronomical information before and after the event" which is what you would need for the "Missing Day" - but that ancient records of sun movement etc showed a discrepancy which could only be explained by a change in the tilt of the axis. Which is in itself just vaguely plausible - provided the ancient records were accurate to the degree required. Of course, Dodwell (according to Setterfield) felt he was able to rely on these records because 'the records were part of their religious practices so you would expect them to take great care with them'.

And then, as others have pointed out, you can't have an asteroid strike the planet without doing just a little collateral damage of which there might be a record, any more than you can have a suddent global flood without boiling a lot of fish.

Anyway - dissecting this lunacy is like nailing jelly to a wall. Maybe one day I'll dig into Dodwell a bit and find out exactly what he was on about. Apparently Setterfield is in no hurry to publish his papers, even though that was apparently his responsibility.

It just boils down (for me) to one question, which I think has already been answered - and forgive my ignorance - is there any evidence that the tilt of the earth's axis has changed at all, no matter how slightly, at any time in the past, for whatever reason? I'm hearing "no". I guess I'm thinking of the variations in magnetic field.

Tim Thompson

Dodwell's hypothesis is described in "<a href="http://www.creationism.org/ackerman/AckermanYoungWorldChap11.htm" target="_blank">The Top That Reeled</a>", chapter 11 of the online creationist book "<a href="http://www.creationism.org/ackerman/index.htm" target="_blank">It's a Young World After All</a>" (Paul Ackerman, 1986; "Exciting Evidences for Recent Creation").

What it all boils down to is that ancient science types measured the lengths of shadows of sticks, at solstice, for various reasons. This is, for instance, how <a href="http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Eratosthenes.html" target="_blank">Eratosthenes</a> measured the circumference of Earth (circa 200 BC). Needless to say, there are various levels of error, inaccuracy, or imprecision in the various measurements. Dodwell did something typical of the neo-Velikovskian types. He assumed that the ancients could not have made such mistakes, so the real truth must lie elsewhere. He assumed that the variations must be real, and represent a real shift in the position of the rotation axis of Earth relative to the sun. As seen by an observer on Earth, the same effect could be produced by changing the orientation of the fixed Earth to its axis, while the axis remains fixed relative to the sun. Dodwell does not consider this, but it may be an important omission.

Of course the basis of Dodwell's idea is "soft" to say the least, as it relies on the primary assumption that the ancient folks don't make mistakes. There are huge problems involved with shifting the rotation axis of Earth. A collision certainly could do it, but we know that most of the energy in any collision goes into vaporizing everything at the point of impact. By the time you are able to produce enough energy to significantly alter Earth's axial orientation, there should be a really big impact feature laying around somewhere (like a crater at least the size of Rhode Island), and various other evidence of a local big bang. And note that Dodwell says it all happened in or about 2345 BC , which is not all that long ago, geologically speaking. A really big impact crater produced that recently isn't going to erode away that quickly.

It's an unimpressive idea.

Now, as for the spin axis of Earth, there is no observational evidence that it has "suddenly" altered in any geologically recent epoch. However, the 26000 year <a href="http://www-istp.gsfc.nasa.gov/stargaze/Sprecess.htm" target="_blank">precession of the equinoxes</a> is a relatively smooth & orderly motion of the spin axis, caused mostly by lunar torque. That motion is tied into possible climate variations through <a href="http://www.ldeo.columbia.edu/~polsen/nbcp/cmintro.html" target="_blank">Milankovitch Theory</a>. Whether or not the Milankovitch signal is real remains controversial, but it does imply an absence of anything "sudden".

But there is another kind of motion, where the spin axis of Earth remains fixed relative to the "fixed stars", while the globular Earth "slips" relative to the axis. That phenomenon is called true polar wander. The <a href="http://scienceworld.wolfram.com/astronomy/ChandlerWobble.html" target="_blank">Chandler Wobble</a> is an example of true polar wander. In 1997 a team of scientists from <a href="http://www.caltech.edu/" target="_blank">Caltech</a> made news by claiming that evidence supported the hypothesis that a major episode of polar wander in the precambrian was one of the factors leading to the "Cambrian explosion" (<a href="http://pr.caltech.edu/media/lead/072497JLK.html" target="_blank">Scientists discover that "evolutionary big bang" may have been caused by Earth losing its balance half a billion years ago</a>).

Polar wander is a lot easier to pull off than a true reorientation of the spin axis, because it does not require the kind of huge torque needed to shift the angular momentum vector of the planet (which remains fixed). So even if Dodwell is right in his interpretation of ancient stick shadows, it makes a lot more sense to blame the phenomenon on polar wander. That is not without its own set of problems, but it does avoid altogether the problem of hiding big impact features.

And finally, I note that the orientation of the spin axis of Earth is stabilized by the moon. In general, a planetary obliquity (the angle between the spin axis and orbital plane) is chaotic (<a href="http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Natur.361..608L&db_key=AST&h igh=3cf96e067113933" target="_blank">The chaotic obliquity of the planets</a>, J. Laskar & P. Robutel, Nature 361(6413) 608-612, February 1993; <a href="http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993Natur.361..615L&db_key=AST&h igh=3cf96e067113933" target="_blank">Stabilization of the earth's obliquity by the moon</a>, J. laskar, F. Joutel & P. Robutel, Nature 361(6413) 615-617, February 1993).

Arrowman

Tim: "Thank you" seems hardly adequate.

<img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />