Age of the Moon

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

User avatar
knight427
Worshipful Sycophant
Posts: 240
Joined: Mon May 14, 2007 6:45 pm UTC
Location: Wisconsin
Contact:

Age of the Moon

Postby knight427 » Tue Dec 07, 2010 2:35 am UTC

Sources commonly claim the moon is approximately 4.5 billion years old. The most widely accepted theory proposes that Mars-sized protoplanet collided with Earth.

Meanwhile there is scientific research suggesting the moon's orbit does not support this theory. Everyone knows that the moon is slowly receding from Earth. Many models have been made to trace the orbit back in time and they all seem to collapse at about 1 billion years.

Evolution of the Earth-Moon System

Or perhaps I am misreading that paper. Can anyone reconcile the two?
knight427

If you GIVE a zombie a fish, you will feed him for minute.
If you TEACH a zombie to fish, he will be munching on you for hours.

User avatar
Zamfir
I built a novelty castle, the irony was lost on some.
Posts: 7604
Joined: Wed Aug 27, 2008 2:43 pm UTC
Location: Nederland

Re: Age of the Moon

Postby Zamfir » Tue Dec 07, 2010 10:53 am UTC

The paper has one single graph with an evolution all the way back to the beginning, with a collapse at roughly 2 or 3 billion years ago. But the paper also says they have problems with the very long run because of "dissipation", and they say their model is not good enough to deal with with the very early phase of the moon. See it as a model that describe the dynamics on time scales of thousands or millions of years very well, and gives a rough picture for the long run that is at least in the ball park.

User avatar
knight427
Worshipful Sycophant
Posts: 240
Joined: Mon May 14, 2007 6:45 pm UTC
Location: Wisconsin
Contact:

Re: Age of the Moon

Postby knight427 » Tue Dec 07, 2010 3:13 pm UTC

I understand your point about the limits of modeling accuracy. For an easy example we can think of objects falling very close to the ground. The model required for their decent is very simple. But as height increases you eventually have to consider air resistance which was negligible at low heights. Then there is decreasing gravity with height and the Coriolis effect and more.

So in this case we have a model that considers enough detail to predict the lunar orbit for millions of years, but falls short of predicting it to the end by a factor of 4. So this model must be missing something that only becomes significant over a great deal of time or only was significant when the moon was closer to Earth. I guess I was hoping someone here would be versed enough in the topic to address the shortcomings of the model. Since this model has not changed the predominate 4.5 billion year old moon theory, then one would assume its limitations are known which would inspire a better model. I can't find more recent models, though this is obviously not my field of study.
knight427



If you GIVE a zombie a fish, you will feed him for minute.

If you TEACH a zombie to fish, he will be munching on you for hours.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26830
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

Re: Age of the Moon

Postby gmalivuk » Tue Dec 07, 2010 5:35 pm UTC

I didn't look at the paper, but didn't Zamfir say the graph in the article collapses 2-3 billion years ago, contrary to your claim in the OP of 1 billion years?

In any case, the moon's orbit is changing because of gravitational effects of the tidal bulge it causes in Earth's oceans. Which means the configuration of said oceans should have a nontrivial effect over these kinds of timescales. Is that taken into account in the linked article?
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
knight427
Worshipful Sycophant
Posts: 240
Joined: Mon May 14, 2007 6:45 pm UTC
Location: Wisconsin
Contact:

Re: Age of the Moon

Postby knight427 » Tue Dec 07, 2010 7:02 pm UTC

gmalivuk wrote:I didn't look at the paper, but didn't Zamfir say the graph in the article collapses 2-3 billion years ago, contrary to your claim in the OP of 1 billion years?


If he is referring to Figure 14 on page 1957 then I don't understand the graph. To me it looks as if the orbit collapses 1 billion years ago. The Time axis is hard to read, but I'm pretty sure it is t[10^9 years] and runs from -2 to +2. There is no explanation of when 0 is, so I assumed it was "today", then the orbit is graphed from 1 billion years ago out to 2 billion years from now. This would then behave similarly to the 3 previous tidal models they investigated which also collapse at about the same time. Here is what teh paper says after analyzing prevous models, but before presenting their own,

“The evolution of the lunar semimajor axis presents a well known time scale problem; the lunar orbit collapses only a little over a billion years ago.”

That's on page 1954.

gmalivuk wrote:In any case, the moon's orbit is changing because of gravitational effects of the tidal bulge it causes in Earth's oceans. Which means the configuration of said oceans should have a nontrivial effect over these kinds of timescales. Is that taken into account in the linked article?


The model is probably more focused on tidal bulge than anything else, though there are many other factors. But they do indeed mention tidal constants changing with continental drift as one factor not included. I'm a bit confused by what they are saying about it, follows the quote from above on page 1954. Check it out.
knight427



If you GIVE a zombie a fish, you will feed him for minute.

If you TEACH a zombie to fish, he will be munching on you for hours.

User avatar
Zamfir
I built a novelty castle, the irony was lost on some.
Posts: 7604
Joined: Wed Aug 27, 2008 2:43 pm UTC
Location: Nederland

Re: Age of the Moon

Postby Zamfir » Wed Dec 08, 2010 7:28 am UTC

You are right, I misread the graph.

User avatar
knight427
Worshipful Sycophant
Posts: 240
Joined: Mon May 14, 2007 6:45 pm UTC
Location: Wisconsin
Contact:

Re: Age of the Moon

Postby knight427 » Fri Dec 10, 2010 5:55 am UTC

I think I might have found the answer.

http://www.agu.org/journals/ABS/1982/RG ... 0457.shtml

The review claims this research resolves the time problem. They investigated the effect of different continental arrangements and determined that factor was not significant. The important factor seems to be that current tidal dissipation rates are historically high, so projecting the orbit back without compensation cause premature collapse. The factor changing this rate has something to do with "frictional coupling".

Just thought I'd share in case anyone else was interested.
knight427



If you GIVE a zombie a fish, you will feed him for minute.

If you TEACH a zombie to fish, he will be munching on you for hours.


Return to “Science”

Who is online

Users browsing this forum: No registered users and 12 guests