Where did the Moon come from?

[Leovinus]

Assume that something blasted the Moon out of the Earth. Also assume that the continents were once all joined (Tangea I think it is called).<br /><br />Do you think the Moon came from the anti-Tangea side of the Earth (Pacific Ocean?) or from the Tangea side? In other words, would the departing Moon leave a depression or a high region as it left? <div class="Discussion_UserSignature"> </div>

 

[lunatio_gordin]

I think the Moon collision occurred before Pangea or any of the continents as such were in existence. Earth was still pretty much molten, as i understood it.<br /> what i see here is that The Moon formed about the same time as everything else, so if it originally came from the earth, it would have to occur very early in Earth's history. The iron from the Mars body's core and any iron knocked off earth falls back, and the other things eventually coalesced into the moon.<br />So i don't really think that earth existed in that state yet. And there probably wouldn't be any marks left due to plate tectonics over the vast time period...

 

[najab]

As I understand it, the impactor was about the size of Mars. Earth was almost totally shattered by the impact, all trace of any pre-existing continents would have been erased.

 

[silylene old]

One hypothesis is that 2/3 of the Earth's original crust was lost in the collision, and coalesced as a part of the moon. This hypothesis is consistent with simulations, and consistent with elemental analysis of moonrocks.<br /><br />And possibly, because a substantial amount of crust was lost, the remaining crustal fragments had room to move around on a thin crust, giving rise to continental drift. In contrast, our sister planet Venus, with its original thick crust, has no continental drift. Is this hypothesis correct? Who knows, but it is interesting. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[najab]

I'd never heard that one before, but it is interesting and makes a <b>lot</b> of sense.

 

[Saiph]

another possible explaination for the venus-earth discrepancy, is that a sphere in space can IIRC develope two types of convection. Either a symetrical, all round set of convection from the center out (like earth). Or it can develope a single mass convection cell, from one side of the sphere to the other, through the center. So one side spreads out, shifts to the other side, where it dives in, goes through the center, and the hot material rises out the original side, cools, pulls around, and goes into the center again. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[tomnackid]

The name of the supercontinent was "pangea", Greek for "all earth". Contrary to popular belief the earth did not start off with one continent that later broke up. The continents have been breaking up and colliding since the crust cooled to a solid state. It just happens that at one point during the messozoic era (the age of reptiles) they all came together into one giant continent.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>Any kind of depression or high region left from the glancing blow by the Mars-sized object would quickly flatten out, since the Earth was much closer to it's original molten state then.<p><hr /></p></p></blockquote><br /><br />And even if it weren't molten, such an impact would probably remelt a large portion of the planet anyway. That's one heck of an impact, really. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[joshbe]

Well, It was actually Pangea. I belive that the mars size object smashed in to the Earth when it was still a forming planetoid. This would mean there were no continents. Yet I belive that the Earth was solid enough to have and enourmous crater -like feature (the Pacific) rather than balling up again.

 

[earthseed]

The moon formed over four billion years ago. Pangea formed about 300 million years ago from the collision of several continents. This cycle of a super-continent forming and breaking up (called a Wilson Cycle) has happened at least four times (probably more) since plate tectonics began. Therefore the "Pacific Ocean", in its various incarnations, has been created and destroyed several times. The present Pacific Ocean has absolutely nothing to do with the formation of the moon.<br /><br />By the way, a good article on how the formation of the moon affected plate tectonics on Earth may be found here.