Talk:Giant impact theory

Contents

1 Secondary disc 2 Single continent 2.1 Discuss article, not theory 3 References needed 4 Animation direction 5 Impactor tidal forces 6 Date of impact 4.533Ga 7 Why subtle growth?

Secondary disc

In my opinion "giant impact theory" has too many variables.The Moons origin can be explained by more subtle means.The Moon was born as a secondary disc,this secondary disc grew in the wake and shade of the Earths primary disc.The Earth and Moon orbited the sun in a "s" formation.As the Earths mass increased,it was forced away from the sun,as the Earth migrated this caused a collision of the protoplanets,protoplanetary discs are unstable the resulting clash of forces created the tilt of axis we see today,this clash of forces is also the trigger mechanism for the lunar orbit. — paulhesq

Single continent

I have very little knowledge of this subject, but would this be the reason there was one large continent? Is that what is meant by saying that the continents are made of a different type of rock than the ocean floors? the continents are the leftovers of the impact point? - Omegatron 18:53, Jan 9, 2005 (UTC)

There is no known relationship between there having been one single continent and this impact. Actually, from the composition of meteorites it appears that Earth should have a lot more of the less dense rocks which make up the continents. The Moon has a lot more of such lighter rocks than it should have. From your question about continents being leftovers of the impact point, perhaps you're thinking that the Earth was mostly nickel-iron and the impactor was made of lighter materials. We don't know, but it seems quite unlikely for Earth to have not had many of the less dense materials. Also, with such an impact, it seems unlikely that the impact site would have left much of a trace. In addition, continents are not a single piece of rock, and there have been many slow additions to continents detected. Start with craton for more info. (SEWilco 22:40, 30 May 2005 (UTC))

There was speculation at one point (1960s?) that the Pacific ocean basin could be a scar left over from the formation of the Moon. This was before plate tectonics was understood.

Also, Pangea coallesced from smaller continents, which were formed in the breakup of another mega-continent called Rodinia about 750 Ma (million years ago). Rodinia in turn had formed from the fragments of an even earlier supercontinent, and so on. However, the further back you go, the less continent there is, because while oceanic crust gets recycled, continental crust keeps growing. (Volcanic islands plastered onto the margins of continents add to their bulk.) It's speculated that very early in the Earth's history there were no continents at all; it was all oceanic crust.

If the Earth had kept all the lighter rocks that ended up in the Moon, we might have a lot more continent today. That could be a bad thing: without as much room for the plates to move around, continental drift could've stopped a long time ago, and the Earth might be much more like Venus. kwami 07:42, 2005 May 31 (UTC)

Discuss article, not theory

This page is for discussion of the Wikipedia article on the giant impact theory. It is not for discussion of the theory itself. --P3d0 02:56, Jan 28, 2005 (UTC)

Is there some reason Omegatron shouldn't be allowed to call attention to questions they feel are raised by and could be addressed in the article itself? --John Kenneth Fisher 03:00, May 30, 2005 (UTC)

I hope I didn't give that impression. --P3d0 02:29, Jun 1, 2005 (UTC)

References needed

This article is too good not to have any external links or references, We need the references that are referred to in the text, for a start. --Wetman 02:30, 28 Jan 2005 (UTC)

Animation direction

Doesn't the animation show the moon orbiring the earth in the wrong direction? I am assuming that we are looking "down" on the north pole as most literature show.

Common people, if you're going to put forth serious arguments, then you have to present the current facts correct. If Theia started at L4, then the animation is showing the Moon orbiting the Earth in the wrong direction!

Impactor tidal forces

how can a body orbit the earth and hit it "with a suitably low velocity" without being torn apart by tidal forces?

Date of impact 4.533Ga

The author of the article might want to incorporate this reference.

Conclusions: Luna is less than 65% Theia; impact occurred 4.533Ga.

 	Evolution of Planetary Cores and the Earth-Moon System from Nb/Ta Systematics
 	Carsten Münker, Jörg A. Pfänder, Stefan Weyer, Anette Büchl, Thorsten Kleine, and Klaus Mezger
 	Science 4 July 2003; 301: 84-87 [DOI: 10.1126/science.1084662]

Abstract It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 ± 0.3) and the Moon (17.0 ± 0.8) are below the chondritic ratio of 19.9 ± 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.

The anonymous contributor of the above did not explain that the ratio suggests that both the Earth and the Moon were subjected to unusually high pressures. Under this pressure, some Nb combined with mantle materials which it otherwise does not react with. The Moon's ratio being higher than Earth also suggests that its material was subjected to somewhat less pressure. (SEWilco 06:57, 1 Jun 2005 (UTC))

Why subtle growth?

Why formulate a subtle process of growth to explain the Lunar birth?

The accretion of planets is simply a process of growth, all such processes are subject to abnormality. Sometimes the trigger event for change is a monumental , sometimes change is triggerd by more subtle means. It is more probable that the instability of a young Sun triggerd the birth of our Moon. Co-accretion theorys have been dismissed in the past becaus they have failed to answer the density question. If all science had was a tadpole, might it be mistaken for fish fry? It would take a great deal of imagination to envisage the adult frog and its various stages of growth. Why does the Moon have to be born orbiting the Earth? If the young Sun suddenly erupted on the Earths magma core, a bow shock wave and wake would form. In the wake,in the shadow of the Earth a secondary core would form..... Primary secondary shadow accretion. paul.

I suppose compared to solar energies, Giant Impact could be called subtle. Is there an article about shadow accretion? (SEWilco 05:13, 1 Jun 2005 (UTC))