Theia Impact: How Did the Earth's Hole Disappear?

[darksoda]

Hey people i have a doubt o try to be more specific this time, theia the planet collided with the Earth and created the moon this impact destroyed a large part of the Earth make a hole, what i like to know is how this hole who the planet Theia create on Earth disappeared, i mean the impact destroy a part of Earth what fill this hole? i hope i was specific enough.

here some link of the impact of the planet Theia with Earth
http://pt.wikipedia.org/wiki/Ficheiro:Big_Slash.gif

 

[LURCH]

In most models, this impact happened while both bodies were still forming. At this stage in development, both protoplanets would still be largely molten. And even if they weren't, the energy of such a tremendous collision would have melted them both anyway. So both bodies were shattered and mostly melted by the collision, and then fell back into roughly spherical shape while behaving mostly like liquids under gravity's pull. The impact didn't leave a crater, in much the same way that a ship doesn't leave a trench across the water.

 

[darksoda]

thanks for the answer :D let me see if i understand, so the part of the impact became the spherical shape who was made of pieces of both planets and made also of melting parts ?

 

[LURCH]

thanks for the answer :D let me see if i understand, so the part of the impact became the spherical shape who was made of pieces of both planets and made also of melting parts ?

Pretty much. Might be clearer to think of the collision resulting in both rocky bodies being blown apart to form a cloud of debris. This cloud would have had two areas of higher density; the remains of the centers of the two original bodies. From there, the whole process of planetary formation starts over, from the accretion disc phase onward. The lighter elements float to the top of the cloud while the heaviest ones sink to the bottom. The two areas of higher density gather the accretion disk into two bodies, rather than one. So there is no crater because both of the original bodies were totally destroyed, their pieces mixed together, and two entirely new bodies formed from the resulting cloud.

 

[darksoda]

Pretty much. Might be clearer to think of the collision resulting in both rocky bodies being blown apart to form a cloud of debris. This cloud would have had two areas of higher density; the remains of the centers of the two original bodies. From there, the whole process of planetary formation starts over, from the accretion disc phase onward. The lighter elements float to the top of the cloud while the heaviest ones sink to the bottom. The two areas of higher density gather the accretion disk into two bodies, rather than one. So there is no crater because both of the original bodies were totally destroyed, their pieces mixed together, and two entirely new bodies formed from the resulting cloud.

thanks very much :D

 

[Ophiolite]

Pretty much. Might be clearer to think of the collision resulting in both rocky bodies being blown apart to form a cloud of debris.

While it may be clearer to think of it this way, and 'this way' applies to the formation of the moon, there is no evidence to suggest this is what occurred for the proto-Earth. The suggestion runs counter to any generally accepted view of the process. Perhaps I am missing some interesting research. Can you provide a citation for the debris cloud model please?

 

[Chronos]

The 'giant impacter' hypothesis, while popular, still lacks compelling evidence. No one has suggested a believable model that explains how the moon coalesced from a debris cloud in less than a billion years. Radioactive dating of rocks collected from the lunar surface during Apollo missions indicates they are nearly 4 billion years old. That is as old, or older, than the most ancient rocks collected from the surface of earth. A lunar core sample would be very interesting. IMO, the evidence still suggests the moon is a companion planet formed from the same circumsolar debris as earth.

 

[Ophiolite]

The 'giant impacter' hypothesis, while popular, still lacks compelling evidence. No one has suggested a believable model that explains how the moon coalesced from a debris cloud in less than a billion years..

Yet models for how it coalesced within a few million years are accepted by the vast majority of planetary scientists. You are free to disbelieve such models, but it is unscientific to suggest you reflect the strong consensus of researchers on this topic.

Radioactive dating of rocks collected from the lunar surface during Apollo missions indicates they are nearly 4 billion years old. That is as old, or older, than the most ancient rocks collected from the surface of earth.

Incorrect. The oldest moon rocks, from the highlands, have been dated at 4.5 billion years old. i.e. an age consistent with the formation of the moon via impact about 50 to 100 million years after the initial formation of the solar system.

I don't understand what significance you see in the absence of older rocks on the Earth. Here rocks are recycled by plate tectonics. We do have remnant zircons, notably from Jack Hills, whose age has been placed around 4.4 billion years, but again what does that have to do with the validity of the giant impact hypothesis?

No hypothesis can be proven, only dis-proven, and there are some interesting challenges to it, yet it remains - currently - the best explanation for the observed facts.

IMO, the evidence still suggests the moon is a companion planet formed from the same circumsolar debris as earth.

Noted, but for your opinion to be given any attention you need to present your interpretation of the evidence, with justification, rather than simply expressing personal incredulity.

 

[jim mcnamara]

Usually you reject a hypothesis. Disproving means testing all possible cases and finding them false. In this case, however, it might just be a language issue. I cannot tell.

But you are correct in the direction you are going (cannot not know about the details of your assertions), one attempts to find support for a hypothesis. If one cannot do that, then one abandons the hypothesis for a better one. I am guessing there are multiple models and therefore different hypotheses at work here.

Bottom line: please back up assertions with some kind of citation from a refereed journal - linked ones are appreciated by old guys like me. Both of you, please. This is a really interesting topic! And I love debates based on logic and reasonable research results.

 

[Ophiolite]

Well, I shall provide the citations you request, but I find it runs counter to what I understood to be the ethos on this forum: namely those proposing something at odds with current conventional wisdom are the ones required to provide the back up. Would you ask me to support a claim for extinction of the dinosaurs by the Yucatan bolide? I suspect not, yet you wish to see this for something that has equal, or more professional support.

It may take a day or so to assemble appropriate material, but I shall comply.

(And just to be absolutely clear. I am not making an assertion, I am presenting the consensus view. It really isn't my fault if others are unfamiliar with it.)

Re the disproving of hypotheses: it is generally considered that a rabbit in the Cambrian would play merry hell with the theory of evolution.

 

[Evo]

Good article http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=446

 

[Ophiolite]

The overwhelming consensus view among scientists today is that the moon formed following the impact of a Mars sized planet (Theia) on the proto-Earth during the early stages of the formation of the solar system. A huge volume of material was thrown into space, much of it at such speed it was able to escape the gravitational attraction of the Earth. However, some remained in orbit as a debris disc that rapidly (perhaps in less than one hundred years) condensed and accreted to form the moon.

Any hypothesis for lunar formation has to account for several features of the moon:
• A comparatively large size relative to its parent. (The moon is ~1% of the mass of the Earth.)
• The large angular momentum of the Earth-Moon system
• Low lunar density, implying a major depletion in iron
• A lunar orbit once much closer to the Earth and inclined at 10° to the ecliptic

Data from the Apollo samples added further complications: the lunar composition bore striking similarities to terrestrial mantle material, but also striking differences. For example, the oxygen isotope ratios of mantle and lunar rocks differed from chondrites, the posited source for each, by similar amounts; however the moon was clearly seriously depleted in volatiles.

Three hypotheses were considered as plausible:
• Capture of a body formed elsewhere in the system
• Fission as a consequence of very high rotational speed of the proto-Earth
• Co-formation alongside the Earth

Each of these three hypotheses had serious problems. Consequently, two independent groups developed an alternative impact hypothesis: Hartmann and Davis in 1975 and Cameron and Ward in 1976. This idea languished until all four origin hypotheses were examined in detail in a 1984 conference in Hawaii, from which the impact hypothesis emerged as the clear winner.

Subsequent advances in computer power, especially using smooth particle hydrodynamics (SPH), have enabled detailed simulations that have refined the hypothesis and removed most of the contradictions, or remaining questions. In parallel with this, work on lunar geochemistry, especially isotope ratios, and the character and formation of the magma ocean, has complimented the dynamical findings. As a consequence, the impact origin of the moon is now generally accepted and work focuses on resolving any remaining inconsistencies.

Selected Bibliography:
Cameron, A.G.W. & Ward, W.R. The origin of the Moon. Lunar Sci.7: 120-122 (1976).
Canup,R.M. & Asphaug,E. Origin of the Moon in a giant impact near the end of the Earth's formation Nature 412: 708-712 (2001)
Canup R.M. Dynamics of Lunar Formation Annu.Rev.Astron.Astrophys.42: 441–75 (2004)
Hartmann, W.K. & Davis, D.R. Satellite-sized planetesimals and lunar origin. Icarus24: 504-515 (1975)
Hartmann,W.K.,Phillips R.J.,Taylor G.J.,eds. Origin of the Moon. Houston: LunarPlanet.Inst.781pp (1986)
Warren The Magma Ocean Concept and Lunar Evolution Ann. Rev. Earth Planet. Sci. 1985. 13: 201-40

Note: Evo's NASA link is excellent.

 

[jim mcnamara]

Notice I said 'Both posters'. Thanks for your extensive post. And apparently off-hand assertions need something like Evo's link - a very good one, BTW. That is very much PF-style. The 'everybody knows' approach does not fly, IMO.

Et tu Chronos?