New isotopic evidence supporting moon formation via Earth collision with planet-sized body

Jun 05, 2014
Thin section of an enstatite chondrite fragment from the asteroid Almahatta Sitta (official name: 2008 TC3). This fragment was observed on 7 October 2008 in the Nubian Desert, Sudan. Credit: Addi Bischoff, Westfälische Wilhelms-Universität Münster

A new series of measurements of oxygen isotopes provides increasing evidence that the Moon formed from the collision of the Earth with another large, planet-sized astronomical body, around 4.5 billion years ago. This work will be published in Science on June 6, and will be presented to the Goldschmidt geochemistry conference in California on 11th June.

Most believe that the Moon formed from an impact between the Earth and a planet-sized body, which has been given the name Theia. Efforts to confirm that the impact had taken place had centred on measuring the ratios between the isotopes of oxygen, titanium, silicon and others. These ratios are known to vary throughout the solar system, but their close similarity between Earth and Moon conflicted with theoretical models of the collision that indicated that the Moon would form mostly from Theia, and thus would be expected to be compositionally different from the Earth.

Now a group of German researchers, led by Dr. Daniel Herwartz, have used more refined techniques to compare the ratios of 17O/16O in lunar samples, with those from Earth. The team initially used which had arrived on Earth via meteorites, but as these samples had exchanged their isotopes with water from Earth, fresher samples were sought. These were provided by NASA from the Apollo 11, 12 and 16 missions; they were found to contain significantly higher levels of 17O/16O than their Earthly counterparts.

Dr Herwartz said "The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia. Theia seems to have been similar to what we call E-type chondrites**.If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth. The next goal is to find out how much material of Theia is in the Moon".

Lunar meteorite Kalahari 008. Impacts on the Moon can eject lunar material, which may then fall to the Earth. Kalahari 008 is an approximately 600g meteorite from the Moon that was collected in 1999 in the Kalahari Desert, Botswana. Credit: Addi Bischoff, Westfälische Wilhelms-Universität Münster

Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.

The team used an advanced preparation technique before measuring the samples via stable isotope ratio mass spectrometry, which showed a 12 parts per million (± 3 ppm) difference in 17O/16O ratio between Earth and Moon.

Explore further: Lunar rock samples reveal variations in water concentrations

More information: "Identification of the giant impactor Theia in lunar rocks," by D. Herwartz et al. Science, 2014. www.sciencemag.org/lookup/doi/… 1126/science.1251117

Dr Daniel Herwartz will present "The elevated Δ17O composition of the Moon relative to the Earth" to the Goldschmidt conference, Sacramento, California, on 11th June at 09.45, Eastern Time.

Journal reference: Science search and more info website

Provided by European Association of Geochemistry

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Osiris1
1 / 5 (4) Jun 05, 2014
It has been posited elsewhere that the Earth had a solid surface and areas cool enough to allow life as little as a hundred million years after formation or less. With the cataclysmic collision theorized as occurring up to four hundred million years later, we then are forced to face questions of what kind of life either arrived or arose here in that very ancient period. Possibly there may have even been life on 'Theia' up to its collision. And...whatever became of Theia. Maybe Theia is Mars or maybe Venus. Not likely the asteroid belt as its total mass is not large enough to fit current theories of mass collision forming our moon. Next question is where would we look for evidence of such life. Our crust recycles itself so maybe difficult to find here, but the Moon is another story. We have a very large open and scarred area of the ocean floor in the Pacific. Maybe here is where the collision took place.
Caliban
5 / 5 (4) Jun 05, 2014
It has been posited elsewhere that the Earth had a solid surface and areas cool enough to allow life as little as a hundred million years after formation or less. With the cataclysmic collision theorized as occurring up to four hundred million years later, we then are forced to face questions of what kind of life either arrived or arose here in that very ancient period. Possibly there may have even been life on 'Theia' up to its collision. And...whatever became of Theia. Maybe Theia is Mars or maybe Venus. [...] Our crust recycles itself so maybe difficult to find here, but the Moon is another story. We have a very large open and scarred area of the ocean floor in the Pacific. Maybe here is where the collision took place.


@Osiris,

If you have a link regarding "We have a very large open and scarred area of the ocean floor in the Pacific. "

I would be very interested to see it. Do you mind posting?

I would be information I hadn't encountered before.
Torbjorn_Larsson_OM
4.2 / 5 (5) Jun 05, 2014
The problem with enstatites is that they may be derived from the part of the asteroid belt closest to Mars. (The E-belt, that later became the Hungarians.) That makes for a Theia, but it was also part of the late bombardment. [ http://www.lpi.us...1269.pdf ]

The cold early Earth was present ~ 50 Ma after that, ~ 4.4 Ga before present. That's a fairly certain date now, with microanalysis of the oldest zircons. [ http://arstechnic...by-atom/ ]

[tbctd]
Torbjorn_Larsson_OM
5 / 5 (6) Jun 05, 2014
[Oops, the editor messed up my comment, The last part was a response. I'll repost:]

The problem with enstatites is that they may be derived from the part of the asteroid belt closest to Mars. (The E-belt, that later became the Hungarians.) That makes for a Theia, but it was also part of the late bombardment. [ http://www.lpi.us...1269.pdf ]

@Osiris1: I don't think it was ever possible with a 400 Ma delay, more like 250 Ma depending on uncertainties of Moon crater datings vs Apollo sampling.

Anyway, recently they found another way to date the Moon that had much less uncertainty, by late accretion dating. The Tellus-Theia collision that formed Earth-Moon happened 95 +/- 32 Ma after the protoplanetary disk started to condense. [ https://docs.goog...TM0/edit ]

[tbctd]
Torbjorn_Larsson_OM
4.8 / 5 (6) Jun 05, 2014
[ctd]

The cold early Earth was present ~ 50 Ma after that, ~ 4.4 Ga before present. That's a fairly certain date now, with microanalysis of the oldest zircons. [ http://arstechnic...by-atom/ ]

The new find means Theia was ~Mars sized, the main model, in which case all of it went into the Earth-Moon formation.

Sure, protoplanets like Theia and Mars formed in ~ 3 Ma as opposed to Tellus ~ 30 Ma, but they all could have had life at the time of the collision. We will likely only know if we can find such early life on Mars. Remember, Tellus was remelted and Theia vaporized, and the Moon formed out of hot ejecta, so neither Earth nor Moon will likely retain pre-impact traces of putative life.
Torbjorn_Larsson_OM
5 / 5 (8) Jun 05, 2014
@Osiris, Caliban:

The idea that Earth shows scars from Theia is pre-plate tectonics theory. Earth was reheated and reformed, that's why geologists want to call the protoplanet Tellus and the post-collisional body Earth. And all later continents and oceans are formed and moved around by plate tectonics.
Frank_Lowe
1 / 5 (5) Jun 06, 2014
The Moon is from the Earth it is a spin of.Just like all the planets is spin offs from the Sun.Just look at their compositions and where they are when the Sun started to heat up or was borne.
Caliban
5 / 5 (3) Jun 06, 2014
@Osiris, Caliban:

The idea that Earth shows scars from Theia is pre-plate tectonics theory. Earth was reheated and reformed, that's why geologists want to call the protoplanet Tellus and the post-collisional body Earth. And all later continents and oceans are formed and moved around by plate tectonics.


Torbjorn,

Thanks for that. My understanding of the best evidence to date is right in line with your comments, especially with regard to your last.

That was why I was puzzled by Osiris's Pacific basin scarring.

Torbjorn_Larsson_OM
5 / 5 (5) Jun 06, 2014
@Frank_Lowe:

Of course they aren't!

You can't get the orbital mechanics to work out.

And besides that disk formation and then planet formation is the accepted, working mechanism, and predicts the same composition from a much simpler pathway (disk condensation, then planet condensation instead of very many "spin off" events), we have now seen very many such protoplanetary disks and the emerging planets within them. (We see the emergence as condensations and their making gaps in the disk.) Those disks are _only_ seen around young stars.

This is encyclopedic knowledge these days: "Protoplanetary disks have been observed around several young stars in our galaxy." [ http://en.wikiped...ary_disk ; http://en.wikiped...ormation ] See the images, and you can find more on the web.
matt_roadhouse
1 / 5 (2) Jun 06, 2014
exact same time life appeared on earth ... interesting
Caliban
5 / 5 (3) Jun 06, 2014
exact same time life appeared on earth ... interesting


What exactly do you mean by that statement?

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