The collision between "Proto-Earth" and Theia, from which the Earth and Moon were created 4,500-4,400 million years ago. Both planets had a massive iron core when they collided and created the Moon and Earth.

The Earth and Moon May Have Formed Later Than Previously Thought

8 Jun , 2010 by

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The Earth and Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now it was thought to have happened when the solar system was 30 million years old or approximately 4.5 billion years ago. But new research shows that the Earth and Moon may have formed much later – perhaps up to 150 million years after the formation of the solar system.

“We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision,” said Tais W. Dahl, from the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

The planets in the solar system were created by collisions between planetary embryos orbiting the newborn sun. In the collisions the small planets congealed together and formed larger and larger planets. When the gigantic collision occurred that ultimately formed the Earth and Moon, it happened at a time when both planetary bodies had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

The age of the Earth and Moon can be dated by examining the presence of certain elements in the Earth’s mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into the Earth’s core. But did all the tungsten go into the core?

“We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth’s early formation remain in the rocky mantle,” said Tahl.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

“Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometers in diameter and therefore that most of the Earth’s iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation” said Dahl.

The result of the research means that collision that created the Earth and the Moon may have occurred as much as 150 million years after the formation of the solar system, much later than the 30 million years that was previously thought.

The research results have been published in the scientific journal, Earth and Planetary Science Letters.

From a University of Copenhagen press release.

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Ravenas
Member
Ravenas
June 8, 2010 12:28 PM

I do not get it. Please explain. So how old is Earth and Moon then?

Kevin
Member
Kevin
June 8, 2010 1:30 PM

120 million years later!!?!?!?!?!? This changes EVERYTHING!!!!!!@!!!111111

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 8, 2010 4:26 PM

It is a result from a model, and its later dates clashes with what we know. The first zircons measured at 4.4 Ga formed in an environment with a liquid water reservoir.

I’m sorry, but it just doesn’t seem very likely to me.

This changes EVERYTHING!!!!!!@!!!111111

Yes. Yes, it does. See above.

stuartajc
Member
stuartajc
June 9, 2010 4:03 AM

“It takes 50-60 million years for all hafnium to decay and be converted into tungsten”

Err, that’s not how half life works. It takes theoretically an infinite time for ALL of it to decay

Hf 182 has a half life of 9 million years, so most of it will have gone in 50-60 million years, but not all

Emilio
Guest
Emilio
June 9, 2010 4:40 AM

If entire life history of earth is equated to a year, moon formed on the 3rd day in January. The new study put it on the 12th day in January. And us, Homo habilis, did not appear until 5 hour before the last day of December!

neoguru
Member
neoguru
June 9, 2010 5:36 AM

I’ve been very curious about the state of Venus and the apparent recent melt-down of it’s surface. Is there any evidence that it may have been due to a collision?

Quasy
Member
Quasy
June 9, 2010 6:42 AM

I was wondering if this collision has anything to do with the diferent rotation speed of the iron core of Earth. If the collision was at a shallow angle, then it may have given a larger rotation speed to the molten earth. As the mantle cooled down, the rotation was slowed (and stabilised) by the moon, but the molten core continued to rotate at a different speed (giving us today the earth’s magnetic field).

Emilio
Guest
Emilio
June 9, 2010 7:01 AM

The collision may have affected earth spin. But have you try to spin a raw egg? It is difficult to do that because it is not a sold. So if earth was a puddle of molten object back then, collision may not have cause a spin.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 9, 2010 10:36 AM
I’ve been very curious about the state of Venus and the apparent recent melt-down of it’s surface. Is there any evidence that it may have been due to a collision? It appears that theory has been observationally challenged. “Map relations illustrate that the RTT displays planet-scale patterns that, together with altimetry, record a rich geologic history.” (But the work is behind a paywall, so I can’t say more.) Interestingly, there is a collision proposal that predicts Venus’ slow retrograde rotation and absence of water and plate tectonics, without necessarily resulting in a moon. But it is an early accretionary planetesimal collision scenario. the molten core continued to rotate at a different speed (giving us today the earth’s magnetic… Read more »
Spoodle58
Member
June 9, 2010 12:19 PM

That is correct stuartajc,
‘Nearly all’ would have been a better thing to say, with 98.4% of Hf 182 decayed to W 182 in 53.4 million years.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 9, 2010 3:07 PM

D’oh! “its FeS eutectic starting composition” ; it’s tending to the eutectic; my bad.

IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
June 9, 2010 4:13 PM

We seriously need a preview/edit facility here, don’t we, Torbjörn?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 10, 2010 8:42 AM

YES, indeed, IVAN#MAN!!!

Right next to the vote box for good posts/suggestions.

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