MORE EVIDENCE THAT MOON IS FORMED WHEN YOUNG EARTH COLLIDED WITH ANOTHER CELESTIAL BODY

German scientists said Thursday that moon samples collected during the 1960s and 1970s have shown new evidence that the moon formed when a young Earth collided with another celestial body. The smashup between an early form of Earth and a planetary body named Theia some 4.5 billion years ago is put forth by what scientists call the Giant Impact Hypothesis of moon formation. While most experts support the notion, they say the only way to confirm such an impact is to study ratios between the isotopes of oxygen, titanium, silicon and others. Until now, researchers studying lunar samples that arrived on Earth via meteorites have found that the Earth and moon were quite similar in makeup. But using samples collected from the lunar surface by NASA’s Apollo 11, 12 and 16 moon missions, and more advanced scientific techniques, scientists found something new. “They were able to detect a slightly but distinctly higher composition of the oxygen isotope in the lunar samples,” said the study in the journal Science.READ MORE...

ALSO: Body that formed the Moon came from a different neighborhood

The giant impact hypothesis goes like this: 4.5 billion years ago, a Mars-sized body named Theia slammed into the Earth. The collision launched magma—some from Theia and some from Earth—into orbit around our planet. The magma condensed and cooled into the rocky sphere that we see in the sky, our Moon. This scenario—explored through collision models—handily explains the way that our Moon spins, its small core, and its lack of water. It is the most widely accepted scientific response to the question of how the Moon came to be hung in our sky. But the giant impact hypothesis has suffered from one major problem: multiple analyses of lunar rocks suggest that the moon is made up of the same material as Earth. Collision models peg the moon at 70-90 percent material from Theia, and most bodies in our Solar System have very different compositions. READ MORE...

ALSO: Did an impact knock the Moon on its side?

We tend to think of the Moon as a static, dead world, with no atmosphere and no plate tectonics. But there are various signs the Moon has been active—volcanoes and indications of a magnetic field frozen in rocks. Impact craters that flooded with molten rock are also indications of more active periods in the Moon's history. Now, some researchers are suggesting that the residual magnetic fields contain hints that the Moon was once flipped on its side by a violent event. All evidence indicates that the Moon was formed when a Mars-sized body collided with the early Earth, leaving both in a molten state. This would have left the Moon with a sufficiently molten core that it should have generated a magnetic field for hundreds of millions of years. Remnants of that field should remain trapped in rocks that solidified while it was still in place and remain trapped there to this day. READ MORE...

ALSO: Dating the collision that formed the Moon using late-arriving debris

When did the Earth actually form? There are a number of ways to approach that question. We can use radioactive dating to look at material that has fallen to Earth after remaining largely undisturbed since the formation of our Solar System, or we can obtain a date for the oldest materials we've found on Earth. But those methods simply provide an upper and lower limit; the Earth formed some time after the smaller material in the Solar System, while the earliest materials on Earth would have been produced some time after its formation. Now, researchers have provided a new date for the formation of the Earth, based on the last time the planet was entirely molten—an event that was triggered by a collision with a body that ultimately created the Moon. The data is calculated using what we know about the early Solar System combined with the debris that fell to Earth after the big collision. READ MORE...


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More evidence that Earth collision formed Moon–study

MANILA, JUNE 9, 2014 (INQUIRER) Agence France-Presse
 


View of the moon in Cannes, southern France, on May 15, 2014.

German scientists said Thursday, June 5, that moon samples collected during the 1960s and 1970s have shown new evidence that the moon formed when a young Earth collided with another celestial body. AFP PHOTO/LOIC VENANCE

WASHINGTON–German scientists said Thursday that moon samples collected during the 1960s and 1970s have shown new evidence that the moon formed when a young Earth collided with another celestial body.

The smashup between an early form of Earth and a planetary body named Theia some 4.5 billion years ago is put forth by what scientists call the Giant Impact Hypothesis of moon formation.

While most experts support the notion, they say the only way to confirm such an impact is to study ratios between the isotopes of oxygen, titanium, silicon and others.

Until now, researchers studying lunar samples that arrived on Earth via meteorites have found that the Earth and moon were quite similar in makeup.

But using samples collected from the lunar surface by NASA’s Apollo 11, 12 and 16 moon missions, and more advanced scientific techniques, scientists found something new.

“They were able to detect a slightly but distinctly higher composition of the oxygen isotope in the lunar samples,” said the study in the journal Science.

“This very small difference supports the Giant Impact Hypothesis of moon formation.”

According to theoretical models of the collision, the moon would have formed mostly from Theia, at between 70-90 percent, with some 10-30 percent coming from Earth.

But researchers now say the moon could be a 50/50 mixture of Earth and Theia remnants, though more study is needed to confirm.

“The differences are small and difficult to detect, but they are there,” said lead author Daniel Herwartz of Georg-August-Universitat Gottingen.

“We can now be reasonably sure that the Giant collision took place.”

The findings will be presented at the Goldschmidt geochemistry conference in California on June 11.

FROM ARS TECHNICA

Body that formed the Moon came from a different neighborhood by Shannon Palus June 6 2014, 11:37am EDT PHYSICAL SCIENCES SPACE

The body that smacked into Earth has a distinctive elemental signature.


A lunar rock, which contains a distinctive isotopic signature from those of Earth rocks. Addi Bischoff, Westfälische Wilhelms-Universität Münster

The giant impact hypothesis goes like this: 4.5 billion years ago, a Mars-sized body named Theia slammed into the Earth. The collision launched magma—some from Theia and some from Earth—into orbit around our planet. The magma condensed and cooled into the rocky sphere that we see in the sky, our Moon.

This scenario—explored through collision models—handily explains the way that our Moon spins, its small core, and its lack of water. It is the most widely accepted scientific response to the question of how the Moon came to be hung in our sky.

But the giant impact hypothesis has suffered from one major problem: multiple analyses of lunar rocks suggest that the moon is made up of the same material as Earth. Collision models peg the moon at 70-90 percent material from Theia, and most bodies in our Solar System have very different compositions.

But based on examinations of lunar rocks, it's as though the big collision never happened. It is “maybe the last major problem” with the giant impact hypothesis, says geochemist Daniel Herwartz, who also thinks he has solved it. In a paper published in Science on Thursday, he reported that the Moon does, in fact, contain a tell-tale sign of alien material.

To Herwartz—or anyone studying lunar rocks with the intention of figuring out their origin—all rocks have a sort of cosmic address label. Since ratios of isotopes (versions of an element with different numbers of neutrons) on the Earth, Mars, and asteroids are unique, we know that our young Solar System was “isotopically heterogeneous.” The isotopes in a rock reveal exactly where in the Solar System it formed.

Differences in oxygen isotope levels are particularly dramatic. According to previous readings of moon-rock oxygen, the difference between a key oxygen isotope measurement—the ratio between three variations of oxygen, specifically—appeared to be just 3 parts per million higher on the Moon than on Earth, a difference so small as to be negligible. Against the evidence from collision models, the Moon’s address label suggested that it was made mostly or entirely of Earth.

Herwartz thought that maybe the difference was more than statistical variance. He took samples from the Apollo 11, 12, and 16 missions (lunar samples that fell to Earth were too contaminated). Using a high-precision method published earlier this year, he released the oxygen by heating it in a container with fluorine gas, purified it, and then measured the isotope ratios in a gas mass spectrometer.

On this re-evaluation, he found that the ratio between to oxygen isotopes on the Moon was, in fact, different: 12 parts per million higher on the Moon than on Earth.

This difference confirms that the Moon is not made of material that formed in the same region as Earth, and, most importantly, that it’s not merely a chunk of Earth. The isotope difference is still not terribly large—Mars and the Earth differ by a factor of 300 ppm, for example. But that suggests Theia probably formed in a region of the solar system near Earth.

As for how much of the Moon is Theia and how much is Earth—that’s still a mystery. After colliding with Earth, Theia ceased to exist as an independent body. Collision models peg the ratio at 70 percent to 90 percent. Herwartz suspects that it's closer to 50/50, but that’s just an informed guess at this point.

The details may be fuzzy, but as Herwartz said in a statement: “we can now be reasonably sure that the giant collision took place.”

Did an impact knock the Moon on its side? by John Timmer - May 9 2014, 7:00am EDT EARTH SCIENCE PHYSICAL SCIENCES

Anomalies suggest the far side and pole weren't always where they are today.


serguei_30

We tend to think of the Moon as a static, dead world, with no atmosphere and no plate tectonics. But there are various signs the Moon has been active—volcanoes and indications of a magnetic field frozen in rocks. Impact craters that flooded with molten rock are also indications of more active periods in the Moon's history.

Now, some researchers are suggesting that the residual magnetic fields contain hints that the Moon was once flipped on its side by a violent event.

All evidence indicates that the Moon was formed when a Mars-sized body collided with the early Earth, leaving both in a molten state. This would have left the Moon with a sufficiently molten core that it should have generated a magnetic field for hundreds of millions of years. Remnants of that field should remain trapped in rocks that solidified while it was still in place and remain trapped there to this day.

FURTHER READING: Tracking geologic hotspots shows a wobbly Earth in constant flux.


NO ABSOLUTES: HOW SHIFTING PLATES COMPLETELY REMAKE THE EARTH

A team of Japanese researchers has now analyzed magnetic data from two lunar orbiters, the Lunar Prospector and Kaguya.

Both orbited the Moon at low altitudes (under 40km) and tracked the local magnetic fields. After eliminating a variety of areas with complex magnetic anomalies, the team looked at data from 57 different sites on the Moon and used the readings to calculate the orientation of the Moon's magnetic field at various points in its past.

Many of the data points clustered at the current pole. But a second set clustered well away from there, somewhere between 45 and 60 degrees from the existing pole. Although the Earth has experienced some degree of polar wander, the pole has always made a gradual track as the Earth's angular momentum shifted.

Here, it appears that the Moon made a sudden jump, as there are no indications of gradual track between these two locations.

As the authors note, "A change in the apparent pole position corresponds to a reorientation of the lunar surface with respect to the rotation axis." And this reorientation appeared to occur relatively suddenly.

The authors suggest a number of events could have been the cause, including giant impacts, internal instabilities, and the gravitational disturbances caused by migrations of the Solar System's gas giants.

This isn't the first indication that the Moon may have shifted its orientation. An earlier work examined the distribution of craters on its surface, which should be biased toward a greater number on the far side. Instead, some researchers have suggested the near and far side of the Moon swapped places at some point in the distant past.

Neither of the methods of tracking this shift have been precise enough to indicate when this event took place, which might allow us to associate it with some of the Moon's larger impact basins. But there certainly seems to be enough evidence of this sort of shift to make the idea worth exploring further.

Dating the collision that formed the Moon using late-arriving debris by John Timmer - Apr 2 2014, 1:36pm EDT EARTH SCIENCE

The magma ocean that resulted acted like a reset button on the age of the Earth.


That's gotta hurt. The collision that formed our Moon might have left the entire Earth molten.
NASA

When did the Earth actually form? There are a number of ways to approach that question. We can use radioactive dating to look at material that has fallen to Earth after remaining largely undisturbed since the formation of our Solar System, or we can obtain a date for the oldest materials we've found on Earth. But those methods simply provide an upper and lower limit; the Earth formed some time after the smaller material in the Solar System, while the earliest materials on Earth would have been produced some time after its formation.

FURTHER READING: Novel analysis confirms its 4.4 billion year age.


THE OLDEST PIECE OF THE EARTH, EXAMINED ATOM-BY-ATOM

Now, researchers have provided a new date for the formation of the Earth, based on the last time the planet was entirely molten—an event that was triggered by a collision with a body that ultimately created the Moon. The data is calculated using what we know about the early Solar System combined with the debris that fell to Earth after the big collision.

The early Solar System was a violent place, as small particles aggregated into bodies that then grew larger by collisions. These collisions eventually produced planetesimals the size of large asteroids, which merged to form the current collection of planets. So there was no clear start to what would ultimately become the Earth, but there was a clear end to the primary process of its formation.

That end came when the proto-Earth was smacked by a Mars-sized body. The resulting collision would have left the Earth a magma ocean, blown away its atmosphere and any volatile liquids on its surface, and put enough debris in orbit to form the Moon. In effect, it acted like a reset button for the timing of the Earth's formation, remixing all its components so that the raw material for radioactive dating—the stable maintenance of isotope differences caused by radioactive decay—was eliminated. Everything started afresh.

Figuring out the timing of that collision is important if we want to understand the conditions on the early Earth and in the early Solar System in general. The new study uses a clever way of providing an estimate, based on the fact that the last major collision in the Earth's history didn't mean that the Earth escaped further bombardment from space.

The logic is pretty clever. In the wake of the Moon-forming collision, the entire Earth was molten, which allowed the iron to sink to the core. A number of heavy elements that have an affinity for iron sunk to the core with it. This would have left the surface of the Earth completely stripped of these metals. (These elements, which include gold and platinum, are generically referred to as siderophiles.) But it's possible to mine this material from the crust.

The elements are there because the Earth's supply was partly refreshed by the arrival of new material in collisions with other planetesimals and smaller asteroids. (The most famous asteroid, the one that killed the dinosaurs, was first identified through the presence of a layer of another siderophile, iridium, which it carried to Earth.) If we total how much of these elements are in the crust and compare that number to the composition of asteroids in our Solar System, we can get an estimate of how much mass must have struck the Earth after the Moon-forming collision.

How do you go from that mass to a date? The authors recognized that over time, these bodies were lost through collisions with Earth and the other planets. Thus, early in the Solar System's history, there was an ever-shrinking stock of planetesimals that could have delivered material to Earth. To find out the timing of when the stock was depleted, the researchers relied on models of Solar System formation.

In fact, they relied on two different types of models: one that keeps the giant outer planets in their current locations and a second class in which Jupiter and Saturn engage in what's called a "Grand Tack," moving inward early in the Solar System's history before receding back out to their current locations. The Grand Tack simulations were more likely to produce a set of rocky inner planets that look like our Solar System, but in both cases, the planetesimals got depleted pretty rapidly.

Their vanishing act sets limits on when the Moon-forming collision could have happened and, thus, when the Earth could have formed. Too early, and the Earth would have seen lots of additional collisions and had its crust loaded with the elements that are now rare. Too late, and there wouldn't be enough around to give us any significant quantities. Consequently, the authors calculate that there's only a 0.1 percent chance that the Moon-forming collision took place prior to 40 million years after material started condensing in our Solar System. Instead, they place the likely date at 95 million years, with a margin of error of 30 million years on either side.

The authors suggest that we might want to revisit some of the results that were generated using isotope data—a few of these put the collision at 30 million years, and understanding why they got the number wrong may provide some details of the mechanics of the collision itself.

They also think that the reloading of the Earth with rare metals tells us something about the distribution of mass during the formation of the Solar System, which can constrain our models of planet formation. Right now, those models don't do a very good job of creating many of the tightly packed systems that we're currently discovering, so any improvements to them would be a positive step.


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