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Moon-crater survey could improve Solar System surface-dating methods.

Most of the fanfare surrounding the LRO has focused on the detection of water. But the LRO's detailed snapshots, some of which were presented last week at the Lunar Science Forum at the NASA Ames Research Centre in Moffett Field, California, are also yielding insights into the mechanics of asteroid and comet impacts and how frequently they occur - information that could improve estimates of the age of geological formations on other planets. The work, says planetary geologist Peter Schultz of Brown University in Providence, Rhode Island, "gives us another foothold into dating the Solar System".
Craters on Earth are quickly eroded, so there are few well preserved impact sites here for scientists to study. But there is little to erase a crater on the Moon except subsequent impacts, so it offers a natural laboratory for understanding how impacts excavate craters and generate pools of molten rock.

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Some of the graphite revealed by the new study appeared in a rare rolled form known as "graphite whiskers," which scientists believe formed in the very high-temperature reactions initiated by a meteorite impact. The discovery also means that the moon potentially holds a record of the carbon input by meteors into the Earth-moon system when life was just beginning to emerge on Earth. The research is published in the July 2 issue of the journal Science.
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Asteroid impacts cause crustal crisis

Asteroids bombarding the Earth triggered major earthquakes that disrupted the evolution of our planet's crust, say Australian researchers.
The research by Dr Andrew Glikson and John Vickers from the Australian National University in Canberra appears in a recent issue of the journal Australian Journal of Earth Sciences.
The researchers say clusters of asteroids tens of kilometres in diameter slammed into the Earth around between 3.47 and 1.85 billion years ago.

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A shift in Jupiter's orbit early in the life of the Solar System dislodged thousands of rocks from the Asteroid Belt, causing them to hit the inner planets, including Earth.
Evidence for this cataclysmic bombardment comes from a reanalysis of lunar rocks brought back by the Apollo astronauts and a careful study of lunar craters, said David Kring, a planetary geologist at the Lunar and Planetary Institute in Houston, Texas.
Kring presented his findings this week at the Geological Society of America's annual meeting in Portland, USA.

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Comet Swarm Delivered Earth's Oceans?
A barrage of comets may have delivered Earth's oceans around 3.85 billion years ago, a new study suggests.
Scientists have long suspected that Earth and its near neighbours were walloped by tens of thousands of impactors during an ancient event known as the Late Heavy Bombardment.

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Comets, not asteroids, to blame for moon's scarred face
Icy comets - not rocky asteroids - launched a dramatic assault on the Earth and moon around 3.85 billion years ago, a new study of ancient rocks in Greenland suggests. The work suggests much of Earth's water could have been brought to the planet by comets.

"We can see craters on the moon's surface with the naked eye, but nobody actually knew what caused them - was it rocks, was it iron, was it ice?  It's exciting to find signs that it was actually ice" - Uffe Gråe Jørgensen, an astronomer at the Niels Bohr Institute in Copenhagen, Denmark.

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Title: The Earth-Moon system during the Late Heavy Bombardment period
Authors: Uffe Graae Jorgensen, Peter W.U. Appel, Yuichi Hatsukawa, Robert Frei, Masumi Oshima, Yosuke Toh, Atsushi Kimura

The Late Heavy Bombardment (LHB) period is the narrow time interval between 3.8 and 3.9 Gyr ago, where the bulk of the craters we see on the Moon formed. Even more craters formed on the Earth.
During a field expedition to the 3.8 Gyr old Isua greenstone belt in Greenland, we sampled three types of metasedimentary rocks, that contain direct traces of the LHB impactors by a seven times enrichment (150 ppt) in iridium compared to present day ocean crust (20 ppt).
We show that this enrichment is in agreement with the lunar cratering rate, providing the impactors were comets, but not if they were asteroids. Our study is a first direct indication of the nature of the LHB impactors, and the first to find an agreement between the LHB lunar cratering rate and the Earth's early geochemical record (and the corresponding lunar record).
The LHB comets that delivered the iridium we see at Isua will at the same time have delivered the equivalent of a km deep ocean, and we explain why one should expect a cometary ocean to become roughly the size of the Earth's present-day ocean, not only in terms of depth but also in terms of the surface area it covers.

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Broken dwarf planet may have scarred the Moon in early solar system
A new analysis of craters of the Moon has suggested that the shattered remnants of a dwarf planet may have bombarded the inner planets in the early solar system.
According to a report in New Scientist, several large impact scars on the moon appear to be around 3.9 billion years old, suggesting that the Earth and other objects of the inner solar system were heavily pounded at that time.
Most astronomers believe that the bombardment was caused by shifts in the orbits of the giant planets, which destabilised the asteroid belt, hurling giant rocks our way.


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The shattered remnants of a dwarf planet may have bombarded the inner planets in the early solar system, suggests a new analysis of craters on the moon.
Several large impact scars on the moon appear to be around 3.9 billion years old, suggesting that the Earth and other objects of the inner solar system were heavily pounded at that time. Most astronomers believe that the bombardment was caused by shifts in the orbits of the giant planets, which destabilised the asteroid belt, hurling giant rocks our way.

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A shower of millions of rocks from space that collided with Mars, the Earth, and the moon about four billion years ago could have warmed our planet and made it wetter, say researchers. Thats what scientists found when they heated ancient rocks like those that hit the Earth billions of years ago and measured the carbon dioxide and water that was released, according to a study published in the journal Geochimica et Cosmochimica Acta.

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