Giant Asteroid Set Earth's Crust in Motion 3 Billion Years Ago



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A dramatic, fresh impact crater dominates this image taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter on Nov. 19, 2013.

Earth was still a violent place shortly after life began, with regular impactors arriving from space. For the first time, scientists have modeled the effects of one such violent event - the strike of a giant asteroid. The effects were so catastrophic that, along with the large earthquakes and tsunamis it created, this asteroid may have also set continents into motion.
The asteroid to blame for this event would have been at least 37km in diameter, which is roughly four times the size of the asteroid that is alleged to have caused the death of dinosaurs. It would have hit the surface of the Earth at the speed of about 72,000kph and created a 500km-wide crater.
At the time of the event, about 3.26 billion years ago, such an impact would have caused 10.8 magnitude earthquakes - roughly 100 times the size of the 2011 Japanese earthquake, which is among the biggest in recent history. The impact would have thrown vaporized rock into the atmosphere, which would have encircled the globe before condensing and falling back to the surface. During the debris re-entry, the temperature of the atmosphere would have increased and 
the heat wave would have caused the upper oceans to boil
the heat wave would have caused the upper oceans to boil.

Donald Lowe and Norman Sleep at Stanford University, who published their research in the journal Geochemistry, Geophysics, Geosystems, were able to say all this based on tiny, spherical rocks found in the Barberton greenstone belt in South Africa. These rocks are the only remnants of the cataclysmic event.
According to Simon Redfern at the University of Cambridge, there are two reasons why Lowe and Sleep were able to do find these rocks. First, the Barberton greenstone belt is located on a craton, which is the oldest and most stable part of the crust. Second, at the time of the event, this area was at the bottom of the ocean with ongoing volcanic activity. The tiny rocks, after having been thrown into the atmosphere, cooling, and falling to the bottom of the ocean, then ended up trapped in the fractures created by volcanic activity.
Impact-diagram

IMAGE: AGU
This impact may have been among the last few major impacts from the Late Heavy Bombardment period between 3 and 4 billion years ago. The evidence of most of these impacts has been lost because of erosion and the movement of the Earth's crust, which recycles the surface over geological time.
However, despite providing such rich details about the impact, Lowe and Sleep are not able to pinpoint the location of the impact. It would be within thousands of kilometres of the Barberton greenstone system, but that is about all they can say. The exact location may not be that important, Lowe argued: "With this study, we are trying to understand the forces that shaped our planet early in its evolution and the environments in which life evolved."
One of the most intriguing suggestions the authors make is that this three-billion-year-old impact may have initiated the the movement of tectonic plates, which created the continents that we observe on the planet.
The continents ride on plates that make up Earth's thin crust; the crust sits on top of the mantle, which is above a core of liquid iron and nickel. The heat trapped in the mantle creates convection, which pushes against the overlying plates.
All the rocky planets in our solar system - Mercury, Venus, Earth and Mars - have the same internal structure. But only Earth's crust shows signs of plate motion.
A possible reason why Earth has moving plates may be to do with the heat trapped in the mantle. Other planets may not have as much heat trapped when they formed, which means the convection may not be strong enough to move the plates.
However, according to Redfern: "Even with a hot mantle you would need something to destabilise the crust." And it is possible that an asteroid impact of this magnitude could have achieved that.


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Archaeologists Find Ancient Puppy Paw Prints on Roman Tiles



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"Archaeologists found Roman tiles with dog paw prints and hoof prints in them."

The paw prints and hoof prints of a few meddlesome animals have been preserved for posterity on ancient Roman tiles recently discovered by archaeologists in England.
"They are beautiful finds, as they represent a snapshot, a single moment in history," said Nick Daffern, a senior project manager with Wardell Armstrong Archaeology. "It is lovely to imagine some irate person chasing a dog or some other animal away from their freshly made tiles."
The artifacts, which could be nearly 2,000 years old, were found in the Blackfriars area of Leicester, the English city where the long-lost bones of King Richard III were discovered under a parking lot in 2012. Wardell Armstrong Archaeology was brought in to dig at a site where a construction company plans to build student housing.

At least one of the tiles is tainted with dog paw prints, and one is marked with the hoof prints of a sheep or a goat that trampled on the clay before it was dry.
"My initial thought was that it must have been very difficult being a Roman tile manufacturer with these animal incursions going on all the time," Philip Briggs, another Wardell Armstrong archaeologist, told Live Science in an email.
The tiles were found in layers of rubble that had been laid down as a hard base for subsequent floors, but the artifacts' original context is unclear, Daffern said.
"We don't know if the tiles were originally part of an earlier building or were bought in from elsewhere specifically to raise and stabilize ground," Daffern told Live Science in an email.
Leicester was the stronghold of an Iron Age group known as the Corieltauvi tribe, and it remained an important city after the Roman conquest of Britain in the first century A.D., as it was located along the Fosse Way, a Roman road that connected southwestern England with the East Midlands.
The excavators say that, in addition to the animal-printed tiles, they've uncovered Roman tweezers, brooches, coins and painted wall plaster. They've also unearthed traces of a large Roman building — perhaps a basilica, with a peristyle, or columned porch — that was largely robbed of its masonry during the medieval era for other construction projects.
The archaeologists even discovered late Iron Age artifacts, such as several fragments of clay molds that the Corieltauvi tribe likely used to make coins before the Roman rule. Daffern said it's rare to find sites with coin molds, given how closely managed coin production would have been during the Iron Age.
"I think the excavation thus far has significantly multiplied the number of coin mold fragments recovered from Leicester, probably by approximately tenfold," Daffern said in an email.
The excavation is funded by construction company Watkin Jones. The archaeologists are providing updates on Wardell Armstrong Archaeology's blog.


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Shonda Rhimes Shares 'Scandal' Blooper Reel After Bonkers Season 3 Finale



Spoiler alert: This post contains spoilers for season three, episode 18 ofScandal. If you have not watched the episode, stop reading now.

Season three of Scandal wrapped up with an election-altering church explosion, a surprise death (maybe even two, depending on how Harrison's cliffhanger moment unfolds) and Olivia's decision to fly away from the nation's capital with Jake by her side.
Show creator Shonda Rhimes joined late-night host Jimmy Kimmel to discuss the finale and share the above blooper reel, with an assist from actor Scott Foley.

The behind-the-scenes gaffes teach us Mellie (Bellamy Young) can't stop saying "fart" in place of more jarring expletives, Huck (Guillermo Díaz) is an expert Shake Weight user, Harrison (Columbus Short) can control his pecs quite well and David (Joshua Malina) loves teasing Jake (Foley) about his Felicity days at inopportune times.
Rhimes also fielded several questions about the season's last episode, "The Price of Free and Fair Election." Rhimes gives insight into whether Olivia (Kerry Washington) really quit Olivia Pope & Associates, how Jake almost became a vice-presidential candidate instead of B613's leader as well as what the thought process was for Huck and Quinn's sex scene.

In another segment, Rhimes answers questions about Harrison's fate (is he dead?).

A third clip recaps the cast's individual visits to Jimmy Kimmel Live!

Kimmel, in a final video, interviews a not-so-anonymous informant.


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