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NASA - Asteroid Bombardment - 4.5-3.5 Gyr ago

NASA simulation shows the heavy pummeling ancient Earth took from massive asteroids

Scott Sutherland
Meteorologist/Science Writer

Friday, August 1, 2014, 12:29 PM - Have you ever heard of the Late Heavy Bombardment? This period in our planet's history - roughly four billion years ago - has an ominous name attached to it, but the full impact of this event (if you'll pardon the pun) is hard to grasp until you watch the above simulation, put together by scientists working with NASA's Ames Research Center.

Although there are only a few obvious impact craters left here on Earth - Meteor crater in Arizona and Manicouagan crater in Quebec are good examples - we only need to look up into the night sky, to the face of the moon, to see evidence that our planet has suffered many more impacts than that during its 4.5 billion-year-long history. The only reason Earth doesn't show this same kind of scarring is due to the action of the atmosphere and water to erode the landscape, not to mention the movement of the various tectonic plates that slip and slide around on the surface. However, during that period of 4.5-3.5 billion years ago, it was this pummeling by large asteroids that shaped the face of the planet

"A large asteroid impact could have buried a substantial amount of Earth’s crust with impact-generated melt," Yvonne Pendleton, the director of the NASA’s Solar System Exploration Research Virtual Institute (SSERVI) at Ames Research Center, said in a NASA statement. "This new model helps explain how repeated asteroid impacts may have buried Earth's earliest and oldest rocks."

Much later in Earth's timeline, when there was abundant life around, asteroid impacts were killers, as any dinosaurs could easily confirm (if any were still alive to tell the tale). However, at that ancient time, known as the Hadeon eon, these impacts would have dictated exactly what kind of life was going to develop on the planet.

Artist's conception of early Earth, showing a surface
pummeled by large impacts.
Credit: Simone Marchi/Southwest Research Institute

"Prior to approximately four billion years ago, no large region of Earth's surface could have survived untouched by impacts and their effects," lead researcher Simone Marchi, SSERVI senior researcher at the Southwest Research Institute in Boulder, said in the statement. "The new picture of the Hadean Earth emerging from this work has important implications for its habitability."

One thing that is evident from the simulation is that early life would have had to be very hardy to persist. While the asteroid that finished off the dinosaurs was thought to be only around 10 km wide, according to the researchers, early Earth may have been hit by anywhere between one and four asteroids - somewhere around 1000 km wide each - which would have been capable of completely sterilizing the planet. There could have been another three to seven 'impactors' that would have measured at least 500 km wide each, which would have completely vapourized Earth's oceans upon impact. However, life on Earth wasn't completely wiped out (evidenced, at the very least, by the fact that we're here to contemplate all this), and the researchers have their thoughts on what it would have taken to survive.

"During that time, the lag between major collisions was long enough to allow intervals of more clement conditions, at least on a local scale," Marchi said. "Any life emerging during the Hadean eon likely needed to be resistant to high temperatures, and could have survived such a violent period in Earth's history by thriving in niches deep underground or in the ocean's crust."

According to the statement: "Researchers estimate accretion during the late bombardment contributed less than one percent of Earth’s present-day mass, but the giant asteroid impacts still had a profound effect on the geological evolution of early Earth. Prior to four billion years ago Earth was resurfaced over and over by voluminous impact-generated melt. Furthermore, large collisions as late as about four billion years ago may have repeatedly boiled away existing oceans into steamy atmospheres. Despite the heavy bombardment, the findings are compatible with the claim of liquid water on Earth’s surface as early as about 4.3 billion years ago based on geochemical data. The new research reveals that asteroidal collisions not only severely altered the geology of the Hadean eon Earth, but likely also played a major role in the subsequent evolution of life on Earth as well."

The research on this was published on Thursday in the journal Nature (click here).

(H/T to Elizabeth Howell at Universe Today)

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