New research from the National Aeronautics and Space Administration shows the earth's earliest rocks and outer crust were likely lost to giant asteroids.
Findings by an international team of researchers show the planet's face around four billion years ago went through an extreme makeover, after the still-young world suffered a series of collisions with asteroids that left its surface melted, mixed, and buried.
The new so-called terrestrial bombardment model suggests the role asteroid collisions played in the evolution of the uppermost layers of the early Earth was greater that previously figured during the geologic eon called the "Hadean," an estimated 4 to 4.5 billion years ago.
The new conclusions are included in a paper, "Widespread Mixing and Burial of Earth's Hadean Crust by Asteroid Impacts," published in the July 31, 2014 issue of the journal Nature.
"A large asteroid impact could have buried a substantial amount of Earth's crust with impact-generated melt," said Yvonne Pendleton, director of the space agency's Solar System Exploration Research Virtual Institute in California. "This new model helps explain how repeated asteroid impacts may have buried Earth's earliest and oldest rocks."
Researchers say Earth went through a sequence of major growth phases: the initial accumulation over tens of millions of years of planetessimals and other matter into a larger body that eventually became the earth; an impact with a large proto-planet that resulted in the the formation of the moon; periodic bombardment from huge asteroids several tens to hundreds of miles in size , far bigger than the one scientists believe led to the extinction of the dinosaurs 65 million years ago.
The new data 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 the planet.
"Prior to approximately four billion years ago, no large region of Earth's surface could have survived untouched by impacts and their effects," said Simone Marchi, SSERVI senior researcher at the Southwest Research Institute in Boulder, Colorado, and the paper's lead author. "The new picture of the Hadean Earth emerging from this work has important implications for its habitability."
Large impacts, said the NASA release, had particularly severe effects on existing ecosystems. Researchers found on average that Earth more than four billion years ago could have undergone enough large impact collisions to cause global sterilization, as well as the vaporization of all the planet's oceans.
"During that time, the lag between major collisions was long enough to allow intervals of more clement conditions, at least on a local scale," said Marchi. "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."
