Early Earth had Violent Encounters With Giant Asteroids

In case you need a reminder that the solar system was a harsh place to grow up, the early Earth looks like it was in the middle of a shooting gallery. Asteroids and comets that repeatedly smashed into the early Earth covered the planet’s surface with molten rock during its earliest days.

New research shows that more than four billion years ago the surface of Earth was heavily reprocessed – or melted, mixed, and buried – as a result of giant asteroid impacts.

A new terrestrial bombardment model, calibrated using existing lunar and terrestrial data, sheds light on the role asteroid collisions played in the evolution of the uppermost layers of the early Earth during the geologic eon called the “Hadean” (approximately 4 to 4.5 billion years ago).

An international team of researchers from academic and government institutions, including NASA’s Solar System Exploration Research Virtual Institute (SSERVI) at NASA’s Ames Research Center in Moffett Field, California, published their findings in the July 31, 2014 issue of Nature.

 Earth formed about 4.5 billion years ago. The first 500 million years of its life are known as the Hadean Eon. Although this time amounts to more than 10 percent of Earth’s history, little is known about it, since few rocks are known that are older than 3.8 billion years old.

For much of the Hadean, Earth and its sister worlds in the inner solar system were pummeled with an extraordinary number of cosmic impacts.

“It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish,” said lead study author Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.

“The new picture of the Hadean Earth emerging from this work has important implications for its habitability,” added Marchi, who is also senior researcher at NASA’s Solar System Exploration Research Virtual Institute.

In this dangerous early period, the researchers estimate the Earth was smacked by 1-4 asteroids or comets that were more than 600 miles (966 kilometers) wide — enough to wipe out life across the planet. They also believe that between 3-7 impactors were more than 300 miles (482 kilometers) wide, which would evaporate oceans across the world.

 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.”

The research was an international effort led by Marchi and William Bottke from the Southwest Research Institute in Boulder; Linda Elkins-Tanton from Carnegie Institution for Science in Washington; Michael Bierhaus and Kai Wünnemann from the Museum fur Naturkunde in Berlin, Germany; Alessandro Morbidelli from Observatoire de la Côte d’Azur in Nice, France, and David Kring from the Universities Space Research Association and Lunar and Planetary Institute in Houston.

The research was supported in part by SSERVI, a virtual institute that, with international partnerships, brings science and exploration researchers together in a collaborative virtual setting.

Source: https://goo.gl/K0J4fx