A 466-million-year-old space collision is still raining shrapnel on Earth (WaPo)

By Sarah Kaplan
January 23

Roughly 466 million years ago, something huge exploded in space and sent shrapnel raining down on Earth.

It was the biggest such cataclysm to happen in our celestial neighborhood in some 3 billion years. An asteroid belt body, roughly as large as Connecticut and made of some of the most ancient material in the solar system, collided with another object and splintered into pieces. Those pieces in turn slammed into one another, creating more debris. One by one, the fragments fell toward ancient Earth, where the continents were clumped into a single, gigantic mass called Gondwana and the very first terrestrial plants were just beginning to creep onto land. At the time, those meteorites, called L chondrites, made up 99 percent of all space rocks that landed on our planet.

Millennia passed, the continents broke apart and bunched back together, mountain ranges rose up and eroded away, countless creatures — trilobites, dinosaurs, woolly mammoths — evolved and went extinct. But the debris from that 466-million-year-old breakup continued to fall. And fall. And fall. Even now, they make up the largest group of meteorites that land on Earth.

“That collision cascade” — the series of smaller smashes and crashes that followed the initial breakup — “had consequences that are still felt today,” said Philipp Heck, a cosmochemist at the University of Chicago and curator of meteorites for the Field Museum.
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more: https://www.washingtonpost.com/news/speaking-of-science/wp/2017/01/23/a-466-million-year-old-space-collision-is-still-raining-shrapnel-down-on-earth/?utm_term=.4c3573c3d342
full paper: http://www.nature.com/articles/s41550-016-0035