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Something mysterious happened nearly half a billion years ago that triggered one of the most important changes in the history of life on Earth. Suddenly, there was an explosion of species, with the biodiversity of invertebrate animals increasing from a very low level to something similar to what we see today. The most popular explanation for this "Great Ordovician Biodiversification Event" is that it was a result of an uncomfortably hot Earth cooling and eventually heading into an ice age.
But what actually triggered the change in temperature? In our new paper, published in Science Advances, we show that its onset coincided exactly with the largest documented asteroid breakup in the asteroid belt during the past two billion years, caused by a collision with another asteroid or a comet. Even today, almost a third of all meteorites falling on Earth originate from the breakup of this 150 kilometer-wide asteroid between Jupiter and Mars.
Event - Amounts - Dust - System - Effect
Following this event, enormous amounts of dust would have spread through the solar system. The blocking effect of this dust could have partly stopped sunlight from reaching the Earth—leading to cooler temperatures. We know that this involved the climate changing from being more or less homogeneous to becoming divided into climate zones—from Arctic conditions at the poles to tropical conditions at the equator. The high diversity among invertebrates, including green algae, primitive fish, cephalopods and corals, came as an adaptation to the new climate.
Our evidence comes from detailed studies of sea floor sediments of Ordovician age (485m-443m years ago) exposed at Kinnekulle in southern Sweden and Lynna River near St. Petersburg in Russia. In a quarry at Kinnekulle, we found more than 130 "fossil meteorites"—rocks that fell on Earth in the ancient past, which became embedded in sea floor sediments and were preserved just like animal fossils.
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