Recent analysis of several lunar craters suggests that the Earth-Moon system suffered a particularly violent bombing episode 800 million years ago.
Between 40 and 50 trillion metric tons of meteorites descended on the Earth-Moon system 800 million years ago, study finds. It was 30 to 60 times the amount of material involved in the Chicxulub impact that precipitated the demise of non-avian dinosaurs 66 million years ago.
Our planet shows almost no sign of this trauma. The scars of this attack from above have long been erased by erosion, volcanism and other geological processes. In fact, virtually all traces of ground bombardments that took place over 600 million years ago are no longer available. On the other hand, the Moon still bears some marks of it.
In recent work, published in the journal Nature communication, researchers at Osaka University (Japan) analyzed data from the Kaguya lunar orbiter, from the Japanese Space Agency (JAXA). The team focused on studying 59 craters over 20 kilometers in diameter.
Specifically, it was to estimate the age of formation of these large craters by examining the density of craters 0.1 to 1 km in diameter in their ejecta. Among them was the Copernicus crater (93 km in diameter) and its 860 small surrounding craters. The density of the latter thus made it possible to determine the age of the largest crater.
A violent meteor shower
Out of this sample of 59 craters, the researchers determined that eight of them formed simultaneously about 800 million years ago.
Computer simulations attempting to reproduce these different impacts suggest that the culprit is none other than a gigantic asteroid 100 kilometers wide, some fragments of which have rained on the Moon. Others escaped this first obstacle, before finally crashing into Earth.
Obviously, not all of them have been around our nearby system. Some probably ended their course in the Sun, while others wisely remained in the asteroid belt, between the orbits of Mars and Jupiter.
In addition, further analysis showed that the parent asteroid belonged to the Eulalia asteroid family. The asteroid Ryugu, a sample of which is currently on its way back to Earth, is said to be part of the same family. Moreover, it would not be impossible for the latter to be itself a fragment of this first parent asteroid.
If this study is to be believed, these cosmic impacts would therefore have struck the Earth and the Moon just before the cryogenic period, which extends from -720 million to -635 million years. It was during this time that our planet suffered its greatest ice ages. So it’s not impossible that this cosmic bombardment has something to do with it.
Previous research had indeed suggested that the Chicxulub impact 66 million years ago released such a large amount of dust into the atmosphere that the sky darkened, ultimately cooling the Earth.
We also know that 470 million years ago, another meteor shower also stirred up extraordinary amounts of dust, potentially triggering the Middle Ordovician Ice Age. However, this episode was probably much less impressive than the event experienced 800 million years ago.