The Moon experienced a bombardment by meteoroids (small asteroids) approximately 800 million years ago, suggests a paper published in Nature Communications. Based on collision probabilities, the research suggests that meteroids with a total mass of approximately 30 to 60 times that of the meteorite responsible for the Chicxulub impact collided with the Earth just prior to the Cryogenian period (approximately 720 to 635 million years ago).
Erosion and resurfacing processes on Earth make it difficult to study and date ancient meteoroid impacts. However, an alternative approach to understanding these impacts is to study craters on the Moon, where the effects of weathering and erosion are greatly reduced.
Using data from the lunar orbiter Kaguya, Kentaro Terada and colleagues estimated the formation ages of 59 craters with diameters larger than 20km on the Moon’s surface. The authors found that eight of these craters were formed simultaneously, including the Copernicus crater. Based on radiometric dating of ejected material from the Copernicus crater and data obtained from impact glass spherules (glassy beads formed by meteorite impacts) from some of the Apollo missions, they conclude that the Moon experienced an asteroid shower approximately 800 million years ago. The authors assume that as an asteroid shower took place on the Moon, a similar event must have occurred on Earth. Using crater-scaling laws and collision probabilities, they suggest that an asteroid mass of 40 million billion to 50 million billion kilograms collided with the Earth.
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