Lunar craters suggest Earth, Moon may have witnessed asteroid shower 800 million years ago: Study
A new study suggests that about 800 million years ago, right before the Cryogenian period — a time when icy deserts dominated the Earth — our planet and the Moon witnessed an asteroid shower. The Earth has no record of the event. But its companion, the lunar body, has preserved it in their craters. Impact craters form when an asteroid or a comet falls into a planet or moon, creating a large hole as a result. "In this study, we used the Moon as 'a witness to the history of the solar system', because the moon surface has no erosion and well preserves the impact history of the Earth-Moon system," Dr Kentaro Terada, the lead author and professor at Osaka University, told MEA WorldWide (MEAWW). "This is a 'quite new idea', shedding light on the veiled impact history of the Earth before 600 million years," he added.
Asteroids play a part in shaping the Earth. For instance, a massive asteroid hit the planet 66 million years ago. The incident, dubbed Chicxulub impact, is linked to mass extinction in which more than three-fourths of all plant and animal species were wiped out of existence. The impact raised temperatures, causing global warming. Further, some researchers think asteroids may have carried phosphorus — an element essential to life forms — to Earth. In this study, researchers analyzed data collected from Terrain Camera on Kaguya, a Japanese Space Agency's lunar orbiter spacecraft. In all, they studied 59 lunar craters with a diameter of approximately 20km. They estimated that 8 of them were formed at the same time, about 800 million years ago. This suggests an asteroid shower on the whole Moon, explained Terada. It also implies that the Earth witnessed the same event.
(Osaka University)
But what caused the shower about 800 million years ago? According to Terada, a parent asteroid of 100km diameter may have disintegrated after a collision. He added that the event is likely to have sent at least (4-5)×10^16kg of meteoroids, nearly 30-60 times more than the Chicxulub impact, to Earth immediately before the Cryogenian. The period lasted between 720 and 635 million years ago. They also suspect that the parent body was a C-type asteroid, Eulalia. The C-type asteroids are those that contain carbon elements. Following the disruption of the parent asteroid, some of the resulting fragments fell on terrestrial planets and the Sun. Some could have stayed in the asteroid belt between Mars and Jupiter. Others may have become near-Earth asteroids.
The shower may have brought the crucial life-forming element to Earth. "Our new finding suggests that approximately 10^14kg of extra-terrestrial phosphorus should have accumulated across the Earth 800 million years ago, which is one order of magnitude higher than the total phosphorus amount of the modern sea," Terada said. Estimating the age of lunar crater provides new insights on the impact of asteroids on climate and its role in driving ecosystems towards larger and increasingly complex organisms after 800 million years. But the topic needs more investigation, he added.
The study is published in Nature Communications.