The biggest collision on the Moon was more than 4 billion years ago

Scientists at the University of Manchester date the South Pole-Aitken basin on the Moon to between 4.32 and 4.33 billion years ago.

The Moon is littered with impact craters from the constant bombardment of asteroids and comets over billions of years. The South Pole-Aitken Basin (SPA) is the largest and oldest known impact site on the Moon, stretching nearly 2,000km on the far side of the Moon.

Elevation data shows the Moon's South Pole-Aitken Basin, the largest and oldest impact basin on the Moon, in blue and purple. (Image: NASA/GSFC/University of Arizona).

Scientists at the University of Manchester analyzed the lunar meteorite Northwest Africa 2995 , found in Algeria in 2005. The meteorite contains uranium and lead dating back to this period. The study was published in the journal Nature Astronomy on October 16.

The proposed age of the SPA basin is around 120 million years older than expected. 'For decades, it has been agreed that the most intense period of bombardment was concentrated around 4.2-3.8 billion years ago,' said Dr Joshua Snape, a research fellow at the University of Manchester. 'However, the dating of the South Pole-Aitken basin to be 120 million years earlier undermines this argument. This suggests a more gradual collisional process over a longer period of time .'

The discovery also has implications for Earth's early history. The Earth and Moon may have experienced similar impacts in their early history, but the rock record from Earth has been lost, says Dr Romain Tartese, senior lecturer at the University of Manchester. We can use what we have learned about the Moon to provide clues about conditions on Earth during the same time period.

While dating from the Northwest Africa 2995 meteorite has provided a good indication of the age of the SPA basin, the team will have to confirm this data with a mission to retrieve samples from inside the crater.