The revised timing of the impact implies the terrestrial planets, such as the Earth and Mars, took longer to build up from the collision of smaller 'planetesimals' than previously thought. "The age of the Moon is also the age of Earth because the Moon-forming giant impact was the last major event in Earth's formation," says Touboul.
Alan Brandon, a scientist at NASA's Johnson Space Center in Houston, Texas, US, agrees. "It may mean that Earth and Mars took at least 50 million years, and possibly hundreds of millions of years, to reach their final mass," he comments.
The researchers also found that the composition of the Moon appears identical to that of the Earth's rocky mantle, "such that a major portion of the Moon must have been from proto-Earth", Brandon told New Scientist.