A team of scientists from France, Germany and the US—in their study whose findings have been published in Nature—have estimated that the Earth’s only natural satellite was born 95 million years after the solar system came into being. The Moon was formed after a protoplanet, Theia, crashed into the Earth and sent debris flying into space which subsequently coalesced—this explains why our planet and its nearest celestial neighbour are so ‘atomically identical’ in their isotope content.
All previous attempts at setting a geologic timeline for the solar system have been based on different radiometric dating methods, including some that throw up very unreliable findings—estimates have ranged between 30 million years and 100 million years after the birth of the solar system. However, this time, the scientists used 259 computer simulations of the protoplanetary disk, the band of rocky matter that later made up the four terrestrial planets—Mercury, Venus, Earth and Mars. They measured the siderophile (elements such as gold, platinum and iridium that dissolve in molten iron) content on the Earth before the Theia impact, after the Moon-forming event and today, to arrive at the Moon’s age. This method relies on the well-supported theory that the Theia impact caused siderophiles to sink into Earth’s iron-rich core from the crust. Given that crust was completely stripped of the siderophiles, whatever of these rare metals is found today in the Earth’s crust must have come from later impacts. How is the study significant? It helps discern which radiometric dating methods are reliable given that some had pegged the age of the Moon close to the new method’s figure.