Geologic 'Clock' Shows Moon Formed Roughly 100 Million Years after Solar System's Birth

An international team of researchers says that the moon is around 4.47 billion years old. Researchers used a "geological clock" and found that the Earth's satellite formed roughly 100 million years after the birth of the solar system. An important feature of the current study is that researchers did not rely on radioactive decay of elements (such as uranium), which is how other researchers have been estimating the moon's age. For the study, researchers used measurements from the core of the Earth along with computer simulations of protoplanetary disk from which terrestrial planets formed. "We were excited to find a 'clock' for the formation time of the Moon that didn't rely on radiometric dating methods. This correlation just jumped out of the simulations and held in each set of old simulations we looked at," said  Seth Jacobson of the Observatory de la Cote d'Azur in Nice, France lead author of the study. A long-held theory about moon formation suggests that a giant object called Theia hit infant earth. The object was about the size of Mars and debris from this impact formed the moon. According to other researchers, Earth gained weight after this giant impact. Jacobson and team analyzed 259 simulations of the growth of rocky planets and found a relationship between the time of the early impact and the amount of weight gained by Earth. The present study rests on the idea that the collision brought iron-loving elements such as platinum or iridium to the planet, National Geographic reported. "When the moon-forming event occurs, this melts the entire surface of the Earth," Jacobson told National Geographic. The iron at the surface of the earth sunk to the center and took the siderophile elements with it. The new "clock" uses these geochemical measurements to date moon's birth to some 95 ±32 million years after the birth of the solar system. According to the researchers, the new estimate agrees with results of some radioactive dating analysis. The study also shows that the birth of the solar system was quite violent with several objects hitting new-born planets. "This result is exciting because in the same simulations that can successfully form Mars in only 2 to 5 million years, we can also form the Moon at 100 million years. These vastly different timescales have been very hard to capture in simulations," said author Dr. Kevin Walsh from the Southwest Research Institute (SwRI) Space Science and Engineering Division, according to a news release. The study is published in the journal Nature. The research was funded by European Research Council, as well as NASA's Astrobiology Virtual Planetary Laboratory, Planetary Geology and Geophysics, Lunar Science Institute and Solar System Exploration Research Virtual Institute programs.