Moon Gets a New Birthday Formation happened later than thought, study says By Rob Quinn, Newser Staff Posted Apr 3, 2014 1:36 AM CDT 13 comments Comments The moon is made up of parts of the asteroid and early Earth. (AP Photo/Kin Cheung) (Newser) – The cataclysmic event that formed the moon happened much later than previously believed, according to researchers who have shifted the satellite's "birthday" forward around 60 million years. New computer simulations and analysis of elements in the Earth's crust suggest that the moon formed 95 million years after the birth of the solar system, when a Mars-sized asteroid smashed into our still-forming planet, sending debris into space that coalesced into the moon, National Geographic reports. "Earth was put together piece by piece. It didn’t just appear all at once. And the last piece was probably when something the size of Mars—about 10% of Earth’s mass—hit Earth," astrophysicist John Chambers tells Discovery. "Most of that material stayed on Earth, but some of it got blown into space, along with some stuff from Earth, and that then coalesced to form the moon." The findings suggest that Earth wasn't fully formed until 100 million years after the birth of the solar system, while Mars was formed in just a few million years, Reuters notes.