From Rebecca Boyle at Quanta:
Textbooks say that the moon was formed after a Mars-size mass smashed the young Earth. But new evidence has cast doubt on that story, leaving researchers to dream up new ways to get a giant rock into orbit.
In the past five years, a bombardment of studies has exposed a problem: The canonical giant impact hypothesis rests on assumptions that do not match the evidence. If Theia hit Earth and later formed the moon, the moon should be made of Theia-type material. But the moon does not look like Theia — or like Mars, for that matter. Down to its atoms, it looks almost exactly like Earth.
Confronted with this discrepancy, lunar researchers have sought new ideas for understanding how the moon came to be. More.
With so much uncertainty about textbook truths, let’s hope that this field is not assailed, as evolution is, by the Tone Deaf, whose mission is to Stamp Out Doubt and whose likely success will consist of convincing people that truth is not to be had anywhere.
Space.com: Scientists finally know how old Moon is What’s surprising, really, is how little we know about the moon in general.
Another moon origin theory: Epic crash
How the Moon Formed: 5 Wild Lunar Theories (Mike Wall at Space.com, 2014)
Our moon formed in collision with embryo planet?
Origin of the moon still shrouded in mystery