Scientists have discovered an anomalous blob of heat on the far side of the moon.
This mysterious hotspot has a strange origin: It’s likely caused by the natural radiation emanating from a huge buried mass of granite, which is rarely found in large quantities outside of Earth, according to new research. On the moon, a dead volcano that hasn’t erupted for 3.5 billion years is likely the source of this unusual hunk of granite.
As someone else already commented, the leading theory since several decades (all other theories about the origin of Earth’s moon fell by the wayside once we went to the moon and brought back moon rocks for analysis) is that Proto-Earth collided with a roughly Mars-sized object we’re calling Theia. As a result, the material from both was mixed. Part of that mix of two (proto-)planets got ejected and formed the moon, while the rest formed the Earth (with smaller objects forming temporarily in unstable orbits and raining down as meteorites on both the Earth and the Moon).
Here’s a Wikipedia article on the topic
Some podcast I was listening to was saying something to the effect that one of the reasons we have such a diverse mix of elements close enough to the surface to easily mine was thought to be due to that collision. Interesting stuff.