Moon’s explosive birth drove iron deep into Earth’s core

Our moon was made by the Big Splash, an impact that we thought left iron deposits near Earth’s crust. It turns out that the metal sank into our planet’s core

Leftovers from the moon’s formation may have tunnelled to the Earth’s core, and make up far more of our planet than we once thought.

According to earlier estimates about 0.5 per cent of our planet’s mass came from swallowing parts of planetesimals, 1000-kilometres across, just after the “Big Splash” that formed the moon. Now, simulations by researchers at the Southwest Research Institute (SWRI) in Boulder and the University of Maryland have upped that percentage to between 1 and 2.5 per cent.

That may not sound like much, but it helps explain something odd about the mantle, the part of Earth’s interior between the crust and the core. Earth’s mantle has a lot of siderophile elements, metals with a chemical affinity for iron. That is unexpected since iron should sink to the Earth’s core.

“We realised that there are many cases where the core of the impactor does not end up being well mixed