A small planet collided with a young Earth 4.5 billion years ago, sending molten rock into space. Most scientists believe that this lava cooled and solidified over time, resulting in the moon.
However, this is “more of a choose-your-own-adventure novel,” according to a new article published in the journal Nature Geoscience this week.
The newborn moon was “out of equilibrium” deeper beneath the surface
The majority of what we know about the moon is based on the analysis of rock samples taken by Apollo astronauts over 50 years ago, as well as theoretical models. Samples of basaltic lava rocks acquired from the moon have remarkably high levels of titanium. Satellite observations later revealed that these titanium-rich volcanic rocks are mostly found on the moon’s nearside, but until recently, we had no idea how they got there.
The moon formed hot, which indicates that it was most likely covered by a global magma ocean. As this molten rock cooled and hardened, it formed the moon’s mantle and bright crust, which is what we see when we gaze at it.
However, the newborn moon was “out of equilibrium” deeper beneath the surface. New models show that fragments of the magma ocean crystallized into dense minerals like ilmenite, which includes titanium and iron.
“Because these heavy minerals are denser than the mantle underneath, it creates a gravitational instability, and you would expect this layer to sink deeper into the moon’s interior,” said Weigang Liang, who led the research, in a press statement.
However, over time, this dense material sank into the interior, mixed with the mantle, melted, and returned to the surface as titanium-rich lava flows, similar to those seen on the surface of the Moon.
“Our moon literally turned itself inside out. But there has been little physical evidence to shed light on the exact sequence of events during this critical phase of lunar history, and there is a lot of disagreement in the details of what went down – literally,” said co-author Jeff Andrews-Hanna, in a press statement.