For decades, planetary scientists have been trying to understand the origins of two colossal geological anomalies inside our planet. New insights suggest they could be leftovers from a cosmic collision
OUR planet is like a bad cake in a cosmic baking contest. On inspection of the first slice, the judges might say its layering is quite neat. The crunchy crust sits on a solid-but-squidgy mantle, which wraps around a gooey outer core. But cut another slice and they will soon see that something has gone awry. Looming inside the neat layers are two giant, messy lumps.
These two blobs are colossal. They are the size of continents, covering almost a third of the boundary between the core and the mantle. We also know that they are hotter than their surroundings. But everything else about these blobs is mysterious, from what they are made of and where they came from to how they affect our planet today.
The quest to understand them has so far verged on the quixotic. Geologists and planetary scientists are pursuing it with vigour, however, because the blobs are likely to be guarding some serious secrets. We are scrambling to get a better picture of these shadowy underworld titans, not least how ancient they are.
That is important because if they turn out to be geologically youthful, it would suggest we are living through a special epoch. There must be something particularly strange going on down there, to produce such giant oddities. Whereas “if these things are truly ancient”, says Sujoy Mukhopadhyay at the University of California, Davis, “it tells us something about how our planet formed”. And they might even surprise us with an answer to a bigger question, one that goes beyond parochial concerns about our own planet.
Since the late 19th century, geologists have …