So you know how in school we learn that the Earth looks like one thing? Well, it doesn’t. It looks like this: two gigantic blobs, sometimes called mantle blobs, that are larger than continents. If they were on the surface of the planet they would be so tall that the International Space Station would have to steer around them.
These blobs might be old piles of the Earth’s crust, or something left over from its formation. We know they’re there because seismic waves from earthquakes travel through them differently.
Some researchers think the blobs might fuel Hot Spot volcanoes like the ones in Hawaii, while others think they may have powered super volcanoes. To know for sure, we need to know what the blobs are made of, but we don’t. Seismic wave studies haven’t been that conclusive, so for now all we know is that they’re there, just messing with our conceptions of what the planet is.