Hank: So you know how in school you learn that the Earth looks like this, [cutaway image of Earth with three concentric layers] - it doesn't. It looks like this. [rotating Earth image of three concentric layers with irregular shapes in mantle] See those two blobs? They are sometimes called mantle blobs; they are larger than continents. And if they were on the surface of the planet, they would be so tall the International Space Station would have to steer around them.

These blobs might be old piles of the Earth's crust, it might be something left over from the Earth's 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, others think they may have powered super volcanoes.

To know for sure, we need to know what the blobs are made of, and we don't. We just know they're there. 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.

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