Tuzo and Jason are two of Earth’s lesser-known continents.
It’s not surprising that more people haven’t heard of them. They were only discovered beginning in the 1980s. And nobody has visited either of them in person. They lie deep inside the planet, at the bottom of the silicate-rich mantle, above the iron-nickel core. They are more or less opposite one another. Tuzo (named after earth scientist Tuzo Wilson) lies underneath southern Africa, stretching out on either side into Atlantic and Indian Oceans. Jason (named after W. Jason Morgan) lies underneath the mid-Pacific Ocean. They are huge, about 6% of the whole volume of the Earth. Each extends thousands of kilometers laterally, and is hundreds of kilometers in height.
OK, the scientifically approved name for them is not “continents,” but LLSVPs, Large Low-Shear-Velocity Provinces, reflecting the fact that they were detected by measuring variation in the speed at which shear waves from earthquakes travel through the Earth. They seem to have fairly sharp boundaries, which implies they are not just regions of higher-than-average temperature, but actually have a different composition than the rest of the mantle: you can think of them as “continents” in other words, with the mantle around them as a slow stony “atmosphere”.
Where did they come from? One theory is that they are made up of material from the upper reaches of the mantle, from oceanic slabs, that drifted down and piled up at the bottom. There’s a more dramatic theory however: It may be that these subterranean continents are remnants of the planet Theia. When Theia crashed into the young Earth 4.6 billion years ago, the collision sent a blast of rock into orbit that eventually coalesced into the Moon. But Tuzo and Jason may be a portion of Theia’s mantle, different in composition and denser than Earth’s mantle.
Logarithmic History 