I read a recent article in Science, summarized here (http://science.sciencemag.org/content/349/6252/1032.short http://science.sciencemag.org/content/349/6252/10

I read a recent article in Science, summarized here (http://science.sciencemag.org/content/349/6252/1032.short http://science.sciencemag.org/content/349/6252/1032.short), on tomographic analysis of Earth's mantle using data recovered during large earthquakes. The large plumes that, for example, create volcanic islands like Hawaii turn out to be ~600km wide, and extend to ~3000 km below the surface. It was not known previously how deep these plumes go. Many thought they were much smaller and shallower. It's in some sense surprising that even basic facts like this are the current frontier.