What lies deep in the mantle below?

Deep within Earth's interior, in the brittle lithosphere and in the viscous asthenosphere below it, magma collects and ultimately feeds erupting volcanoes on Earth's surface. This magma holds keys to understanding the processes that create island chains like Hawaii. However, scientists can map the mantle--or any part of Earth's interior--only by using remote sensing techniques. The most important such technique is seismic tomography. Similar to medical computerized tomography (CT) scanning, seismic tomography allows scientists to construct three-dimensional images of deep Earth from observations of seismic waves that have passed through it. The speed of these waves varies depending on the composition, phase, temperature, and pressure of the material through which they travel. Analyzing seismic waves can thus reveal details of these deep materials. Were it not for seismology, we would be almost totally ignorant of the structure of the deep interior of Earth. The term "seismic tomography" was first coined by Adam Dziewonski and Don L. Anderson [Dziewonski and Anderson, 1984]. Over subsequent decades, the method has received substantial research funding, and the results have profoundly influenced our knowledge of Earth's structure and dynamics. Nevertheless, communicating the technique's limitations between subdisciplines within Earth science remains a challenge. For reasons of space and other factors, published papers often tend to deemphasize important caveats [Foulger et al., 2013]. The bottom line is that scientists tend to underestimate pitfalls and often have disproportionate faith in results.