CURATED BLOCKED QUESTION

A direct sample of the Earth's lower mantle

Everything known about the lower mantle is inferred from seismology, xenoliths and high-pressure experiments. The deepest borehole ever drilled, the Kola Superdeep, reached about 12 km — still within the crust. Drilling technology, not theory, is the constraint.

blocked by

instrumentation

This is a sourced, human-curated entry or a declared project limitation. It is not a computed discovery or an actionable hypothesis.