Editing Hollow Earth (section)

=== Direct observation ===
Drilling holes does not provide direct evidence against the hypothesis. The deepest hole drilled to date is the [[Kola Superdeep Borehole]],<ref>{{Cite web|url=http://www.iflscience.com/environment/deepest-hole-world/|title=What's At The Bottom Of The Deepest Hole On Earth?|date=11 March 2016 |access-date=2016-08-17}}</ref> with a true vertical drill-depth of around {{convert|12|km|mi|abbr=on}}. However, the distance to the center of the Earth is nearly {{convert|6400|km|mi|abbr=on}}.<ref name="...">{{Cite arXiv |eprint=1510.07674 |last1=Mamajek |first1=E. E. |last2=Prsa |first2=A. |last3=Torres |first3=G. |last4=Harmanec |first4=P. |last5=Asplund |first5=M. |last6=Bennett |first6=P. D. |last7=Capitaine |first7=N. |last8=Christensen-Dalsgaard |first8=J. |last9=Depagne |first9=E. |last10=Folkner |first10=W. M. |last11=Haberreiter |first11=M. |last12=Hekker |first12=S. |last13=Hilton |first13=J. L. |last14=Kostov |first14=V. |last15=Kurtz |first15=D. W. |last16=Laskar |first16=J. |last17=Mason |first17=B. D. |last18=Milone |first18=E. F. |last19=Montgomery |first19=M. M. |last20=Richards |first20=M. T. |last21=Schou |first21=J. |last22=Stewart |first22=S. G. |title=IAU 2015 Resolution B3 on Recommended Nominal Conversion Constants for Selected Solar and Planetary Properties |date=2015 |class=astro-ph.SR }}</ref>