Pulling a continuous cylinder of rock from kilometres below your feet is the closest thing geology has to time travel. Diamond core drilling is how the mining industry reads the subsurface before a single blast is fired. The bit does the work. A hollow annular crown studded with synthetic diamond grit grinds a circular kerf, leaving an intact rock column threading up through its centre into the core barrel. Diamond wins here because its hardness outlasts the quartz and feldspar that would shred tungsten carbide in metres. Then the elegant part: wireline retrieval. - The inner tube uncouples and is winched up through the hollow drill rods - The bit and the rod string stay downhole the entire time - A fresh inner tube drops back to resume cutting This avoids tripping hundreds of metres of rod out of the hole every run, the difference between crawling and real daily progress. Recovered core gets logged obsessively. Geologists measure Rock Quality Designation, the summed length of int...