Deep in western Russia, there is a small collection of ragged scrap metal and crumbled concrete. After ruffling through this not-so-exciting rubble, one can find a large metal disc bolted to the ground. This isn’t just an ordinary old disc but the welded-shut cap of a borehole that plunges more than 12 kilometers (7.5 miles) into the Earth. That is deeper than the Mariana Trench, the deepest point of the ocean. In fact, this is the deepest hole ever dug into our planet.
This is the Kola Superdeep Borehole that exists purely for appreciating wonderful science of it all. During the 1970s, Soviet scientists started drilling down into Earth’s surface to find out more about the contents of the planet’s crust. Over the next 24 years, these scientists kept drilling on and off reaching over 12 kilometers by 1994. This abandoned achievement of humanity happens to be a record-breaking dig that still stands today and the drilling technology developed to get down there is pretty remarkable.
Hank Green explains in this 2014 episode of SciShow, “Because the truth is, we know less about what’s under our feet than what’s on the other side of the Solar System”.
The deep borewell showed us that there’s water at 12 kilometers into Earth’s crust, which scientists wouldn’t have even assumed possible had they not seen it with their own eyes. And nearly 7 kilometers down (4.4 miles), they spotted microscopic fossils of 24 species of long-dead single-celled organisms.
They also gained access to 2.7 billion years old rocks with temperatures around 180 degrees Celsius (356 degrees Fahrenheit), approximately 80 times hotter than what the scientists had predicted.